Vyacheslav Yurievich! Thanks in advance for your topic "Homemade antenna designs for receivers with VHF (FM) band". I have little experience in this matter, but I really need an FM antenna (88-108MG) for the SONY ST-A35L tuner (I use 1 meter of wire for the antenna place). I tried to repeat your antenna from two aluminum tubes (I used tubes from ski poles with a diameter of 16mm). The length of each tube was 81 cm (photo 4), the gap between the tubes was 4 cm (I did everything according to photo 6) I used a 75 Ohm TV cable, I screwed the center of the cable to one alum, a tube, and the braid to another tube as in photo 6. I connected the other end of the cable to the tuner to the FM 75Om connector, center for the screw, braid for the clamp. Practically nothing has changed on the reception of stations, maybe I did something wrong. I live in a 5-storey building from the front is closed by a 9-storey building.

Good day! I cleaned the ski-pole tubes at the cable connection points with sandpaper. The receiver is located on the 3rd floor (house of 5 floors) in a room 3 by 4 meters near the window, from the window from the front of 200 meters there is a 9 floor building. There is no way to move the antenna to the roof. The receiver has 5 LEDs that show the received signal (on almost all radio stations that my receiver receives, only one LED is on, sometimes two LEDs in the evening). You are probably right, I need to assemble an antenna with a high gain. Can you tell me a little bit on the antenna.

Hello. Have you tried to place the antenna vertically (braid at the bottom), and then horizontally when receiving a radio station? How was the different position of the antenna reflected on the level indicator (on the bulbs)? In the case of horizontal polarization of the transmitter, the antenna should be turned (without touching it with your hands) in the horizontal plane to find the maximum reception level in order to ensure its optimal orientation to the transmitter.
The best results are obtained with the antenna in Photo 12, although theoretically such an antenna also has no gain. Perhaps, the material (metal-plastic) from which it is made plays an important role.
Homemade antenna made of metal-plastic for the FM range.
Antennas are more complex, that is, antennas with gain, at these frequencies are large, but purely for acquaintance, I present a drawing of the "wave channel" antenna. He's in this post
Homemade decimeter antenna "wave channel" made of metal-plastic.
The dimensions of the vibrator and reflector and the distance between them in the previous post. Everything else can be easily calculated from the drawing.

I have a music center Technics. frequency range stretched from 66 to 108, second floor, northwest, shadow zone. The room confidently receives at frequencies 101-108, stations of interest to me in the ranges 71-94, continuous hiss. I noticed that if I turn on the laptop, and even more so an additional monitor to it, then the interference is amplified. What I did was take an ordinary telescopic room TV antenna and brought it to the balcony, the reception improved, but there was no stereo, then I just took the pole and took the antenna out of the balcony by one and a half meters, twisted it - the reception became simply gorgeous! Apparently you have the same problem - interference from household appliances, equipment and wiring, perhaps a neighbor has a computer with a monitor on the opposite side of your tuner behind the wall. Try to take the anitena outside the wall of the house, just open the window, attach the antenna and expose the structure outside the window, twist .. I'm sure the reception will improve. And then, a matter of technology, to consolidate all this.

Hello. I tried to turn the antenna horizontally and vertically, carried it around the room, there was no strong effect. One thing I noticed is that the gain did not increase, but there was less interference in the reception, and the gain decreased at some stations. I will also try the HabarUral advice - take it out the window. There is also an idea to put an amplifier from a Polish antenna on the antenna.

Thanks for the article on FM Antennas for Tuners. I made a split antenna from 16 mm aluminum tubes, but did not get the effect. I would be grateful if you would give advice on what is wrong or "how to do it right."
An apartment in the center of Samara, a house at a high point, floor 11, walls - silicate brick, but all loggias are faced with corrugated board (this is almost the entire perimeter of the apartment, with windows). In my opinion, the signal should be very good. Tuner YMAHA, sensitivity specifications are below:
SECTION FM
Setting range
[USA and Canada models] ................... 87.5 - 107.9 MHz
[Other models] .................................... 87.50 - 108.00 MHz
50dB Sensitivity Calm (IHF, 100% mod.)
Mono / Stereo ... 2.0 mV (17.3 dBf) / 25 mV (39.2 dBf)
Selectivity (400 kHz) ............................................ 70 dB
Signal to Noise Ratio (IHF)
Mono / Stereo ............................................... .... 76 dB / 70 dB
Harmonic distortion (1 kHz)
Mono / Stereo ............................................... ...... 0.2% / 0.3%
Stereo Separation (1 kHz) .................... 42 dB
Frequency Response ........ 20 Hz - 15 kHz +0.5, –2 dB
On the original wire antenna (about 1.4 meters), reception with interference, with a vertical fastening of the wire, reception is better, my "walking" nearby affects the quality of reception and interference.
I made an antenna according to your recommendations, everything works, but not much better than a regular antenna-wire.
Also interference, antenna orientation is vertical. The upper tube is connected to the central copper core, the lower one with a 75 Ohm cable braid, the cable itself was passed through the lower tube for convenience (inside the tube) - perhaps this is a mistake. Perhaps there is a lot of interference in the house and the reason is this, only Wi-Fi networks(transmitters) at a given point of the apartment, about 10 pieces are "visible". (a couple of mine and from neighbors).
I wanted to attach a photo of the antenna and its location, but I could not do it in this blog window.
I will be a slave if you give me an email address, I can send a photo.

Yours faithfully,
Alexei
[email protected]

Vyacheslav Yurievich, good afternoon.
Thank you for your answer. There is no error with the sensitivity of the tuner, I checked it according to the original instructions (of course, there may be an error too. I will think about moving the antenna to the outer wall of the house, although this is not easy, if you have to do it well you have to hang out on ropes from the window, and this is the 11th floor.
I ask you to answer a few questions.

1) I stretched a 75Ω cable inside the antenna tube connected to the outer braid - in theory, can this affect the quality of the antenna's performance or not?

3) I saw on sale a 75 Ohm coaxial cable with two shields (central core, insulation, first shield, insulation, second shield, external insulation) Can you reduce interference using such a cable?

Yours faithfully,
Alexei
[email protected]

Vyacheslav Yurievich, good afternoon.

Thanks for answers. I will make an external antenna on the facade. Aluminum tubes of 81 cm are placed inside a polypropylene (not reinforced) water supply, between them a 4 cm textolite cylinder. The outer pipe will protect the antenna from precipitation and other things.

1) Is there a difference which tubes to use aluminum or copper (those and those 14 mm with a wall of 1 mm)?
2) When using a cable with two shields - connect both shields to the antenna beam (aluminum tube)? or alternatively only an external screen (or an internal screen)?

Yours faithfully,
Alexei
[email protected]

Vyacheslav Yurievich, good afternoon.
The question is purely theoretical.
Initial data: I live in the regional center, on the 8th floor in the shadow zone of FM radio transmitters. The radio transmitters are on the hill and in front of it, the house is behind the hill. The height of the hill is 150 meters. The house is from the highest point of the hill on a 70-80 meters drop. Reinforced concrete houses are in the direction of the transmitters. There is no direct line of sight to the transmitting antennas either from these houses or from my apartment. FM stations in the city - 15. On the external antenna of the receiver (wires 145 mm) 12 and 3 are caught in stereo mode. I put the antenna (copper wire 180 cm with a diameter of 4 mm in insulation) and screwed the central core of the RK-75 wire to one end of the wire without soldering. The 75 ohm cable sheath wire was left idle - not screwed on. external antenna input of the receiver - 75 ohms. I took the resulting vibrator to the balcony - 100 cm from the wall of the building. All 15 stations work in stereo mode.

The inconvenience is that a lot of space is occupied by a vibrator on the balcony (placed both vertically and horizontally).

The question itself is whether it is possible to reduce the antenna by leaving 75 cm of copper wire (a quarter of the wave in the middle of the FM band), located vertically, and twisting its remainder - 105 cm at 90 degrees in the form of a spiral with a diameter of 8-10 cm (you get 4-5 turns for antenna base)? Should the braiding of the coaxial cable be used (it can screw it to the copper wire 24 mm from the attachment point of the central conductor of the feeder (as in an antenna with a foil)? Will such an upgrade be effective?

Theoretical question - there is a gap of about 100 meters between the buildings in an open field, in the opposite direction from the transmitting antennas of our city, after 80 km another regional center. If I use a directional TV antenna of the UHF range with an amplifier (11 reflectors and a director), powered from 220 volts towards the gap between houses to another regional center, will I be able to hear the radio stations of another city in the same quality as from the transmitters of my city? The TV antenna of the UHF range in the village requires dismantling, therefore the question is theoretical. Thanks for the help.
Andrew.

Vyacheslav Yurievich, good afternoon.
Thanks for the complete answer. I also have success. I'll tell you about them and ask you to evaluate what has been done in terms of improving the antenna design from the available materials, which I will discuss below.
So, from a copper wire 4 mm in a vinyl braid, 180 cm long, I made a vibrator (75 cm) and twisted the remainder (105 cm) into a spiral as a base (stand) for the vibrator. The result is a stand of 3 full-fledged circles (an average of 35 cm along the circumference). To the receiver, to the input of the external antenna, I connected the cable RK-75 (2 mm in diameter - the size of a match for taking out through the balcony door without drilling additional holes). Socket in type F PRM. Antenna cable 20 meters long (from a radio store in the 1980s). He handed him around the room and led him out onto the balcony. The remainder was twisted in the form of a circle of the same diameter as the turns of the copper rod and put it on the vibrator, pressing down the spiral base of the antenna. I connected the feeder and the vibrator as follows: the central core at the bend of the copper wire by 75 cm (it turned out 1/4 of the wavelength of the middle of the FM range), the feeder braid was connected to the end of the copper wire on the opposite side of the vibrator, at the end of the base spiral. Soldered nothing, on a simple twist. I put the received antenna on the balcony, on the windowsill at the very corner. The balcony is glazed with metal-plastic windows. The distance from the concrete wall of the house to the antenna is 110 cm. Since the antenna is installed in the corner of the balcony, the aluminum edges of the balcony windows serve as a screen. The distance between the vibrator and the windows is 8-10 cm.
Result. I catch all FM stations in my city in stereo mode of 15 stations. Plus two stations of the regional center located at a distance of 40 km. They broadcast on their FM frequencies in stereo, but I catch them in mono and one unknown station in good mono quality from the neighboring area. There are 18 stations in total. Additional stations - as a result of the reflection of waves from neighboring houses located 10-12 meters higher than mine. The district center is located on the opposite side of a reinforced concrete building. That is, I am completely satisfied with the result, but still itching to improve something with the reception of waves without taking the antenna out of the balcony.
What can be done:
1. Shield the spiral under the vibrator at a distance of 75 cm and change the connection of the feeder sheath to the created shield.
2. Reduce the length of the feeder without the formation of wire turns on the base of the vibrator to 7 meters (I do not plan to increase the thickness of the wire RK-75 - it is too thick, the reception did not improve from this, I tried it).
3. Make a full-fledged dipole of 1/4 wavelength from a PVC water pipe by winding a copper wire with a diameter of 2 mm onto a 20 mm PVC pipe, 75 cm each on both sides.
4. Make a Pistolsky vibrator from a metal-plastic pipe with U matching.

Is it possible to improve an existing antenna with little effort?
Andrew.

Hello Andrey.
At the end of this post I have placed figure # 3 "Double Helix Antenna". If something like that happened, then it won't be better. All antennas considered in this post, be it a split dipole or a Pistolkors loop, are single-element antennas and have practically no gain. So, the Pistolkors loop has a gain of 0 dB, and the gain of all other antennas is counted from this (it is considered ideal) antenna. Only then will the antenna have gain when it has a unidirectional pattern, for example, due to the reflector or directors.
Finally, I didn't get it. In order not to take the antenna out to the balcony, we tried to connect directly to the antenna socket of the receiver: a quarter-wave piece of wire (75 cm), tubes, spirals, a wave ring (2.7 m)? After all, you can receive a reflected signal from houses.
For a quarter wavelength section or loop, I used a coaxial cable, the conductive layer of which is the outer braid.

Thanks for the consultation. Yes, apparently, a double helical antenna turned out, it may not be quite accurate in size, but the reception quality is quite satisfactory for city stations. And for long-distance reception there is the Internet and the AUX input of the receiver. Andrew.

I am reporting. The antenna option according to Figure 4 works worse than the dipole option according to paragraph 5 of my post from 7.2.18 11:16. How does it manifest? Lost stations in the wrong region. City stations are all in stereo. Does copper braided foil perform poorly? I wound the foil on the cable, fixed the cable sheath between the foil turns and tightened it with tape. With tape I wrapped all the foil along its entire length on the cable. On the vibrator, the braid was connected to the central core. The dimensions of the vibrator (700 mm), the gap with the counterweight (40 mm) and the counterweight itself (750 mm) were kept as in Figure 4. I placed them in a plastic pipe - I did not notice any improvements.
Wanted to try a half-wave vibrator powered at one end, but read on the internet that it works no better than a quarter-wave dipole and needs a transformer tweak. Although it has a good directional diagram (pinned to the ground) and reviews of radio amateurs-practitioners.
Cable is left for one more experiment. Which one are we going to conduct? I am leaning towards option 2 of my previous plan of experiments, namely: "2. Bend a piece of PK-75 wire 3 meters long in half and place it inside a plastic pipe. Connect the braid and the central core of the PK-75 cable placed in the pipe. The other end of this loop length L / 2, connect to the feeder: one to the central core, and the other to the braid without a matching U-elbow. L-300 cm is the wavelength of the middle of the FM range. " Do you approve, in terms of theory and your practice?
With all respect, Andrew.

OK. Let's fix the technology, try to connect the cable sheath to the foil wound on a 75 cm pipe and covered with tape. At the same time, we move the vibrator outside the pipe and attach it to any dielectric inserted into the pipe. For example, to a stick 40-60 cm long and tape the vibrator to the dielectric. The height of the structure will be: 200 cm pipe + 70 cm vibrator.

If, in any way, our pipe has an aluminum interlayer in a foamed polyurethane medium (PP-R / AL / PP-R is my pipe marking), then how does your proposed option differ from a split quarter-wave dipole on a metal-plastic white pipe or not a split dipole, which works decently for me on a regular RK-75-4 at a minimum cost?

It is possible to exclude aluminum in the pipe only due to the plastic cable channel under the wires, choosing the side of the 20 mm square, and place the cable channel in a heater (we make a thicker counterweight), on which to wind 75 cm of food foil and connect it to the cable braid. The diameter of such a structure will turn out to be 35-40 mm and under the foil - 25-30 mm. Then it will be a pure experiment, only there is no aesthetics in it.
With all respect, Andrew.

I made an antenna according to Fig. 4 of the text of the article according to your technology. I wound a 75 cm foil onto the pipe.To it I fastened the braid of the RK-75 cable with adhesive tape through a couple more turns of foil. I secured the junction with electrical tape and tape. Since the pipe is PVC with aluminum, it took the vibrator out of the pipe. I inserted a suitable stick into the pipe from the side of the screwed foil and tied the vibrator to it with electrical tape (70 cm + 4 cm gap). Together with a pipe and a vibrator, a construction of 2 meters was obtained (another piece of pipe). Technologically, such an antenna turned out to be more complicated than a continuous dipole made of a coaxial cable, where the braid was removed from the vibrator - the central core of the RK-75 cable and tied to the external insulation of the feeder with an electrical contact of the braid without breaking. The resulting second part of the dipole is attached to the cable with adhesive tape along its entire length 75 cm from the place where the braid is removed from the cable. A 75 cm central core is insulated and a 75 cm braid stripped from the cable and twisted into a copper wire about 2 mm thick. I mechanically connected this wire to the braid. This is instead of a "stocking", from a braid, turned back (I could not do that). I chose this antenna as a basis for comparison based on the sounding method of stations outside my region and high-frequency interference between stations (analog tuner).

Result: Antenna-base comparison catches 12 stations in stereo and 3 stations in mono not in its region in decent quality. The design of the dipole with the winding of the foil to the tube - 12 stations in stereo mode and 1 station in decent quality in a non-local region in mono mode. The high-frequency whistle is higher when going from station to station on this antenna. Since there are two antennas standing side by side on the balcony and I only switch to an external antenna on the receiver, one or the other antenna, you can compare without losing the sensation of reception from the previous antenna. The wires are the same RK-75-4. The length of the feeder at the reference base antenna is 2 meters shorter. The total length of the wires is 5 and 7 meters.
The pipe is 200 cm, because with a vibrator it turns out 270 cm, so as not to perforate it, it is with aluminum. But I found a piece of the same pipe, but of a shorter length and with a vibrator, I got a structure equal to the first antenna - 2 meters each. The feeder passes through the pipe in both cases. In principle, the miracle did not happen. Both antennas are about the same (all on twists without soldering, due to this the second antenna gives more interference and the cable is even longer. The cables are connected to the receiver with standard different "F" connectors).

I will try another version of the antenna and finish with the experiments. Thanks for the help and advice.
With all respect, Andrew.

Nevertheless, the antenna according to Figure 4 of the article works better. If you create equal conditions, remove the PVC pipe from the comparison base antenna, then it does not catch 3 stations of the neighboring region, but only its 12 stations in stereo mode with the same interference (HF whistle between stations). I wrote about the pipe above - it serves as a screen for removing HF interference in an unbreakable dipole, and in the antenna according to Fig. 4 articles there is no such screen for a vibrator. In equal conditions of the experiment, everything changed from accuracy to the opposite.

The new antenna is based on the Pistolkors vibrator. PVC pipe (green, not metal-plastic) with a diameter of 20 mm, length 2000 mm. The wire from under the 380 volt cable is stranded - 16 copper wires, braided into one insulating sheath, 1.5 mm each. Heavy in weight. I cut off 3 meters. From the ends I make a ring for attaching a coaxial cable with a diameter of 3 mm. I split the wire in half (bend it). I slightly shift one side relative to the other so that there is a distance of 40 mm between the rings with the loop fully extended. Starting from the end, I tie a PVC wire to the pipe on two opposite sides of the pipe, at 180 degrees. I stretch and fix it every 10-15 cm with electrical tape or tape. And so on until the end of the wires (up to the rings). The result is a loop with dimensions: the thickness of the wire is 6 mm in rubberized insulation, the distance between the wires is 20 mm, taking into account the insulation - 23-24 mm. I am making a meter matching device from a piece of RK-75 coaxial cable. I fold a piece of cable 110 mm in half and tighten it with electrical tape (10 mm for twisting the central core). It turned out 500 mm. I connect one central core of the matching device to one end of the loop (with a simple twist), and connect the other end of the loop to the second central core of the matching device. I connect the central core of the RK-75-4 coaxial cable with a braid in the form of a copper mesh to one loop of the loop (any). I connect the three ends of the braid (two from the matching device and one from the coaxial cable) with a twist and wrap it with food foil 40 mm wide in several turns and fix it with electrical tape. The distance between the loop rings is 40 mm (one above the other along the pipe from opposite sides). I connect the cable to the matching device in three places with electrical tape. I attach the entire structure of the matching device with the cable to the PVC pipe with electrical tape or tape. It turned out exactly 2000 mm of this whole structure (1500 mm antenna and 500 mm matching device). I connect with a stereo FM receiver to an external antenna through the "F" type connector. I take out the antenna to the balcony and put it vertically in the corner of the balcony, where I put all the previous antennas. There, an artificial reflector is obtained from the junction of two metal-plastic frames and an aluminum connector. I turn on the receiver.

3-4 stations are caught in stereo, the rest in mono. The result did not satisfy me. I turned the antenna horizontally, put it on the balcony windowsill and pointed it to the sky. I started to turn the receiver's vernier and a miracle happened. Stations in stereo sound like sitting in a concert hall. Deep stereo effect, no interference and clear sound. I achieved this for 2 weeks of experiments with different antennas.
Compared with the antenna in Fig. 4 of the article. The sound in stereo mode differs significantly from the new antenna - the sound is quieter and there is no such depth of the stereo effect, although the stereo signal in the form of a lamp does not blink, i.e. tuning to the wave is good.

Features. The antenna turned out to be narrowly directional with good noise reduction, and due to the aluminum core in the form of a PVC pipe, also with amplification, apparently. A 45 degree angle also works, but not all stations are in stereo.
Here is an experience of experimental selection of antennas for urban listening to stereo FM. Receiver - Sangean WR-12. For 30 years, the cable has been waiting in the wings and finally benefited the owner.
Thanks for attention.
Laying technology. We ideally need to lay the wire in the form of a rectangle, where the height is 2 times the base. We make a gap of 2 cm on one of the vertical sides - in the middle. For a wire of 306 cm, we get a rectangle: 306/2/3 = 51 cm - this is the length of the base. 51 * 2 = 102 is the height of the frame. Why exactly this size of the frame - no need for matching devices. Where the coaxial cable is connected, there will be a resistance of 75 ohms. We attach the cable to the frame as follows: the braid is at one end of the gap on one side of the frame, and the central core at the other end. These are ideal installation conditions. But if the window is already 51 cm or wider by 1-2 cm, then you have to fit the frame along the width of the window (up to glazing beads on a wooden frame, and for plastic windows - up to glass holders - clips).

As I did, I measured the width and height of the plastic window against the glass. One was 51.5 cm wide and 130 cm high, and the adjacent, adjacent one was smaller in width by 3 cm. I had to make two frames on adjacent windows and, in addition, the windows are located at 90 degrees - this is the corner of the balcony. I measured 50 cm up from the bottom of the window on the glass and fixed one of the ends of the wire with ordinary tape, making a lapel 1 cm towards the window frame at 90 degrees. Then we lay the wire down to the end of the window, i.e. to the bottom. We fixed the corner with tape. We walked along the bottom to the opposite side of the frame - we got the bottom of the frame and half of one side of the frame with a gap for the cable. We laid the wire up to a height of 102 cm. We fixed the corner - the upper corner of the frame with tape. Then horizontally to the opposite side of the frame. Fastened the corner and down until it breaks. To create a gap of 2 cm in the break of the side (I have the right side of the first frame) - we bend the wire towards the plastic of the frame and fasten the gap with tape, leaving the bare ends of the wire for attaching the coaxial cable with a resistance of 75 ohms. To prevent the wire from sagging, we fasten it with tape every 10-15 cm both vertically and horizontally. We do not connect the cable.

We attach the second piece of wire 306 cm to the adjacent window, but using a different technology. We need to connect two frames to one cable, so with tape we attach the break of the second wire to the plastic frame (it will be 2 cm). We got a 7 cm wide frame of 2 cm wires parallel to each other, and in the center there is a place for connecting the cable to the receiver. Next, we stretch the wire along the perimeter of the window so that we get a frame with the same upper and lower sides. First, we fix the corners, and then the wire between the corners, 10-15 cm each.

We get two frames on adjacent windows, but one is strictly in a rectangle 51 X 102 cm, and the other is smaller, by stretching the gap until the side of the other frame joins with the gap (I got 7 cm across the width of the window frame). We connect the coaxial with two frames at the break. I connected the central core at the top, and the braid at the bottom of the gap. I twisted the wires - they are all copper. It is clear that soldering on the window is not worth and is not worth it.

The direction of the frames is one degrees at 30 degrees to the tower of the transmitting center, and the other is 120 degrees. At a distance of 110 cm behind the first frame, there is a concrete wall of the building serving as a reflector. At a distance of 320 cm, another concrete wall of the building is a reflector for the second frame. Since the two frames on the windows are at an angle of 90 degrees and with reflectors, the main lobe of the directional diagram of the two frames turned out to be at an angle from the transmitting center, 80-90 degrees from the transmitting center. Polarization - vertical two frames, because the gap is at the height, not at the base of the rectangular box.

As a result, all radio stations in your city are in stereo mode with good sound depth and stereo effect. We catch repeaters on other frequencies of regional centers and 2 programs from a neighboring region in stereo mode. The best antenna I have tested and described above.

Improving the stereo effect due to the capacitive component and the width of the frame wire. Replaced the usual wire 1 mm thick under the frame - with a double 1.5 mm each core of the wave rope type (noodles). I connected the ends of the parallel wires at the junction with the coaxial cable and laid the wires instead of the previously used ones. Two pieces of double cable, 306 cm each. I got the best stereo effect and a slightly wider directional diagram, judging by the loudness of poorly caught radio stations from the regional centers' repeaters (it has decreased). I decided not to change the wire back (noodles for single-core).
I am writing for those who want to have an antenna "with their own hands" in the form of frames on the balcony window.

With all respect, Andrew

FM antenna based on beer can antenna, but without them.
Beer cans are used to make TV antennas with horizontal polarization. For FM reception you need - vertical.
I decided to conduct an experiment with water bottles (1.5 liters of plastic). I poured about 1 liter of water into one (for the stability of the structure). He fastened the caps of two bottles together with a bolt and a washer in the center. I screwed the fastened caps onto an empty 1.5 liter bottle, and the second onto a bottle of water. We got one plastic bottle on top of the other. We take a foil for baking (I have a foil 29 cm wide and 11 microns thick). I screwed it onto the bottom bottle 3 turns (it turned out from the very bottom to 2 cm from the lid). I fixed the foil with tape in 3 places: in the center, from the edge at the bottom and 2 cm from the edge of the foil at the lid. He took off the top bottle and did the same with it. I screwed on the lid and connected the two bottles. We take a 75 ohm coaxial cable, make a U type matching device 1 meter long. We twist it with a coaxial cable: three braids together; twist the two central cores (one from the feeder and the other from the matching device) and leave a free end of 3 cm for attachment to the foil; we expose the central core of the second end of the matching device 3 cm. We connect everything like this: we push two twisted central cores between the foil loops on the lower bottle and tighten them with tape, pressing them to the bottle, we do the same with a piece of wire 7-10 cm long and attach one end to the second, upper bottle. We needed a piece of wire so that we could unscrew the bottles and replace the water with sand when it dries out from the snow. We connect the other end of the wiring with a twist to the free central core of the matching device. That's it - the antenna is ready. We carry out tests. The matching device was screwed with tape to the bottom jar, although it would be correct to place it at 90 degrees to the bottles. We are looking for a place on the balcony, on the windowsill. The directional diagram is circular at the antenna, moving the bottles at a distance of 39 cm from the reinforced concrete wall - we get a directional diagram away from the reinforced concrete wall (39 cm is 0.13 wavelengths in the 300 cm (mid-FM) range). We select the height of the bottles on the windowsill so that they are in the middle between the ceiling (reinforced concrete plate) and the floor - the same plate. We turn on the receiver - all city FM stations are in stereo over the entire width of the FM range from 88 to 108 MHz. The stereo sound in the receiver is not flat, voluminous, comparable to the stereo sound from a double square antenna (my post above from February 21). the distance between the foil of the two bottles is 10 cm between the attachment points of the feeder to the foil (7.5 is recommended). It is clear that it will not be possible to conduct an experiment by decreasing this distance. In general, for a portable receiver, one of the options for an external antenna.

3. For better contact of the braid and the central core of the cable to the foil (without a matching device, we attach the central wire and the braid to different bottles between the foil loops) - screwed the M6 ​​washers and then pushed them between the braid loops to a depth of 1 cm and pressed them with tape to the bottle in 2 turns.
4. Construction height - 66 cm, bottle circumference - 28 cm. Bottles without tapering under the arm in the middle of the bottle.
5. The foil can be wound onto a cardboard tube, leaving a gap between the foil turns of 7.5 - 10 cm (the larger the tube diameter, the greater the distance between the ends of the foil). Foil can be glued to cardboard, but the glue consumption is high. Since the foil clings to objects during transportation and breaks, it is better to wrap it with tape along its entire length.
With all respect, Andrew.

Good afternoon, V.Yu.
We are switching to magnetic antennas for receiving FM radio stations in dense buildings and balcony-window options. I made a loop antenna from one piece of copper wire with a diameter of 3 mm on a balcony glass with a perimeter of 306 cm with a gap in the larger side of the rectangle (43x110, gap 2 cm). Replaced the previously installed antenna of the same size, but from a flexible wire 2x1.5 mm. I was not impressed with the results. The antenna turned out to be narrowband (the setting was at 100 MHz). Significant signal attenuation was felt at frequencies above 107 MHz and below 97 MHz. Subtracted that a loop antenna with a frame perimeter of less than a quarter of the wavelength is more sensitive to the magnetic component of the wave, rather than the electrical one. The second premise is that there is resonance at frequencies that are multiples of the wavelength. A loop antenna is effective when the perimeter of the loop is equal to the wavelength. An idea came up - to make a frame at a frequency that is a multiple of the wavelength, but less than a quarter.
I started counting - 100 MHz - the average frequency of the FM range (with a wavelength of 300 cm), but what if we increase the frequency by 5 times? We get 500 MHz and a wavelength of 60 cm. Then the frame is obtained with sides of 10x20 cm. With such aspect ratios, no coordination is required. We will make a gap on one of the small sides of the rectangle of 2 cm (cut and bend the wire 1 cm to the sides). In fact, we begin to bend the wire (Ф = 3mm) from one end: 1-4-20-10-20-4-1 = 60 cm. Since I do not welcome soldering in experiments, I used the 1 cm vinyl braid as a clamping device. He pushed the central core of the coaxial into it and fixed (pulled) onto the end of the frame. Braid the coax to the other end of the frame. That's it - the antenna is ready. RK-75 cable with copper braid (so that there is one antenna and coaxial material). The length of the cable is 40 cm (there was just such a piece without use). Began testing.
A room in a w / w house. no result. Something catches, but dips in the signal level from different stations.
I went out with the antenna to the balcony - I put it next to the metal-plastic frame on the windowsill and in the corner of the balcony (there is a slab on top, a slab below, a wall of the balcony - reinforced concrete), from the wall at 0.17 wavelengths - 50 cm.
And here the bite began - I did not have time to shoot a fish and a large and very large one, in the sense of the FM station one after another with a high signal level. All stations in stereo in their city and a couple of stations in mono in a neighboring region (80 km).
He continued testing by moving the frame on the windowsill up and down, left and right. I found out that the closer to the metal-plastic window, the better the signal. The distance from the reinforced concrete wall was calculated correctly. Elsewhere, the signal was attenuated, but was not comparable to the signal level in the room. I left the frame in the place with the strongest signal strength and connected an 11 meter cable. I sit listening in a room on such a small antenna and enjoy the signal level and sound quality. The signal level in dB for all stations is 475 dB, and a metal-plastic phased antenna with a circumference of 73.5 cm showed the result on the same balcony, but in a different place (opposite) - 479 dB. But the sizes are not comparable on the balcony. Received gratitude for this from my wife.
This is how scraps of knowledge of radio engineering synthesized in practice an antenna suitable for use in my conditions. Practice is the criterion of truth !!! Reply Delete

Over and over again, VHFs ask their senior colleagues, "Which antenna to choose?" It is impossible to accurately answer this question, since everything depends on the purpose for which the antenna is being built. If communications are assumed in all directions, for example, within a city, then antennas with a circular pattern are very convenient, which often allow operation at distances between stations equal to 50-100 km. Directional antennas are more suitable for long-distance communications. In "densely populated" VHF areas or in cases where interference comes from some directions, it is undoubtedly better to use highly directional antennas.

These few examples are enough to understand that there is no antenna that is equally suitable for all situations. The radio amateur must choose an antenna that meets his basic requirements. Better yet, build two or three antennas and use them as needed.

It is unwise for a beginner VHF to choose as his first antenna any bulky and complex structure, in the process of building which he, due to inexperience, can make many mistakes. You should start with the construction of the simplest antennas and, as experience and knowledge grow, move on to more complex systems.

When choosing the type of antenna, it is necessary to take into account what basic materials are available to the designer. If pipes or rods for antenna elements cannot be purchased, then you can choose, for example, a "double square", the construction of which requires only wire, wooden slats and a small amount of insulating material. It is also essential how the supply line will be made - from a coaxial or ribbon cable, or simply in the form of a two-wire line.

It should not be overlooked whether any measurements are needed in the construction of the antenna. For a beginner, who also does not have measuring equipment, it is better to choose an antenna that will probably work well without tuning.

Consider a number of antenna types. These include simple designs that every beginner can repeat, and sophisticated ones, including antenna systems, that may be of interest to more experienced DX hunters. Since most of our VHFs operate in the 144 MHz band, antenna sizes are shown for this band.

The reader will note that no technical design details are provided for any of the antennas. But this should not interfere with the construction, since the methods of work and many details are described in any handbook of the radio amateur.

CIRCULAR ANTENNAS

Cross dipole. The antenna consists of two half-wave vibrators 1 located at an angle of 90 ° to each other (Fig. 1). The radiation pattern of this antenna is far from a perfect circle, but in practice it gives quite good circular radiation. Since the characteristic impedance of one dipole is about 70 ohms, when two dipoles are connected in parallel, the characteristic impedance is about 35 ohms. We do not have such a coaxial cable, so it is best to power the antenna through a quarter-wave transformer 3, made of a 50-ohm cable. A 75-ohm cable 4 runs from the transformer to the equipment. A balancing U-elbow 2 is made of the same cable.

Vertical antenna (Ground Plane). Emitter 1 (Figure 2) and radial conductors 2 provide a circular pattern in a horizontal, plane. The angle between the radial conductors and the radiator determines the characteristic impedance of the antenna.

fig. 2

At an angle of 90 °, the characteristic impedance is approximately 30 ohms, at an angle of 180 ° - 70 ohms. Typically, an angle of 145 ° is selected, which allows the antenna to be fed with a 50 ohm cable. The cable is connected to connector 3, fixed on a metal plate, to which radial conductors are electrically connected. The emitter, to which the central conductor of the cable is connected, is installed on the insulator 4.

DIRECTIONAL ANTENNAS

"Double square". This most popular directional KB antenna is also used on VHF (Fig. 3, a). Its gain (in comparison with a half-wave vibrator) reaches 5.7 dB, the forward / backward radiation ratio is 25 dB.

fig. 3

The distance between the active vibrator 1 and the reflector 2 is chosen equal to 0.15 lambda, which allows the antenna to be fed with a 75-ohm coaxial cable 3. Experience has shown that the antenna fed in this way works quite satisfactorily. You can tune the antenna using a short-circuited loop included in the break of the reflector frame.

To balance the antenna, you can use a quarter-wave glass (Fig. 3, b) by connecting it to the ends of the active vibrator 1. The glass consists of a metal cylinder 4 with two covers - metal 5 and dielectric 6. Cable 3 passes inside the glass, the cable sheath is connected to the cover 5. The diameter of the glass should be 3-4 times the diameter of the cable.

For the manufacture of antenna elements, you can use a copper or aluminum tube, tape or wire of various diameters. "Double square" takes up very little space and is structurally simple. This antenna has comparatively good performance. Noteworthy is the possibility of placing antennas of different ranges on the same cross-shaped rails.

Delta Loop Antenna belongs to the same family as the "square", since the perimeter of the active vibrator is approximately equal to the wavelength. The peculiarity of this antenna is that all elements of its structure are metal. The author of the antenna advised to feed it with a 50-ohm coaxial cable, but a 75-ohm cable is also successfully used for this purpose. The simplest triangular antenna is shown in Fig. 4. The active vibrator 1 is tuned using a gamma-matching device to which the cable 3 is connected. Depending on the availability of measuring instruments, the tuning is carried out according to the minimum SWR or according to the maximum signal strength. Reflector 2 can be made unregulated for simplicity.

fig. four

UA1WW experimented a lot with a triangular antenna. He advises using 5- and 9-element variants. The latter, due to the small horizontal angle of radiation, is especially suitable for long-distance communications. A drawing of a 5-element antenna is shown in Fig. 5. Here 1 is an active vibrator, 2 is a reflector, 3-5 are directors. Since this is a completely new antenna for our VHFs, we present some design data.

fig. five

A 4-sided duralumin pipe with a side of a square of 18-20 mm is most suitable for a load-bearing traverse; it is much more convenient to attach elements to it than to a round pipe (see Fig. 6).

fig. 6

The antenna elements are made of a copper or aluminum tube or rod with a diameter of 6 mm, the horizontal side is made of a wire with a diameter of 3 mm. The dimensions of the elements (in accordance with Fig. 6) are as follows:

Triangular antenna- an object of interest for ultrashort wavelengths around the world. Taking into account the positive experience of working with it, we can assume that it will soon become one of the most popular antennas. Therefore, we draw the attention of those wishing to experiment on one special type of it - a double triangular antenna (Fig. 7). The dimensions of the triangles of this antenna are slightly larger than those of a single antenna; the perimeter of the reflector is 2266, the perimeter of the active vibrator is 2116 and the perimeter of the director is 1993 mm. The distance between the reflector and the vibrator is 0.2 lambda, between the vibrator and the director is 0.15 lambda.

fig. 7

According to some data, the following gains of a double antenna (in comparison with a half-wave vibrator) were obtained: one element (active vibrator) - 3-4 dB: two elements (vibrator and reflector) - 8-9 dB: three elements (reflector, vibrator in director), - 10-11 dB. This seems like a promising antenna view and worth tackling.

10-element antenna (Yagi). This is undoubtedly the most popular VHF antenna (Fig. 8). It gives a gain of 13 dB. The author made meteor contacts with England and Belgium with the help of such an antenna, many long-distance contacts due to tropospheric passage and "aurora".

fig. eight

The passive elements of the antenna are made of a bimetallic wire with a diameter of 4 mm, and the active loop vibrator is made of a 15 mm copper tube and the same wire. The impedance at the feed point is 300 ohms, so the 75 ohm cable is connected through a 68 cm U-elbow.

The length of the bearing crosshead is slightly more than 3.5 m, the diameter is 20 mm. The length of the reflector 7-1060, vibrator 2-990, directors 3-10 - respectively 933, 930, 927, 924, 921, 918, 915 and 912 mm.

Antenna for multiple bands. There are circumstances when it is not possible to install more than one antenna. But in addition to an antenna, a television station is often needed for a radio station! Then the way out is a UKB antenna for several bands. One of the variants of such an antenna is shown in Fig. 9, a (top view) and 9, b (axonometric projection). It can be successfully used in the 50 to 220 MHz bands. The antenna gain at a frequency of 50 MHz is 7 dB, 144 MHz is 12 dB, and at 220 MHz it is even 13.5 dB. This antenna is a two-story antenna. At a frequency of 50 MHz, two corner vibrators 1, located at a distance of lambda / 4, operate on each floor. At 144 MHz, their length is about 3/4 lambda, and therefore a V-shaped antenna is obtained. At 220 MHz, the vibrators are 5/4 lambda long.

fig. nine

The vibrators are interconnected by two-wire lines 2, and both floors are connected by lines 3, the length of which, depending on the range, is from 1/4 to 5/4 lambda. The distance between the floors, if desired, can be changed within the limits allowed by the length of lines 3. The input impedance of the antenna at feed point 4 at frequencies of 50 and 144 MHz is about 300 ohms, at a frequency of 220 MHz it drops to about 200 ohms.

Antenna elements can be made from a tube or a rod: vibrators - 10 mm in diameter; line 2 - with a diameter of 12 mm (10 mm is also possible, then the distance between the centers of the wires of the line should be chosen equal to 64 mm): line 3 - with a diameter of 6 mm.

RADIO No. 8, 1973 pp. 20-23.

Antenna designs are described, as well as schematic diagrams antenna amplifiers for a homemade VHF radio station (diagram and description) for the frequency ranges 144MHz, 430MHz and 1296MHz.

About the characteristics of VHF antennas

The efficiency of the antenna is unambiguously related to its geometric dimensions, for this reason, the antenna is the only device included in the radio station, which has not been touched by the process of miniaturization of radio equipment.

The manufacture and installation of an antenna is a rather complicated and time-consuming business, especially since the issues of strength and rigidity of mechanical structures have to be addressed. Nevertheless, increasing the efficiency of the antenna is the only unrestricted way to increase the energy potential of the radio station.

Any antenna can be represented as an equivalent area standing in the path of radio wave propagation. The larger its area, the greater the antenna gain, formula:

where G is the antenna gain in relation to the isotropic radiator; S - equivalent area, m2; lambda - wavelength, m

From an energy point of view, it does not matter what shape the equivalent site will have: whether it is round, square, or has the shape of an elongated rectangle. In any case, for an equal area, there will be an equal gain. The directional diagram is another matter; the shape of the equivalent site has the most direct effect on it. So, the width of the main lobe of the radiation pattern can be related to the linear dimensions of the area by the following approximate expression (formula):

A0 (delta_0) - the width of the main lobe at the level of -3 dB; hail; lambda - wavelength, m; l is the linear size of the equivalent area in the plane of measurement of the radiation pattern, m.

This formula, rewritten in a different form, makes it possible to estimate the size of the equivalent area from the known radiation pattern: l = 50 * lambda / delta_0.

Suppose, for example, tests of a 432 MHz antenna have shown that the beam width is 25 ° in the horizontal plane and 20 ° in the vertical plane. It is easy to determine that an equivalent site will be 1.4 m horizontally and 1.75 m vertically.

Such estimates are very convenient if it is supposed to increase the gain by connecting several antennas to an antenna array. So, for the example considered, the distance between adjacent floors of the array should be 1.75 m, and between adjacent rows - 1.4 m. At smaller distances, the equivalent areas will overlap and the total gain will be less than the sum of the gains of all antennas.

At large distances, gaps will appear between the individual sites. As a result, the overall gain will not increase, but the size of the antenna will unnecessarily increase. At the same time, dips appear in the main lobe of the radiation pattern, dividing it into several components.

And although the presence of such dips can sometimes be beneficial (for example, if it is necessary to tune away from interference, the azimuth of which differs little from the azimuth of the correspondent), in most cases such a directional diagram makes it difficult to work on the air.

Returning once again to the issue of antenna gain, it should be noted that in the general case, the gain is the product of the directional action and the gain useful action antennas (formula):

where K - Ph.D. antennas; n - efficiency antennas. This means that it is not enough to make an antenna of a large area, it is still necessary to be able to deliver all the energy falling on a given area with minimal losses to the consumer of this energy, that is, to the input of the receiver. (Hereinafter, we will use the "reciprocity principle" valid for antennas, which indicates the equivalence of the antenna parameters in the transmit and receive modes. For example, the radiation pattern or efficiency does not depend on whether the antenna is used for receiving or transmitting. This allows each time to choose the most convenient mode of operation of the antenna for reasoning.)

The emission of electromagnetic energy is associated with the flow of high-frequency current, therefore, the losses in the antenna itself are determined by the ohmic losses in the metal elements. Losses in cable lines have a great influence on the efficiency of the antenna-feeder path, which must be taken into account when assessing the energy potential of a radio station. It is useful to remember that the antenna-feeder path is used for both reception and transmission and, therefore, the losses in the feeder will be twice included in the final result.

The table shows brief information about some high-frequency cables that are used in amateur radio practice. It can be seen from the table that with increasing frequency, the losses in the feeder increase rapidly.

So, for example, a 20-meter section of cable of the RK-75-4-11 type (the old name of RK-1) attenuates the signal passing through it at a frequency of 144 MHz by 2.1 times (3.2 dB), at a frequency of 432 MHz - 3.4 times (5.4 dB), and at 1296 MHz - 13 times (11.2 dB). It can be seen that at high frequency ranges, losses increase to unacceptable values.

In addition, here the data is given for the case when there are no reflections at the ends of the line, that is, for the case of working at a matched load. If the load resistance differs from the wave impedance of the cable, then part of the energy is reflected from the end of the cable and moves in the opposite direction.

This reflected portion of the energy can only return to the load after it has traveled a double path from load to generator and back from generator to load. If the losses in the feeder are small, then such multiple reflections are quite acceptable.

This “tuned feeder” mode is particularly used in some types of multi-band HF antennas. On VHF, where the losses in the feeder increase sharply, it can be assumed that the part of the energy reflected from the load is almost completely lost. The situation, however, is not as bad as it might seem at first glance. In order to estimate the mismatch loss, let us write the c.s.w. as a function of the reflection coefficient (formula):

here Г is the reflection coefficient;

from here it is easy to obtain an expression for calculating the amount of losses (formula):

Fig. 31. Technical and wave parameters of coaxial cables.

This expression is graphically shown in Fig. 32. It can be seen that even with f.s.c. = 3, the losses reach only 25%. If the losses in the feeder itself are not very high, then due to the partial return of the reflected energy, the reflection losses will be even less.

So, for the case of 2 dB loss in the feeder, the reflection loss at f.s.s. = 3 decreases from 25 to 20%. It can be seen that there is no point in striving for c.s.v. = 1.1 or even 1.01, the cap is given in the description of some amateur radio antennas. So, at f.s.i. = 1.5, the loss of pa reflection, even in the worst case, will be only 4%. Hence, it follows that without any special losses it is possible to feed an antenna with an input impedance of 50 Ohm using a coaxial cable with a characteristic impedance of 75 Ohm, since in this case the c.s. will be equal to 1.5.

Fig. 32. Dependence of the return loss on efficiency. in.

Let us now consider the features inherent in the antenna-feeder system in the receive mode. In this mode, the noise properties of the antenna begin to play a significant role. For this reason, the concept of noise temperature is often introduced for the receiving antenna. If, for example, the noise temperature of the antenna is 200 K. then this means that the antenna generates the same noise that it generated

would be an active resistance heated to a temperature of 200K. Antenna noise is a combination of external and internal noise. External noise is the source of interference that fundamentally limits the ability to receive weak signals.

When the antenna is directed towards the horizon, this is primarily the thermal noise of the earth's surface, various kinds of industrial interference, as well as noise of cosmic origin. Internal noise is determined by the presence of losses in the antenna and the feeder. Like any resistance, loss resistance generates "thermal noise."

For this reason, the sensitivity of the receiver deteriorates not only due to the attenuation of the received useful signal in the feeder, but also due to the fact that the feeder generates additional noise. Both of these factors are taken into account in a simple formula „for an attenuator heated to ambient temperature. The receiver noise figure, taking into account the loss in the feeder, is (formula):

where Ftot is the resulting noise figure; L - attenuation in the feeder or in any other passive four-port network; Fпр is the receiver's own noise figure.

Thus, knowing the receiver noise figure and calculating the feeder attenuation using the table, it is easy to determine the resulting receiver noise figure at the antenna terminals. You can also solve the inverse problem, that is, by measuring the noise figure with and without a feeder, determine the loss in the cable. This is a more reliable way, since for various reasons, real cable losses can differ significantly from tabular ones.

It can be seen that the losses in the feeder have a significant impact on the potential capabilities of the radio station. As a result, the effort involved in making a large and complex antenna can be negated. And if in the transmission mode it is still possible to somehow compensate for the losses in the feeder by increasing the power, then in the reception mode the losses are irreversible. Antenna preamplifiers located in the immediate vicinity of the antenna help to solve this problem.

The question of the need to use such an amplifier must be decided in each specific case by comparing the external noise of the antenna and the internal noise of the receiver. In order to ensure normal operation input circuit receiver, instead of the antenna, a resistor must be connected, the resistance of which is equal to the characteristic impedance of the feeder.

If, even in the most favorable night hours, the antenna noise noticeably (2 times or more) exceeds the resistor noise, the antenna amplifier should not be used. Moreover, an extra amplification stage will make the receiver more vulnerable to interference from nearby radio stations.

In order to connect a preamplifier in receive mode, you need to have two high-frequency relays or one relay and a separate feeder connecting the preamplifier output to the receiver input.

VHF antenna preamplifier circuits

The antenna preamplifier circuits can be borrowed from the traisverter circuits of the corresponding ranges. For example, in Fig. 33, a shows a diagram of an antenna amplifier for the 144 MHz range, and Fig. 33.6 - for the 432 MHz range.

The tuning method of the preamplifiers does not differ from the tuning method of the corresponding transverter stages.

If the antenna relays do not provide sufficient isolation, the problem arises of protecting the preamplifier from the transmitter signal. As one of the protection measures, diodes D1 are included in the base circuit of the transistors. When tuning, be sure to check whether the connection of the protective diode will impair the noise figure of the preamplifier.

Fig. 33. Antenna amplifier circuits.

Protection problems completely disappear if a powerful multi-emitter transistor KT610 or KT911 is used as a preamplifier. A schematic of such a 144 MHz preamplifier is shown in Fig. 34. Coil L1 contains two turns of 1.0 mm silver plated wire.

The diameter of the mandrel is 10 mm. Setting up the amplifier should begin with setting the DC transistor mode. By selecting the resistor R1, it is necessary to achieve that the collector current of the transistor is 15-25 mA.

Fig. 31. Antenna amplifier of 144 MHz range, made on a multi-emitter transistor.

The preamplifier has the following characteristics: a gain of about 20 dB, a noise figure of 1.5-1.8. To prevent the failure of subsequent amplification stages, it is advisable to remove the supply voltage from the T1 transistor in the transmission mode, and even better to connect the preamplifier power wire to ground.

VHF antenna designs

Let's now look at some practical antenna designs. For many years, the most popular among radio amateurs have been the wave-channel antennas, which are also known as; "Yagi antennas" and "Uda-Yaga antennas". These antennas, classified as axial-emission antennas, have the best gain-to-mass ratio and are also very simple in design.

The main disadvantage that has limited the use of such antennas in industrial communications is their narrow bandwidth. However, for radio amateurs, this disadvantage does not play a big role, since the width of the ranges allocated for radio amateur communications is also small.

Recently, numerous attempts have been made to improve the wave channel antenna in order to increase its gain. A section of a log-periodic antenna (antenna of the "Swan" type) was used as an active element, or more complex passive elements were used, consisting, for example, of four half-wave vibrators (numerous types of antennas produced by Western countries for receiving television at decimeter waves).

However, all these tricks do not give a significant gain, since ultimately the gain of any antenna with axial radiation is determined by its length. The use of more sophisticated vibrators is equivalent to the use of several conventional “wave channel” antennas located at a very small distance from each other. As already mentioned, this is equivalent to an almost complete mutual overlap of equivalent sites, and therefore, the resulting gain is also small.

Fig. 35. Eight-element Quagi antenna for 144 MHz, dimensions for 432 MHz are given in parentheses.

Of the advanced wave channel antennas, the Quagi type antennas are perhaps the most interesting. The name is made up of two English words "Quad" and "Yagi" and indicates that the antenna is a hybrid of a "square" type antenna and a "Yagi" type.

Actually, only the active element and the reflex frame are taken from the "square", and all the directors are the same as in the "wave channel" antenna. The antenna is powered by a 50 Ohm cable. The cable is connected directly to the break in the active frame without any matching device.

The reflector frame has a perimeter of 2200 mm (711 mm), and the active frame has a perimeter of 2083 mm (676 mm). Hereinafter, the dimensions for the 432 MHz band are indicated in brackets.

Both frames are made of copper wire with a diameter of 2.5-3 mm and are fixed to the supporting crossbar using organic glass strips. The bearing traverse has a length of 420 cm (140 cm) and is made of a wooden, better pine, bar with a section of 2.5X8 cm (1.2x5 cm). To facilitate construction, the height of the bar can be reduced towards the ends of the antenna. The directors are made of aluminum or copper wire with a diameter of 3 mm.

The output impedance of the antenna is 50 Ohm, however, without large losses it can be powered by a cable with a characteristic impedance of 75 Ohm. When using multiple antennas, the distance between adjacent floors and rows should be 3.35 m (1.09 m).

The more efficient Quagi antenna designed for the 432 MHz band has a similar design. The load-bearing traverse is made of a wooden bar 370 cm long and a section of 2.5x5 cm.The height of the bar gradually decreases towards the ends to 1.5 cm.

The length of the reflex frame is 711 mm, and the active frame is 676 mm. Both frames are made of copper wire with a diameter

2.5 mm. The directors are made of wire with a diameter of 3 mm. Other dimensions are shown in fig. 36.

The antenna is powered by a coaxial cable with a characteristic impedance of 50 Ohm without a balun. In principle, this antenna can be used for the 1296 MHz range, while the wire diameter and all other dimensions should be reduced by 3 times.

Fig. 36. Fifteen-element Quagi antenna for 432 MHz band.

Of the antennas specially designed for the 1296 MHz range, the antenna proposed by the British VHF G3JVL is of interest. The antenna is a "wave channel" with ring vibrato

rami, a kind of multi-element loop antenna. The antenna contains 28 elements, including an additional reflector made of aluminum mesh and 27 ring vibrators. The main reflector and all directors are made of aluminum strips 4.8 mm wide and 0.7 mm thick.

At the ends of the strips, holes are drilled for an M3 screw. The distance between the centers of the hole is 246 mm for the reflector, 210 mm for the first 11 directors and 203 mm for the remaining directors. Then the strips are rolled up into a ring and screwed to a supporting duralumin tube with a diameter of 12-15 mm. The distances between the elements are shown in Fig.

37. The dimensions of the additional reflector are shown in Fig. 38, a.

Fig. 37. Twenty-eight-element antenna for 1296 MHz range, distances to elements are measured from an additional reflector.

Fig. 38. Antenna for 1296 MHz band.

The design of the active element is shown in Fig. 38.6. Unlike other elements, the active frame is made from a copper strip. Frame perimeter 235 mm.

The frame is attached to the support tube using a MB threaded bolt. A thin PTFE insulated cable is passed through a drilled hole along the bolt axis. In the middle of the strip, from which the active frame is made, there is also a hole drilled for the cable. The frame is soldered to the bolt head. The cable sheath is also soldered to the head of the bolt.

A thin cable with increased attenuation should be as short as possible. It ends with a high frequency connector to which the main feeder is connected. Alternatively, the thicker cable is passed through the mounting bolt, but through the hole drilled in the support tube behind the active frame.

In this case, it is also necessary to ensure contact of the cable sheath with the base of the frame.

Antenna descriptions deliberately omit gain data. The fact is that accurate measurement of antenna gain is difficult enough, requiring special conditions. As a result, various data often appear in the amateur radio literature.

So, the figure given by the author of the antenna described above for the 1296 MHz range seems to be somewhat overestimated - 20 dB. The data given for the Quagi antenna looks more realistic - 12 dB for an 8-element antenna and 15 dB for a 15-element antenna.

Zhutyaev S.G. Amateur VHF radio station, 1981.

First, why is the word "tuning" of the antenna in quotation marks. Suppose you made an antenna "according to concepts" with all the bells and whistles, boxes, plumbing, etc., put to it in your opinion, and if the SWR is "not the same", for you there is nothing easier than to move something, cut off, instruct and etc. in the antenna itself. Also by concepts, because somewhere someone wrote about what, where and how to move so that the SWR was "one". However, in a VC antenna, for example with a split vibrator, there are only three general parameters: diameter, length and position of elements. The accuracy of their observance is quite sufficient for its compliance with the model and coordinated work with the cable. This means that if the SWR is "wrong", it is not about them and move, cut, instruct the elements, focusing on the SWR, i.e. by agreement, it means to introduce into the antenna one more "nontakness" of the opposite sign, if only "it eats all the power", but where and how it radiates, we do not know and sleep peacefully. Something like "tuning" the TV for power consumption without looking at the screen.

So, the antenna is done, but the SWR is "wrong". Let's put the hacksaw aside and see why.
♣- If the antenna is made according to pictures and dimensions in reputable publications, it is advisable to get an objective idea of ​​it before cutting it. Promises like "R input 60 Ohm, 11.5 dB gain, high efficiency, no special settings" may turn out to be a deception or delusion of the author and agree it (Rothammel, vol. 2, p. 70, Quagi antenna) or it is impossible to achieve the promised parameters in principle (Avrika Grabli. Magazine "OST". may 1997, pp. 58, 59). Therefore, it is better to look at it in the calculation program before making it. It will take less time than fruitless attempts to reanimate scrap metal.

It is likely that the reason is outside the antenna, because in addition to it, the SWR meter itself, the connecting cable and the environment of the antenna are involved in the measurement.
♣- A strong influence on the SWR, up to 2 or more, can be exerted by the environment of the antenna. These are objects located in the near zone (up to 1λ from the size of the antenna) that are opaque for the operating frequency (with strong reflection or absorption), including a cable that was unsuccessfully diverted from the vibrator, and reflectors in the alignment of the main lobe at a distance λ closer than the antenna gain in db. This effect can be avoided by taking measurements in an open area, pointing the antenna towards the sky. If possible, make the traverse for the time of manufacture and testing longer than the reflector. At the first stage of checking the antenna, it will be possible to hold it by the shank and rotate and change direction, make sure that the SWR changes by no more than 0.1. This suggests that the influence of the antenna environment is within acceptable limits, otherwise it is necessary to change the position to one that is more free from such influence, where you can continue working with the antenna, pointing it up and securing it to the shank.
♣- A 10% VSWR meter error will give you a VSWR of 1.1. The MFJ 269 has such an error. Therefore, a SWR of 1.1 and below should be taken as an inevitable tolerance for the measurement error, although it is not difficult to agree, or rather to mismatch the antenna for this error up to SWR 1.00.
♣In addition to the error, there is another factor affecting the readings, these are harmonics in the SWR meter signal. For MFJ, they are -26 dB or 5% of the level of the fundamental frequency, for T 100 -30 dB or 3%. Moreover, the AA 600 has a rectangular output signal (meander), in which the level of the 2nd and 3rd harmonics is about 30% of the fundamental frequency. At a reference resistive load, they all together show a VSWR of 1.00. And for a real antenna it is unlikely that its SWR is also 1.0 at double and triple frequencies, rather the harmonics will be fully reflected and with an actual antenna SWR of 1.0 at the fundamental frequency, MFJ and T100 can and should show no better than 1.05, and AA 600 is not better than 1.5. Otherwise, it is necessary either to consider their readings unreliable, or the attenuation of the cable at the harmonics is large, that their direct and reflected power is lost in it.
♣- Tolerance of the wave resistance of the cable according to GOST + -4%. The actually measured deviations of the wave impedances of RG8x, RG58 cables and other products of the free market are up to 25%. These deviations will give you a VSWR of up to 1.08 for antennas with Soviet cables and up to 1.5 with bourgeois brands. This can be avoided by using a tested piece of cable with a minimum possible length for testing the antenna, but a multiple of half the wavelength, taking into account K shortening, which in this case will work as a half-wave repeater in a sufficiently wide frequency band.
The idea of ​​which SWR of a normal antenna the SWR meter will show with an unfavorable combination of these factors can be obtained by multiplying the extreme values ​​of each of them: 1.1x1.5x2.0 = SWR 3.3. (With the same degree of probability, you can get a SWR of 1.0 for an antenna with a SWR = 3.3 with a combination of these factors "favorable" for it.)

There are still three or four steps left to the antenna. In almost every design, except for the VC antenna itself, i.e. elements of a certain shape, length and position, there are devices that are difficult or impossible to include in the model, and therefore taking into account their influence and ways of solving remain the most difficult and controversial issues:
R antenna cable matching device (transformer)
Current cut-off device on the outside of the braid. (1/4 λ glass, ferrite, etc.)
A device for connecting a cable to an antenna, if you can call it a pigtail and a central core between the cable and the antenna.
Device for fixing elements in position and position according to the model (traverse and fasteners)
I will not repeat myself. More than half of the material on the pages of the site is devoted to how to minimize their influence and avoid mistakes in the manufacture of antennas.

There is only one reason for the discrepancy between the SWR of the antenna and its model.
This is a model, or rather errors in it. Sharp (< 45°) углы между проводами, близкорасположенные провода и сегменты в них длинее, чем расстояние между проводами, толстые провода и сегменты в них короче, чем их диаметр, - самые распространенные ошибки. It is advisable to make sure that there are no errors in the model before making the antenna. If you yourself delve into the subtleties of segmentation, etc. while it's difficult, send the file by e-mail me or my friend who has mastered the program.

If everything that is said above has been observed, then I dare to assure you that after the careful manufacture of even the most narrow-band and error-sensitive antenna, you will not need to saw, guide and move anything in it. All that remains is to install it on a mast or stack and route the cable so that they have minimal effect on the antenna.
Antenna can be tuned only under the control of all the parameters for which it is responsible. This is primarily the directional diagram (and its derivative - gain). This setting is a difficult task even for professionals at a professional training ground. Hence, a simple conclusion and solution is to abandon in a real antenna what is not modeled in the model, but affects its parameters or to reduce it to a minimum. Then you can be sure that even "the right one" SWR is not a randomly zeroed sum of "non-equalities" of different signs, but a sign of correspondence of antenna parameters other than SWR to those parameters that were achieved in the model.

You can and should tune an antenna that has to be installed in conditions that are difficult or impossible to take into account or simulate, an antenna for HF bands, next to which is the ground, wires, etc. Moreover, already at 21 MHz, and even more so at 28 MHz, their influence easy to reduce or eliminate altogether. And on any VHF range, such an influence is unacceptable, because it distorts the diagram and it is already meaningless to tune something in the antenna itself "under SWR 1.0". It is necessary to search and find a mistake, there is no other choice.

A short time ago, mostly home-made equipment was used to work on the 145 MHz band. VHF transverters were popular among radio amateurs, many of which were comparable in size to the transceiver used with it. Radio amateurs converted decommissioned industrial VHF-type "Palma" radio stations to the amateur VHF range of 145 MHz, receiving a radio station operating on several channels. Then "Viola" became available to radio amateurs, and later "Mayaki" operating on forty channels. These radio stations then looked fantastic in their capabilities!

Currently, it is relatively inexpensive to purchase multichannel portable VHF transceivers of world famous companies - " YAESU "," KENWOOD "," ALINCO ", Which in terms of their parameters and usability significantly surpass both the home-made equipment of the 145 MHz range, and the converted industrial equipment -" Palmy "," Mayaki "," Viola ".

But to work through a repeater from home, office, while driving when working from a car, an antenna is needed that is more effective than the "rubber band" used in conjunction with a portable radio station. When using a stationary "branded" VHF station, it is often advisable to use a homemade VHF antenna with it, since a decent "branded" outdoor antenna of the 145 MHz range is not cheap.

This material is devoted to the manufacture of simple homemade antennas suitable for use with stationary and portable VHF radio stations.

Features of 145 MHz antennas

Due to the fact that for the manufacture of antennas in the 145 MHz range, a thick wire is usually used - with a diameter of 1 to 10 mm (sometimes thicker vibrators are used, especially in commercial antennas), then antennas in the 145 MHz range are broadband. This often makes it possible, when making an antenna exactly according to the specified dimensions, to do without its additional tuning to the 145 MHz range.

For tuning antennas of the range 145 MHz you must have a SWR - meter. It could be like homemade device and industrial production. On the 145 MHz band, radio amateurs practically do not use bridge antenna resistance meters, due to the apparent complexity of their correct manufacture. Although with careful manufacture of the bridge meter and, therefore, its correct operation in this range, it is possible to accurately determine the input impedance of the VHF antennas. But even using only the SWR - a through-type meter, it is quite possible to tune homemade VHF antennas. The power of 0.5 W, which is provided by imported portable radio stations in the " LOW "And domestic portable VHF radio stations of the" Dnepr "type,"Viola", "VEBR" are quite enough for the operation of many types of SWR meters. Mode " LOW »Allows you to tune antennas without fear of failure of the output stage of the radio station at any antenna input impedance.

Before tuning the VHF antenna, it is advisable to make sure that the SWR meter readings are correct. It is a good idea to have two SWR meters rated for 50 and 75 ohm transmission paths. When tuning VHF antennas, it is desirable to have a control antenna, which can be either a "rubber band" from a portable radio station or a homemade quarter-wave pin. When tuning the antenna, the level of the field strength created by the tuned antenna is measured relative to the reference one. This makes it possible to judge the comparative efficiency of the tunable antenna. Of course, if a standard calibrated field strength meter is used in the measurements, an accurate estimate of the antenna performance can be obtained. When using a calibrated field meter, it is easy to remove the antenna directional pattern. But even using home-made field strength meters during measurements and having obtained only a qualitative picture of the distribution of the electromagnetic field strength, it is quite possible to draw a conclusion about the efficiency of the tuned antenna and approximately estimate its directional pattern.

Consider the practical designs of VHF antennas.

Simple antennas

The simplest outdoor VHF antenna (Fig. 1) can be made using an antenna that works in conjunction with a portable radio station. On the window frame from the outside (Fig. 2) or from the inside, a metal corner is attached to an extension wooden bar, in the center of which there is a socket for connecting this antenna. It is necessary to strive to ensure that the coaxial cable leading to the antenna was the minimum required length. Along the edges of the corner, 4 counterweights 50 cm long are attached. It is necessary to ensure good electrical contact of the counterweights, the antenna connector with the metal corner. The shortened twisted antenna of the radio station has an input impedance in the range of 30-40 ohms, so that a coaxial cable with a characteristic impedance of 50 ohms can be used to power it. With the help of the angle of inclination of the counterweights, it is possible to change the input impedance of the antenna within certain limits, and, therefore, to match the antenna with the coaxial cable. Instead of a proprietary "rubber band", you can temporarily use an antenna made of a copper wire with a diameter of 1-2 mm and a length of 48 cm, which is inserted into the antenna socket with its sharply sharpened end.

Figure 1 Simple Outdoor VHF Antenna

Figure 2 Construction of a simple outdoor VHF antenna

The VHF antenna, made of a coaxial cable with the outer sheath removed, works reliably. The cable is terminated in the HF-connector similar to the connector of the "proprietary" antenna (Fig. 3). The length of the coaxial cable used for the manufacture of the antenna is 48 cm. Such an antenna can be used in conjunction with a portable radio station instead of a broken or lost standard antenna.

Figure 3 Simple homemade VHF antenna

For the quick manufacture of an external VHF antenna, you can use a connecting coaxial cable 2-3 meters long, which is terminated with connectors corresponding to the antenna jack of the radio station and antenna. The antenna can be connected to such a piece of cable using a high-frequency tee (Fig. 4). In this case, a “rubber band” antenna is connected from one end of the tee, and 50 cm counterweights are screwed on the other end of the tee, or another type of radio technical “ground” for the VHF antenna is connected through the connector.

Figure 4 Simple remote VHF antenna

Homemade portable radio antennas

If you lose or break the standard antenna of a portable radio station, you can make a homemade twisted VHF antenna. For this, a base is used - polyethylene insulation of a coaxial cable with a diameter of 7-12 mm and a length of 10-15 cm, on which initially 50 cm of a copper wire with a diameter of 1-1.5 mm is wound. It is very convenient to use a frequency response meter to tune a twisted antenna, but you can also use an ordinary SWR meter. Initially, the resonant frequency of the assembled antenna is determined, then, by biting off part of the turns, shifting, moving apart the turns of the antenna, the twisted antenna is tuned to resonance at 145 MHz.

This procedure is not very complicated, and by tuning 2-3 twisted antennas, the radio amateur can tune new twisted antennas in literally 5-10 minutes, of course, if the above devices are available. After tuning the antenna, it is necessary to fix the turns either with electrical tape, or using a cambric soaked in acetone, or usingheat-shrinkable tube. After fixing the turns, it is necessary to check the frequency of the antenna again and, if necessary, adjust it using the upper turns.

It should be noted that in "branded" shortened twisted antennas, heat-shrinkable tubes are used to fix the antenna conductor.

Half-wave field antenna

For quarter-wave antennas to work effectively, multiple quarter-wave counterweights must be used. This complicates the design for a field quarter-wave antenna, which must be spaced out in relation to the VHF transceiver. In this case, you can use a VHF antenna with an electrical length of λ / 2, which does not require counterweights for its operation, and provides a directional pattern pressed to the ground and ease of installation. For an antenna with an electrical length of λ / 2, there is a problem of matching its high input impedance with a low characteristic impedance coaxial cable. An antenna λ / 2 long and 1 mm in diameter will have an input impedance at 145 MHz of about 1000 ohms. Matching using a quarter-wave resonator, which is optimal in this case, is not always convenient in practice, since it requires the selection of points for connecting the coaxial cable to the resonator for its effective operation and precise tuning of the antenna pin to resonance. The dimensions of the resonator for the 145 MHz range are also relatively large. The destabilizing factors on the antenna when it is matched using a resonator will be especially pronounced.

However, at low powers supplied to the antenna, quite satisfactory matching can be achieved using a P - loop, similarly to how it is described in the literature. A diagram of a half-wave antenna and its matching device is shown in Fig. 5. The length of the antenna rod is chosen slightly shorter or longer than the length λ / 2. This is necessary so that even with a small difference in the electrical length of the antenna from λ / 2, the active resistance of the antenna impedance decreases noticeably, and its reactive part at the initial stage increases insignificantly. As a result, matching with the help of the P - contour of such a shortened antenna is possible with greater efficiency than matching an antenna with a length of exactly λ / 2. It is preferable to use an antenna with a length slightly longer than λ / 2.

Figure 5 Coordination of the VHF antenna using the P - loop

Air trimming capacitors of the KPVM-1 type were used in the matching device. Coil L 1 contains 5 turns of a silver-plated wire with a diameter of 1 mm, wound on a mandrel with a diameter of 6 mm and a pitch of 2 mm.

Antenna tuning is not difficult. By including a SWR meter into the cable path of the antenna and at the same time measuring the level of the field strength created by the antenna by changing the capacitance of variable capacitors C1 and C2, compressing-stretching the turns of the coil L 1 achieve the minimum readings of the SWR meter and, accordingly, the maximum readings of the field strength meter. If these two maxima do not coincide, it is necessary to slightly change the length of the antenna, and repeat its adjustment again.

The matching device was placed in a case soldered from foil-clad fiberglass with dimensions of 50 * 30 * 20 mm. When working from a stationary workstation of a radio amateur, the antenna can be placed in the window opening. When working in the field, the antenna can be suspended from the upper end from a tree using a fishing line, as shown in fig. 6. A 50-ohm coaxial cable can be used to power the antenna. The use of a 75-ohm coaxial cable will slightly increase the efficiency of the antenna matching device, but at the same time, it will require tuning the output stage of the radio station to operate on a 75-ohm load.

Figure 6 Installing Antenna for Field Operation

Foil Window Antennas

On the basis of the adhesive foil used in security alarm systems, very simple designs of VHF window antennas can be built. This foil can already be purchased with an adhesive base. Then, having freed one side of the foil from the protective layer, it is enough just to press it against the glass and the foil is instantly reliably glued. Foil without an adhesive base can be glued to glass using varnish or glue like "Moment". But for this you need to have some skill. The foil can even be secured to the window with adhesive tape.

With proper training, it is quite possible to make a good soldered connection between the center conductor and the braid of the coaxial cable with aluminum foil. Based on personal experience, each type of such foil requires its own flux for soldering. Some types of foil solder well even using rosin alone, some can be soldered with soldering grease, other types of foil require the use of active fluxes. The flux should be tested on the specific type of foil used to make the antenna well in advance of installation.

Good results are obtained by using a foil-clad fiberglass substrate for soldering and fixing the foil, as shown in Fig. 7. A piece of foil-clad fiberglass is glued to the glass using Moment glue, the antenna foil is soldered to the edges of the foil, the coaxial cable cores are soldered to the copper foil of the fiberglass at a short distance from the foil. After soldering, the connection must be protected with a moisture-resistant varnish or glue. Otherwise, this connection may corrode.

Figure 7 Connecting Antenna Foil to Coaxial Cable

Let us examine the practical designs of foil-based window antennas.

Vertical window dipole antenna

A diagram of a vertical dipole window VHF antenna based on a foil is shown in Fig. eight.

Figure 8 Windowed vertical dipole VHF antenna

The quarter-wave post and counterweight are positioned at an angle of 135 ° so that the input impedance of the antenna system approaches 50 ohms. This makes it possible to use a coaxial cable with a characteristic impedance of 50 Ohm to power the antenna and use the antenna in conjunction with portable radio stations, the output stage of which has such an input impedance. The coaxial cable should run perpendicular to the antenna over the glass for as long as possible.

Foil frame antenna

A frame window VHF antenna, shown in Fig. 2, will work more efficiently than a dipole vertical antenna. 9. When the antenna is fed from the lateral angle, the maximum of the radiated polarization is in the vertical plane, when the antenna is fed in the lower angle, the maximum of the radiated polarization is in the horizontal plane. But at any position of the power points, the antenna emits a radio wave, with combined polarization, both with vertical and horizontal. This circumstance is very favorable for communication with portable and mobile radio stations, the position of the antennas of which will change during movement.

Figure 9 VHF window frame antenna

The input impedance of the window loop antenna is 110 ohms. To match this impedance with a coaxial cable with a characteristic impedance of 50 Ohm, a quarter-wave section ofcoaxial cable with a characteristic impedance of 75 ohms. The cable should run perpendicular to the antenna axis for as long as possible. The loop antenna has a gain of about 2 dB higher than a dipole window antenna.

When performing window antennas made of foil with a width of 6-20 mm, they do not require tuning and operate in the frequency range significantlywider than the amateur band of 145 MHz. If the obtained resonant frequency of the antennas is lower than the required one, then the dipole can be tuned by symmetrically cutting off the foil from its ends. The loop antenna can be tuned using a jumper made from the same foil used to make the antenna. The foil closes the antenna web in the corner, opposite the power points. Once configured, contact between the jumper and the antenna can be made either by soldering or using adhesive tape. Such adhesive tape should press the jumper firmly against the antenna web in order to ensure reliable electrical contact with it.

Antennas made of foil can be supplied with significant power levels - up to 100 watts or more.

Outdoor vertical antenna

When placing the antenna outside the room, the question always arises about protecting the opening of the coaxial cable from atmospheric influences, about using a high-quality antenna support insulator, moisture-resistant wire for antennas, etc. These problems can be solved by installing a protected outdoor VHF antenna. The design of such an antenna is shown in Fig. 10.

Figure 10 Protected outdoor VHF antenna

A hole is made in the center of a 1 meter long plastic water pipe, into which the coaxial cable can fit tightly. Then the cable is threaded there, protrudes out of the pipe, is exposed at a distance of 48 cm, the cable shield is twisted and soldered at a length of 48 cm. The cable with the antenna is put back into the pipe. Standard plugs are put on the top and bottom of the pipe. It is not difficult to waterproof the hole where the coaxial cable enters. This can be done with automotive silicone or a fast curing automotive epoxy. As a result, we get a beautiful, moisture-insulated protected antenna that can work for many years under the influence of atmospheric influences.

To fix the vibrator and the antenna counterweight inside, you can use 1-2 cardboard or plastic washers tightly put on the antenna vibrators. The antenna tube can be installed on a window frame, on a non-metallic mast, or in any other convenient location.

Simple coaxial collinear antenna

A simple collinear coaxial VHF antenna can be made of coaxial cable. A piece of water pipe can be used to protect this antenna from the weather as described in the previous paragraph. The design of a collinear coaxial VHF antenna is shown in Fig. eleven.

Figure 11 Simple collinear VHF antenna

The antenna provides a theoretical gain of at least 3 dB more than a quarter-wave vertical. It does not need counterweights for its operation (although their presence improves the performance of the antenna) and provides a flattened radiation pattern to the horizon. Descriptionsuch an antenna has repeatedly appeared on the pages of domestic and foreign radio amateur literature, but the most successful description was presented in the literature.

Antenna dimensions in fig. 11 are in centimeters for coaxial cable with a shortening factor of 0.66. Most coaxial cables with polyethylene insulation have such a factor of shortening. The dimensions of the matching loop are shown in Fig. 12. Without using this loop, the VSWR of the antenna system can exceed 1.7. If the antenna turned out to be tuned below the 145 MHz range, it is necessary to slightly shorten the upper section, if higher, then lengthen it. Of course, the optimal tuning is possible by proportional shortening-lengthening of all parts of the antenna, but this is difficult to do in an amateur radio environment.

Figure 12 Dimensions of the matching loop

Despite the large size of the plastic pipe required to protect this antenna from atmospheric influences, the use of a collinear antenna of this design is quite reasonable. The antenna can be moved away from the building using wooden battens, as shown in fig. 13. The antenna can withstand significant power input to it up to 100 watts or more and can be used in conjunction with both stationary and portable VHF radio stations. The use of such an antenna in conjunction with low-power portable radio stations will give the greatest effect.

Figure 13 Installing a Collinear Antenna

Simple collinear antenna

This antenna was assembled by me similarly to the construction of a car remote antenna used in a cellular radiotelephone. To convert it to the amateur band of 145 MHz, I proportionally changed all dimensions of the "telephone" antenna. As a result of this, an antenna was obtained, the diagram of which is shown in Fig. 14. The antenna provides a horizontal radiation pattern and a theoretical gain of at least 2 dB over a simple quarter-wave rod. A coaxial cable with a characteristic impedance of 50 Ohm was used to power the antenna.

Figure 14 Simple collinear antenna

A practical antenna design is shown in Fig. 15. The antenna was made from a single piece of copper wire with a diameter of 1mm. Coil L 1 contained 1 meter of this wire, wound on a mandrel with a diameter of 18 mm, the distance between the turns was 3 mm. When making a design exactly to the dimensions, the antenna practically does not require adjustment. It may be necessary to slightly tune the antenna by squeezing-stretching the turns of the coil to achieve a minimum SWR. The antenna was housed in a plastic water pipe. Inside the pipe, the antenna wire was fixed with pieces of foam. Four quarter-wave counterweights were installed at the lower end of the pipe. They were threaded and fastened to a plastic pipe with nuts. Counterweights can be 2-4 mm in diameterdepending on the ability to cut threads on them. For their manufacture, you can use copper, brass, or bronze wire.

Figure 15 Construction of a simple collinear antenna

The antenna can be installed on wooden rails on the balcony (as shown in fig. 13). This antenna can withstand significant levels of power input.

This antenna can be thought of as a shortened HF antenna with a center extension coil. Indeed, the antenna resonance measured with a bridge resistance meter in the HF range turned out to be in the frequency region of 27.5 MHz. Obviously, by varying the diameter of the coil and its length, but at the same time maintaining the length of the winding wire, it is possible to ensure that the antenna works both in the VHF range of 145 MHz and in one of the HF ranges - 12 or 10 meters. To operate on the HF bands, four λ / 4 counterweights for the selected HF band must be connected to the antenna. This dual use of the antenna will make it even more versatile.

Experimental 5/8 wave antenna

When experimenting with radio stations of the 145 MHz range, it is often necessary to connect the antenna under test to its output stage in order to check the operation of the radio station's receive path or adjust the output stage of the transmitter. For thosegoals by me for a long time a simple 5/8 - wave VHF antenna is used, the description of which was given in the literature.

This antenna consists of a section of copper wire with a diameter of 3 mm, which is connected at one end to an extension coil and the other to a tuning section. At the end of the wire connected to the coil, a thread is cut, and at the other end, a tuning section made of copper wire with a diameter of 1 mm is soldered. The antenna is matched with a coaxial cable with a characteristic impedance of 50 or 75 Ohm by connecting to different turns of the coil, and may be a slight shortening of the tuning section. The antenna diagram is shown in Fig. 16. antenna design is shown in fig. 17.

Figure 16 Scheme of a simple 5/8 - wave VHF antenna

Figure 17 Construction of a simple 5/8 - wave VHF antenna

The coil is made on a plexiglass cylinder with a diameter of 19 mm and a length of 95 mm. At the ends of the cylinder, a thread is made into which the antenna vibrator is screwed on one side, and on the other side it is screwed to a piece of foil-clad fiberglass with dimensions of 20 * 30 cm, which serves as the “ground” of the antenna. On the back side, a magnet was glued to it fromthe old speaker, as a result of which the antenna can be attached to the windowsill, to the radiator, to other iron objects.

The coil contains 10.5 turns of wire with a diameter of 1 mm. The coil wire is evenly spaced over the frame. The coaxial cable is tapped from the fourth turn from the grounded end. The antenna vibrator is screwed into the coil, a contact lamella is inserted under it, to which the "hot" end of the extension coil is soldered. The lower end of the coil is soldered to the antenna ground foil. The antenna provides a SWR in the cable no worse than 1: 1.3. The antenna is tuned by shortening its upper part with pliers, which is initially slightly longer than necessary.

I have experimented with installing this antenna on a window pane. In this case, a vibrator with an original length of 125 centimeters made of aluminum foil was glued to the center of the window. The extension reel was used the same and was installed on the window frame. The counterweights were made of foil. The ends of the antenna and counterweights were curved slightly to fit on the window pane. Window 5/8 - wave VHF antenna is shown in Fig. 18. The antenna is easily tuned into resonance by gradually shortening the vibrator foil using a blade, and by gradually switching the coil turns to minimize SWR. The window antenna does not spoil the interior of the room and can be used as a permanent antenna for operating on the 145 MHz band from home or office.

Figure 18 Window 5/8 - wave VHF antenna

Efficient Portable Radio Antenna

In the case when communication using a standard "rubber" is not possible, you can use a half-wave antenna. It does not require "ground" for its work and when working over long distances it gives a gain in comparison with a standard "rubber band" up to 10 dB. These are quite realistic numbers, given that the physical length of a half-wave antenna is almost 10 times longer than the "rubber band".

The half-wave antenna is supplied with voltage and has a high input impedance that can reach 1000 ohms. Therefore, this antenna requires a matching device when used with a radio with a 50 ohm output. One of the variants of the P-loop matching device has already been described in this chapter. Therefore, for a change, for this antenna, we will consider the use of another matching device, made on a parallel circuit. In terms of their efficiency, these matching devices are approximately equal. A diagram of a half-wave VHF antenna together with a matching device on a parallel circuit is shown in Fig. nineteen.

Figure 19 Half-wave VHF antenna with matching device

The coil of the loop contains 5 turns of copper silver-plated wire with a diameter of 0.8 mm, wound on a mandrel with a diameter of 7 mm along a length of 8 mm. Tuning the matching device consists in tuning using a variable capacitor C1 of the circuit L 1C1 into resonance, with the help of a variable capacitor C2, the connection of the circuit with the transmitter output is regulated. Initially, the capacitor is connected in the third turn of the coil from its grounded end. Variable capacitors C1 and C2must be with an air dielectric.

It is advisable to use a telescopic antenna for the antenna vibrator. This will make it possible to carry the half-wave antenna in a compact folded state. It also makes it easier to tune the antenna together with a real transceiver. During the initial tuning of the antenna, its length is 100 cm. During the tuning process, this length can be slightly adjusted for better antenna performance. It is advisable to make appropriate marks on the antenna in order to subsequently install the antenna from its folded position to the resonant length immediately. The box where the matching device is located must be made of plastic to reduce the coil capacityon the "ground" can be made of foil-clad fiberglass. This depends on the actual operating conditions of the antenna.

The antenna is tuned using a field strength indicator. With the help of the SWR meter, tuning the antenna is advisable only if it works not on the body of the radio station, but when using an extension coaxial cable together with it.

When the antenna is working twice on the radio station body and using an extension coaxial cable, two marks are made on the antenna pin, one corresponding to the maximum field strength level when the antenna is operating on the radio station body, and the other risk corresponds to the minimum SWR when using an extension coaxial cable in conjunction with the antenna. Usually these two marks are slightly different.

Vertical continuous gamma-matched antennas

Vertical antennas made of a whole vibrator are wind-resistant, easy to install, and take up little space. For their implementation, you can use copper tubes, aluminum power electrical wire with a diameter of 6-20 mm. These antennas can be easily matched with a coaxial cable with a characteristic impedance of both 50 and 75 ohms.

An inseparable half-wave VHF antenna, the design of which is shown in Fig. 20. Gamma matching is used to power it through the coaxial cable. The material from which the antenna vibrator is made and the gamma matching must be the same, for example, copper or aluminum. Due to mutual electrochemical corrosion of many pairs of materials, it is unacceptable to use different metals for antenna and gamma matching.

Figure 20 Continuous half-wave VHF antenna

If a bare copper tube is used to make the antenna, then it is advisable to adjust the antenna gamma matching using a closing jumper as shown in Fig. 21. In this case, the surface of the pin and the conductor of the gamma matching is carefully cleaned and using a clamp of bare wire as shown in fig. 21a achieve the minimum VSWR in the coaxial power cable of the antenna. Then, in this place, the gamma matching wire is slightly flattened, drilled and connected with a screw to the antenna sheet, as shown in Fig. 21b. Soldering is also possible.

Figure 21 Copper antenna gamma matching

If an aluminum wire is used for the antenna from a power electrical cable in plastic insulation, then it is advisable to leave this insulation to prevent corrosion of the aluminum wire with acid rain, which is inevitable in urban conditions. In this case, the antenna gamma matching is adjusted using a variable capacitor, as shown in Fig. 22. This variable capacitor must be carefully protected from moisture. If it is not possible to achieve the SWR in the cable less than 1.5, then the length of the gamma matching must be reduced and the setting repeated again.

Figure 22 Setting the gamma - matching of the aluminum copper antenna

With sufficient space and materials, a continuous VHF vertical wave antenna can be installed. The wave antenna works more efficiently than the half-wave antenna shown in Fig. 20. A wave antenna provides a more horizontal radiation pattern than a half-wave antenna. You can match the wave antenna using the methods shown in Fig. 21 and 22. The design of the wave antenna is shown in fig. 23,

Figure 23 Continuous vertical wave VHF antenna

When performing these antennas, it is desirable that the coaxial power cable is at least 2 meters perpendicular to the antenna. The use of a balun together with a continuous antenna will increase the efficiency of its operation. When using a balun, use symmetrical gamma matching. The balun connection is shown in fig. 24.

Figure 24 Connecting the balun to a continuous antenna

Any other known balun can also be used as the antenna balun. When placing the antenna near conductive objects, it may be necessary to slightly reduce the length of the antenna due to the influence of these objects on it.

Round VHF antenna

If the placement in space of the vertical antennas shown in Fig. 20 and fig. 23 in their traditional vertical position is difficult, then they can be placed by rolling the antenna web in a circle. The position of the half-wave antenna shown in Fig. 20 in the "round" version is shown in fig. 25, and the wave antenna shown in Fig. 23 in Fig. 26. In this position, the antenna provides combined vertical and horizontal polarization, which is favorable for communications with mobile and portable radios. Although, theoretically, the level of vertical polarization will be higher with lateral feeding of circular VHF antennas, but in practice this difference is not very noticeable, and the lateral feeding of the antenna complicates its installation. The side power supply of the circular antenna is shown in Fig. 27.

Figure 25 Continuous circular vertical half-wave VHF antenna

Figure 26 Continuous circular vertical wave VHF antenna

Figure 27 Lateral power supply of circular VHF antennas

The round VHF antenna can be placed indoors, for example, between window frames, or outdoors, on a balcony or on a roof. When placing a circular antenna in the horizontal plane, we obtain a circular radiation pattern in the horizontal plane and the operation of an antenna with horizontal polarization. This may be necessary in some cases when conducting amateur radio communications.

Passive "amplifier" of the portable station

When testing portable radios or working with them, sometimes there is not enough power for reliable communication. I made a passive "amplifier" for portable VHF stations. A passive "amplifier" can add up to 2-3 dB to the signal of a radio station on the air. This is often enough to reliably open the squelch of the correspondent station and ensure reliable operation. The design of the passive "amplifier" is shown in Fig. 28.

Figure 28 Passive "amplifier"

The passive "amplifier" is a large enough tinned coffee can (the bigger the better). A connector is inserted into the bottom of the can, similar to the antenna connector of a radio station, and a connector for connecting to the antenna jack is sealed into the lid of the can. 4 counterweights 48 cm long are soldered to the bank. When working with a radio station, this "amplifier" is switched on between the standard antenna and the radio station. Due to the more effective "ground" and there is an increase in the place of reception of the strength of the emitted signal. Other antennas can be used in conjunction with this "amplifier", for example, a λ / 4 pin made of copper wire, simply inserted into the antenna socket.

Broadband survey antenna

Many imported portable radios provide reception not only in the amateur band of 145 MHz, but also in the survey ranges of 130-150 MHz or 140-160 MHz. In this case, for successful reception in survey bands, on which a twisted antenna tuned to 145 MHz does not work effectively, you can use a broadband VHF antenna. The antenna diagram is shown in Fig. 29 and dimensions for different ranges of operation are given in table. one.

Figure 29 Broadband VHF vibrator

Table 1 Dimensions of a wideband VHF antenna

Table 1

To work with the antenna, you can use a coaxial cable with a characteristic impedance of 50 Ohm. The antenna can be made of foil and glued to the window. You can make the antenna fabric from an aluminum sheet, or by printing on a piece of foil-clad fiberglass of suitable dimensions. This antenna can transmit and receive in the specified frequency ranges with high efficiency.

Zigzag antenna

Some service VHF long-distance radio stations use antenna arrays consisting of zigzag antennas. Radio amateurs can also try to use elements of such an antenna system for their work. The view of an elementary zigzag antenna included in the design of a complex VHF antenna is shown in Fig. thirty.

Figure 30 Elementary zigzag antenna

The zigzag elementary antenna consists of a half-wave dipole antenna that supplies voltage to the half-wave vibrators. In real antennas, up to five such half-wave vibrators are used. Such an antenna has a narrow directional pattern pressed to the horizon. The type of polarization emitted by the antenna is combined - vertical and horizontal. It is advisable to use a balun for antenna operation.

In antennas used in service communication stations, a reflector made of a metal mesh is usually placed behind elementary zigzag antennas. The reflector provides one-way directivity of the antenna. Depending on the number of vibrators included in the antenna and the number of zigzag antennas included together, the required antenna gain can be obtained.

Radio amateurs practically do not use such antennas, although they are easy to implement for the amateur VHF bands of 145 and 430 MHz. For the manufacture of the antenna sheet, you can use an aluminum wire with a diameter of 4-12 mm from a power electrical cable. In the domestic literature, a description of such an antenna, for which a rigid coaxial cable was used, was given in the literature.

Antenna Kharchenko in the range of 145 MHz

Kharchenko's antenna is widely used in Russia for television reception and in service radio communications. But radio amateurs use it to work on the 145 MHz band. This antenna is one of the few that works very efficiently and requires little or no tuning. The diagram of Kharchenko's antenna is shown in Fig. 31.

Figure 31 Kharchenko antenna

Both 50 and 75 ohm coaxial cables can be used for antenna operation. The antenna is broadband, operates in a frequency band of at least 10 MHz on a range of 145 MHz. To create a one-sided radiation pattern, a metal mesh is used behind the antenna located at a distance of (0.17-0.22) λ.

The Kharchenko antenna provides a width of the beam pattern in the vertical and horizontal planes close to 60 o. To further narrow the radiation pattern, passive elements are used in the form of vibrators with a length of 0.45λ, located at a distance of 0.2λ from the diagonal of the square of the frames. To create a narrow radiation pattern and increase the gain of the antenna system, several combined antennas are used.

Directional loop antennas of 145 MHz range

One of the most popular directional antennas for operation in the 145 MHz band are loop antennas. The most common two-element loop antennas on the 145 MHz band. In this case, an optimal cost / quality ratio is obtained. The diagram of a two-element loop antenna as well as the dimensions of the perimeter of the reflector and the active element are shown in Fig. 32.

Figure 32 VHF loop antenna

The antenna elements can be made not only in the form of a square, but also in the form of a circle, a delta. To increase the vertical component radiation, the antenna can be powered from the side. The input impedance of the dual element antenna is close to 60 ohms, and both 50 ohm and 75 ohm coaxial cables are suitable for operation. The gain of a two-element VHF loop antenna is at least 5 dB (above the dipole) and the ratio of radiation in the forward and reverse direction can reach 20 dB. When working with this antenna, it is useful to use a balun.

Circularly polarized loop antenna

An interesting design for a circularly polarized loop antenna has been proposed in the literature. Circularly polarized antennas are used for communication via satellites. Dual power loop antenna with 90 phase shift° allows you to synthesize a radio wave that has circular polarization. The loop antenna power circuit is shown in Fig. 33. When designing an antenna, it is necessary to take into account that the length L can be any reasonable, and the λ / 4 length should correspond to the wavelength in the cable.

Figure 33 Circularly polarized loop antenna

To increase the gain, this antenna can be used in conjunction with a loop reflector and a director. The frame must be powered only through a balun. The simplest balun is shown in Fig. 34.

Figure 34 The simplest balun

Industrial antennas of the range of 145 MHz

Currently, you can find a large selection of branded antennas for the 145 MHz range on sale. If you have the money, of course, you can buy any of these antennas. It should be noted that it is advisable to purchase solid antennas already tuned to the 145 MHz range. The antenna must have a protective coating that protects it from corrosion by acid rain, which can fall in a modern city. Telescopic antennas are unreliable in urban environments and may fail over time.

When assembling antennas, it is necessary to strictly follow all instructions in the assembly instructions, and do not spare silicone grease for waterproofing connectors, telescopic joints and screw connections in matching devices.

Literature

1.I. Grigorov (RK 3 ZK ). Matching devices of the 144 MHz range // Radio amateur. HF and VHF.
-1997.-№ 12.- p. 29.

2.Barry Bootle. (W9YCW) Hairpin Match for the Collinear - Coaxial Arrau // QST.-1984.-October.-P.39.

3.Doug DeMaw (W1FB) Build Your Own 5/8-Wave Antenna for 146 MHz // QST.-1979.-June.-P.15-16.

4. S. Bunin. Antenna for communication via satellite // Radio.- 1985.- No. 12.- p. twenty.

5.D.S.Robertson, VK5RN The “Quadraquad” - Circular Polarization the Easy Way //QST.-April.-1984.
-pages16-18.