Classic option. Both sections of the antenna are mounted vertically. Mainly used on HF.
This vertical antenna is well known to VHF enthusiasts as the J-antenna. The figure shows the general diagram of the antenna - the classic version. It consists of two sections: emitting L/2 and matching L/4. The high impedance of a half-wave emitter can be matched (reduced) to a low impedance using a quarter-wave, end-closed line. This method has long been known and is widely used in practice.
On the quarter-wave line, you can find two points XX with an impedance of 500m (or 750m) to connect the corresponding coaxial cable (feeder). When connecting the cable, it is advisable to provide a balun choke or transformer. The quarter-wave line itself is easiest to make from 450-ohm ribbon cable.
DK7ZB has manufactured and tested several similar antennas for the amateur bands of 2, 6, 12 and 30 meters. I compiled the data for the remaining ranges into a table, which is very convenient to use when experimenting. Below he provides mathematical calculations for independent calculations, based on specific calculation conditions:
Emitter: L/2 = 0.471 X (m) - 2mm insulated copper wire;
Quarter wave line: L/4 = 0.223X (M) - 450 ohm ribbon cable (Wireman);
Points XX are located approximately 5...10% from the closed end of the quarter-wave line.
When installing an antenna, in addition to the basic vertical location, the following options can be considered:
Design dimensions:
Range L/2 L/4 XX MHz SWR Bandwidth (kHz) (m) (m) (m) (cm) (SWR
Calculated values marked (*) require re-checking.
Quarter-wave (X/4) line lengths are based on WireMan 450 Ohm RF ribbon cable.
The values given in the table are valid when the antenna is installed freely in space. If the radiating wire is fixed to any supporting insulated elements, then its length should be reduced by approximately 2...3%, because the operating frequency in this case is reduced
Just a short time ago, mostly home-made equipment was used to operate in the 144-145 MHz range. 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 radio stations of the Palma type to the amateur VHF 145 MHz band, obtaining a radio station operating on several channels. Then “Viols”, and later “Mayaks”, operating on forty channels, became available to radio amateurs. These radio stations then looked simply fantastic in their capabilities!
Currently, you can relatively inexpensively purchase multi-channel portable VHF transceivers from world-famous companies - “YAESU”, “KENWOOD”, “ALINCO”, which in terms of their parameters and ease of operation are significantly superior to both home-made equipment in the 145 MHz range and converted industrial equipment - “Palms” ", "Beacons", "Violas".
But to work through a repeater from home, office, while driving or working from a car, you need an antenna that is more effective than the one used in conjunction with a portable “rubber band” 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 145 MHz antenna is not cheap.
This material is dedicated to the production 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, thick wire is usually used - with a diameter of 1 to 10 mm (sometimes thicker vibrators are used, especially in commercial antennas), antennas in the 145 MHz range are broadband. This often allows, when making an antenna exactly to the specified dimensions, to do without it. additional settings on the 145 MHz band.
To tune antennas in the 145 MHz range, you must have an 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 manufacturing of the bridge meter and, therefore, its correct operation on this range, it is possible to accurately determine the input impedance of VHF antennas. But even using only a pass-through SWR 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” mode and domestic portable VHF radio stations such as “Dnepr”, “Viola”, “VEBR”, is quite enough to operate many types of SWR meters. The “LOW” mode allows you to tune antennas without fear of failure of the output stage of the radio station at any input impedance of the antenna.
Before you start 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 designed to operate in 50 and 75 Ohm transmission paths. When setting up VHF antennas, it is advisable 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 an antenna, the level of field strength created by the tuned antenna is measured relative to the control one. This makes it possible to judge the comparative efficiency of the tuned antenna. Of course, if you use a standard calibrated field strength meter for measurements, you can get an accurate estimate of the antenna's performance. When using a calibrated field meter, it is easy to measure the antenna radiation pattern. But even using homemade field strength meters during measurements and having obtained only a qualitative picture of the distribution of electromagnetic field strength, one can fully draw a conclusion about the efficiency of the tuned antenna and approximately estimate its radiation pattern. Let's consider practical designs of VHF antennas.
Simple antennas
The simplest outdoor VHF antenna (Fig. 1) can be made using an antenna operating 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 block, 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 is of the minimum required length. 4 counterweights, each 50 cm long, are attached to the edges of the corner. It is necessary to ensure good electrical contact between the counterweights and the antenna connector with the metal corner. The radio's shortened twisted antenna has an input impedance of 30-40 ohms, so a coaxial cable with a characteristic impedance of 50 ohms can be used to power it. Using the angle of inclination of the counterweights, you can change the input impedance of the antenna within certain limits, and, therefore, match the antenna with the coaxial cable. Instead of the branded “elastic band,” you can temporarily use an antenna made of copper wire with a diameter of 1-2 mm and a length of 48 cm, which is inserted into the antenna socket with its sharpened end.
Figure 1. Simple outdoor VHF antenna
Figure 2. Design of a simple outdoor VHF antenna
A VHF antenna made of coaxial cable with the outer braid removed works reliably. The cable is embedded in an RF connector similar to the connector of a “proprietary” antenna (Fig. 3). The length of the coaxial cable used to make the antenna is 48 cm. This antenna can be used in conjunction with a portable radio station to replace a broken or lost standard antenna.
Figure 3. Simple homemade VHF antenna
To quickly manufacture an external VHF antenna, you can use a connecting coaxial cable 2-3 meters long, which is terminated with connectors corresponding to the antenna socket 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 counterweights 50 cm long are screwed on from the other end of the tee, or another type of radio ground for the VHF antenna is connected through the connector.
Figure 4. Simple remote VHF antenna
Homemade antennas portable radio
If the standard antenna of a portable radio station is lost or broken, you can make a homemade twisted VHF antenna. To do this, use a base - 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 copper wire with a diameter of 1-1.5 mm is wound. To tune a twisted antenna, it is very convenient to use a frequency response meter, 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, pushing apart the turns of the antenna, the twisted antenna is tuned to resonance at 145 MHz.
This procedure is not very complicated, and by setting up 2-3 twisted antennas, a radio amateur can configure new twisted antennas in literally 5-10 minutes, of course, if the above-mentioned devices are available. After setting up the antenna, it is necessary to fix the turns either with electrical tape, or with a cambric soaked in acetone, or with a heat-shrinkable tube. After fixing the turns, it is necessary to once again check the frequency of the antenna 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 operate effectively, multiple quarter-wave counterweights must be used. This complicates the design for a quarter-wave field antenna, which must be located in space relative to the VHF transceiver. In this case, you can use a VHF antenna with an electrical length of L/2, which does not require counterweights for its operation, and provides a directivity pattern pressed to the ground and ease of installation. For an antenna with an electrical length of L/2, the problem is to match its high input impedance with the low characteristic impedance of the coaxial cable. An antenna with a length of L/2 and a diameter of 1 mm will have an input impedance on the 145 MHz band 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 selecting the connection points of the coaxial cable to the resonator for its effective operation and fine-tuning the antenna pin to resonance. The resonator dimensions for the 145 MHz range are also relatively large. Destabilizing factors on the antenna when it is matched using a resonator will be especially pronounced.
However, with low powers supplied to the antenna, quite satisfactory matching can be achieved using a P-circuit, similar to what is described in the literature. The diagram of a half-wave antenna and its matching device is shown in Fig. 5. The length of the antenna pin is selected slightly shorter or longer than the L/2 length. This is necessary because even with a slight difference in the electrical length of the antenna from L/2, the active resistance of the antenna impedance decreases noticeably, and its reactive part at the initial stage increases slightly. As a result, it is possible to match such a shortened antenna using the P-circuit with greater efficiency than matching an antenna with a length of exactly L/2. It is preferable to use an antenna with a length slightly longer than L/2.
Figure 5. VHF antenna matching using a P-circuit
The matching device used air tuning capacitors of the KPVM-1 type. Coil L1 contains 5 turns of 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.
Setting up the antenna is not difficult. By including an SWR meter in the antenna cable path and at the same time measuring the level of field strength created by the antenna by changing the capacitance of variable capacitors C1 and C2, compressing and stretching the turns of coil L1, we achieve the minimum readings of the SWR meter and, accordingly, the maximum readings of the field strength meter. If these two maximums do not coincide, you need to slightly change the length of the antenna and repeat its adjustment again.
The matching device was placed in a housing soldered from foil 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 field conditions the antenna can be suspended from the upper end on a tree using a fishing line, as shown in Fig. 6. A 50 ohm coaxial cable can be used to power the antenna. Using a 75-ohm coaxial cable will slightly increase the efficiency of the antenna matching device, but at the same time will require configuring the radio output stage to operate at a 75-ohm load.
Figure 6. Antenna installation for field use
Foil based window antennas
Based on adhesive foil used in systems burglar alarm can be built very simple designs window VHF antennas. This foil can be purchased with an adhesive base. Then, having freed one side of the foil from the protective layer, you simply press it against the glass and the foil instantly sticks securely. Foil without an adhesive base can be glued to the glass using varnish or Moment type glue. But for this you need to have some skill. The foil can even be secured to the window using adhesive tape.
With appropriate training, it is quite possible to make a high-quality soldered connection between the central core and braid of a coaxial cable with aluminum foil. Based on personal experience, each type of such foil requires its own flux for soldering. Some types of foil can be soldered well even using only rosin, some can be soldered using soldering oil, other types of foil require the use of active fluxes. The flux must be tested on the specific type of foil used to make the antenna in advance of installation.
Good results are obtained by using a foil fiberglass substrate for soldering and attaching the foil, as shown in Fig. 7. A piece of foil fiberglass laminate is glued to the glass using Moment glue, the antenna foil is soldered to the edges of the foil, the cores of the coaxial cable are soldered to the copper foil of the fiberglass laminate at a short distance from the foil. After soldering, the connection must be protected with moisture-resistant varnish or glue. Otherwise, corrosion of this connection may occur.
Figure 7. Connecting the antenna foil to the coaxial cable
Let's analyze the practical designs of window antennas built on the basis of foil.
Vertical window dipole antenna
The diagram of a vertical dipole window VHF antenna based on foil is shown in Fig. 8.
Figure 8. Windowed vertical dipole VHF antenna
The quarter-wave pole and counterweight are positioned at an angle of 135 degrees to keep the antenna system's input impedance close to 50 ohms. This makes it possible to use a coaxial cable with a wave impedance of 50 Ohms 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 along the glass for as long as possible.
Foil Based Window Loop Antenna
The frame window VHF antenna shown in Fig. will work more efficiently than a dipole vertical antenna. 9. When feeding the antenna from a side angle, the maximum radiated polarization is located in the vertical plane; when feeding the antenna in the bottom angle, the maximum radiated polarization is in the horizontal plane. But at any position of the feed points, the antenna emits a radio wave with combined polarization, both 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 while moving.
Figure 9. Frame window VHF antenna
The input impedance of the window loop antenna is 110 ohms. To match this resistance with a coaxial cable with a characteristic impedance of 50 Ohms, a quarter-wave section of coaxial cable with a characteristic impedance of 75 Ohms is used. The cable should run perpendicular to the antenna axis for as long as possible. Loop antenna has a gain approximately 2 dB higher relative to a dipole window antenna.
When made from foil window antennas with a width of 6-20 mm, they do not require tuning and operate in a frequency range much wider than the amateur band of 145 MHz. If the resulting resonant frequency of the antennas turns out to be lower than the required one, then the dipole can be adjusted by symmetrically cutting off the foil from its ends. The loop antenna can be configured using a jumper made from the same foil that was used to make the antenna. The foil closes the antenna sheet in the corner, opposite the power points. Once configured, contact between the jumper and the antenna can be achieved either by soldering or using adhesive tape. Such adhesive tape should press the jumper firmly enough to the antenna surface in order to ensure reliable electrical contact with it.
Significant power levels can be supplied to antennas made of foil - up to 100 watts or more.
Outdoor vertical antenna
When placing an antenna outside a room, the question always arises of protecting the opening of the coaxial cable from atmospheric influences, using a high-quality antenna support insulator, moisture-resistant wire for antennas, etc. These problems can be solved by making 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 a coaxial cable can fit tightly. Then the cable is threaded there, protruded from the pipe, exposed at a distance of 48 cm, the cable screen is twisted and soldered at a length of 48 cm. The cable with the antenna is inserted back into the pipe. Standard plugs are placed on the top and bottom of the pipe. Moisture-proofing the hole where the coaxial cable enters is not difficult. This can be done using automotive silicone sealant or fast-curing automotive epoxy. The result is a beautiful, moisture-proof, protected antenna that can operate under the influence of weather conditions for many years.
To fix the vibrator and antenna counterweight inside, you can use 1-2 cardboard or plastic washers, tightly placed on the antenna vibrators. The pipe with the antenna can be installed on a window frame, on a non-metallic mast, or placed in another convenient place.
Simple coaxial collinear antenna
A simple collinear coaxial VHF antenna can be made from coaxial cable. To protect this antenna from atmospheric influences, a piece of water pipe can be used, 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 greater than a quarter-wave vertical. It does not require counterweights for its operation (although their presence improves the performance of the antenna) and provides a directivity pattern close to the horizon. A description of such an antenna has repeatedly appeared on the pages of domestic and foreign amateur radio literature, but the most successful description was presented in the literature.
Antenna dimensions in Fig. 11 are indicated in centimeters for a coaxial cable with a shortening factor of 0.66. Most coaxial cables with polyethylene insulation have this shortening factor. The dimensions of the matching loop are shown in Fig. 12. Without the use of this loop, the SWR of the antenna system may exceed 1.7. If the antenna is tuned below the 145 MHz range, it is necessary to shorten the upper section slightly, if higher, then lengthen it. Of course, optimal tuning is possible by proportionally shortening and lengthening all parts of the antenna, but this is difficult to do in amateur radio conditions.
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 advisable. The antenna can be moved away from the building using wooden slats, as shown in Fig. 13. The antenna can withstand significant power supplied to it, up to 100 watts or more, and can be used in conjunction with both stationary and portable VHF radio stations. Using such an antenna in conjunction with low-power portable radio stations will give the greatest effect.
Figure 13. Collinear Antenna Installation
Simple collinear antenna
This antenna was assembled by me similar to the design of a car remote antenna used in a cellular radiotelephone. To convert it to the 145 MHz amateur band, I proportionally changed all the dimensions of the “telephone” antenna. The result was an antenna, 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 pin. A coaxial cable with a characteristic impedance of 50 Ohms was used to power the antenna.
Figure 14. Simple collinear antenna
Practical design antenna is shown in Fig. 15. The antenna was made of a whole piece of copper wire with a diameter of 1 mm. Coil L1 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 the design is made exactly to size, the antenna requires virtually no adjustment. It may be necessary to slightly adjust the antenna by compressing and stretching the coil turns to achieve a minimum SWR. The antenna was placed in a plastic water pipe. Inside the pipe, the antenna wire was fixed using pieces of foam plastic. Four quarter-wave counterweights were installed at the lower end of the pipe. They were threaded and secured to a plastic pipe using nuts. Counterweights can be 2-4 mm in diameter, depending on the ability to thread them. For their manufacture, you can use copper, brass, or bronze wire.
Figure 15. Design of a simple collinear antenna
The antenna can be installed on wooden slats on the balcony (as shown in Fig. 13). This antenna can withstand significant levels of power applied to it.
This antenna can be considered as a shortened HF antenna with a central extension coil. Indeed, the antenna resonance measured using a bridge resistance meter in the HF range turned out to lie in the frequency region of 27.5 MHz. Obviously, by varying the diameter of the coil and its length, but maintaining the length of the winding wire, you can ensure that the antenna operates both in the VHF range of 145 MHz and in one of the HF bands - 12 or 10 meters. To operate on the HF bands, it is necessary to connect four counterweights with a length of L/4 for the selected HF band to the antenna. This dual use of the antenna will make it even more versatile.
Experimental 5/8 wave antenna
When conducting experiments with radio stations in 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 receiving path or to adjust the transmitter output stage. For these purposes 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. A thread is cut at the end of the wire connected to the coil, 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 Ohms by connecting to different turns of the coil, and the tuning section can be slightly shortened. The antenna diagram is shown in Fig. 16. The antenna design is shown in Fig. 17.
Figure 16. Diagram of a simple 5/8 wave VHF antenna
Figure 17. Design 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 there is a thread into which the antenna vibrator is screwed on one side, and on the other side it is screwed to a piece of foil fiberglass measuring 20*30 cm, which serves as the “ground” of the antenna. A magnet from an old speaker was glued to the back of it, as a result of which the antenna can be attached to a windowsill, to a heating radiator, or to other iron objects.
The coil contains 10.5 turns of wire with a diameter of 1 mm. The coil wire is evenly distributed throughout the frame. The outlet to the coaxial cable is made 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 SWR in the cable no worse than 1:1.3. Tuning the antenna is carried out by shortening its upper part with wire cutters, which is initially made slightly longer than necessary.
I conducted experiments on installing this antenna on window glass. In this case, a vibrator initially 125 centimeters long made of aluminum foil was glued to the center of the window. The same extension coil was used and was installed on the window frame. The counterweights were made of foil. The ends of the antenna and counterweights were bent slightly to fit on the window glass. A view of a 5/8 window - wave VHF antenna is shown in Fig. 18. The antenna is easily tuned to resonance by gradually shortening the vibrator foil using a blade, and gradually switching the coil turns to a minimum 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 cases where communication using a standard rubber band is not possible, a half-wave antenna can be used. It does not require “ground” for its operation and when working over long distances it provides a gain of up to 10 dB compared to a standard “rubber band”. These are quite realistic figures, considering that the physical length of a half-wave antenna is almost 10 times longer than the rubber band.
The half-wave antenna is powered by voltage and has a high input impedance that can reach 1000 Ohms. Therefore, this antenna requires a matching device when used in conjunction with a radio station having a 50 ohm output. One of the options for a matching device based on a P-circuit has already been described in this chapter. Therefore, for variety, for this antenna we will consider using another matching device made on a parallel circuit. In terms of their operating efficiency, these matching devices are approximately equal. The diagram of a half-wave VHF antenna together with a matching device on a parallel circuit is shown in Fig. 19.
Figure 19. Half-wave VHF antenna with matching device
The circuit coil contains 5 turns of silver-plated copper wire with a diameter of 0.8 mm, wound on a mandrel with a diameter of 7 mm along a length of 8 mm. Setting up the matching device consists of tuning the circuit L1C1 into resonance using the variable capacitor C1, and using the variable capacitor C2 to regulate the connection of the circuit with the output of the transmitter. Initially, the capacitor is connected to the third turn of the coil from its grounded end. Variable capacitors C1 and C2 must be with an air dielectric.
For the antenna vibrator, it is advisable to use a telescopic antenna. This will make it possible to carry the half-wave antenna in a compact folded state. This also makes it easier to configure the antenna together with a real transceiver. At initial setup antenna, its length is 100 cm. During the setup process, this length can be slightly adjusted according to better work antennas. It is advisable to make appropriate marks on the antenna so that you can subsequently install the antenna directly to the resonant length from its folded position. The box where the matching device is located must be made of plastic in order to reduce the capacitance of the coil to “ground”; it can be made of foil fiberglass. This depends on the actual operating conditions of the antenna.
The antenna is tuned using the field strength indicator. Using an SWR meter, tuning an antenna is advisable only if it is not operated on the radio body, but when an extension coaxial cable is used in conjunction with it.
When operating the antenna twice on the radio body and using an extension coaxial cable, two marks are made on the antenna pin, one corresponding to the maximum field strength level when operating the antenna on the radio body, and the other mark corresponds to the minimum SWR when using an extension coaxial cable with the antenna. Usually these two marks are slightly different.
Vertical continuous antennas with gamma matching
Vertical antennas made from a single vibrator are wind-resistant, easy to install, and take up little space. To perform them, you can use copper tubes, aluminum power electrical wire with a diameter of 6-20 mm. These antennas can be quite easily matched with a coaxial cable with a characteristic impedance of both 50 and 75 Ohms.
Very simple to implement and easy to configure is a continuous half-wave VHF antenna, the design of which is shown in Fig. 20. Gamma matching is used to power it through a coaxial cable. The material from which the antenna vibrator and gamma matching are made must be the same, for example, copper or aluminum. Due to the mutual electrochemical corrosion of many pairs of materials, it is unacceptable to use different metals to perform the 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 gamma matching of the antenna using a shorting jumper as shown in Fig. 21. In this case, the surface of the pin and the gamma matching conductor is carefully cleaned and using a bare wire clamp as shown in Fig. 21a achieve a minimum SWR in the coaxial antenna power cable. Then, at this point, the gamma matching wire is slightly flattened, drilled and connected with a screw to the antenna surface, as shown in Fig. 21b. It is also possible to use soldering.
Figure 21. Setting up gamma matching of a copper antenna
If an aluminum wire from a power electrical cable in plastic insulation is used for the antenna, then it is advisable to leave this insulation to prevent corrosion of the aluminum wire by acid rain, which is inevitable in urban environments. In this case, the gamma matching of the antenna 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 an SWR in the cable of less than 1.5, then the gamma matching length must be reduced and the adjustment must be repeated again.
Figure 22. Setting up gamma matching of an aluminum-copper antenna
If you have enough space and materials, you can install a continuous vertical wave VHF antenna. The wave antenna works more efficiently than the half-wave antenna shown in Fig. 20. A wave antenna provides a radiation pattern more close to the horizon than a half-wave antenna. The wave antenna can be matched 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 making these antennas, it is desirable that the coaxial power cable be perpendicular to the antenna at least 2 meters. Using a balun in conjunction with a continuous antenna will increase its efficiency. When using a balun, it is necessary to use symmetrical gamma matching. The connection of the balun is shown in Fig. 24.
Figure 24. Connecting a balun to a continuous antenna
Any other known balancing device can also be used as an antenna balun. When placing the antenna near conductive objects, you may have to slightly reduce the length of the antenna due to the influence of these objects on it.
Round VHF antenna
If placement in space vertical antennas, shown in Fig. 20 and fig. 23 in their traditional vertical position is difficult, they can be placed by folding the antenna sheet into a circle. The position of the half-wave antenna shown in Fig. 20 in a “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 radio stations. Although, theoretically, the level of vertical polarization will be higher with the side feeding of round VHF antennas, in practice this difference is not very noticeable, and the side feeding of the antenna complicates its installation. The side feeding of the circular antenna is shown in Fig. 27.
Figure 25. Continuous round vertical half-wave VHF antenna
Figure 26. Continuous round vertical wave VHF antenna
Figure 27. Side feeding of round VHF antennas
A round VHF antenna can be placed indoors, for example, between window frames, or outdoors, on a balcony or on the roof. When placing a circular antenna in a horizontal plane, we obtain a circular radiation pattern in the horizontal plane and the operation of the antenna with horizontal polarization. This may be necessary in some cases when conducting amateur radio communications.
Passive "amplifier" of a portable station
When testing portable radios or working with them, sometimes there is not enough “just a little” power for reliable communication. I made a passive “amplifier” for portable VHF stations. A passive "amplifier" can add up to 2-3 dB to a radio station's on-air signal. This is often enough to reliably open the squelch of the correspondent station and ensure reliable operation. The design of a passive “amplifier” is shown in Fig. 28.
Figure 28. Passive “amplifier”
The passive “amplifier” is a fairly large tinned coffee can (the bigger the better). A connector similar to the antenna connector of a radio station is inserted into the bottom of the can, and a connector for connecting to the antenna socket is sealed into the lid of the can. 4 counterweights 48 cm long are soldered to the can. When working with a radio station, this “amplifier” is switched on between the standard antenna and the radio station. Due to the more efficient “ground”, the strength of the emitted signal increases at the receiving site. Other antennas can be used in conjunction with this “amplifier”, for example, an L/4 pin made of copper wire, simply inserted into the antenna socket.
Wideband survey antenna
Many imported portable radio stations provide reception not only in the amateur range of 145 MHz, but also in the survey ranges of 130-150 MHz or 140-160 MHz. In this case, for successful reception in the surveillance bands, where a twisted antenna tuned to 145 MHz does not work effectively, you can use a wideband VHF antenna. The antenna diagram is shown in Fig. 29 and the dimensions for different operating ranges are given in table. 1.
Figure 29. Wideband VHF vibrator
| Range, MHz | 130-150 | 140-160 |
| Size A, cm | 26 | 24 |
| Size B, cm | 54 | 47 |
Table 1. Wideband VHF antenna dimensions
To operate the antenna, you can use a coaxial cable with a characteristic impedance of 50 Ohms. The antenna sheet can be made of foil and glued to the window. You can make the antenna sheet from an aluminum sheet, or by printing it on a piece of foil fiberglass of suitable sizes. This antenna can receive and transmit in the specified frequency ranges with high efficiency.
Zigzag antenna
Some long-distance service VHF 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, which 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 radiation pattern pressed to the horizon. The type of polarization emitted by the antenna is combined - vertical and horizontal. To operate the antenna, it is advisable to use a balun.
In antennas used in service communication stations, a reflector made of a metal mesh is usually placed behind the elementary zigzag antennas. The reflector ensures one-way directivity of the antenna. Depending on the number of vibrators included in the antenna and the number of zigzag antennas connected together, you can obtain the required antenna gain.
Radio amateurs practically do not use such antennas, although they are easy to make for the amateur VHF bands of 145 and 430 MHz. To make the antenna sheet, you can use 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 the fabric of which a rigid coaxial cable was used, was given in the literature.
Kharchenko antenna in the 145 MHz range
The Kharchenko antenna is widely used in Russia for television reception and in official radio communications. But radio amateurs use it to operate on the 145 MHz band. This antenna is one of the few that works very efficiently and requires virtually no adjustment. The Kharchenko antenna diagram is shown in Fig. 31.
Figure 31. Kharchenko antenna
To operate the antenna, you can use either 50 or 75 Ohm coaxial cable. The antenna is broadband, operating in a frequency band of at least 10 MHz on the 145 MHz band. To create a one-way radiation pattern, a metal mesh is used behind the antenna, located at a distance of (0.17-0.22)L.
The Kharchenko antenna provides a lobe width of the radiation pattern in the vertical and horizontal planes close to 60 degrees. To further narrow the radiation pattern, passive elements are used in the form of vibrators 0.45L long, located at a distance of 0.2L from the diagonal of the frame square. To create a narrow radiation pattern and increase the gain of the antenna system, several combined antennas are used.
145 MHz loop directional antennas
One of the most popular directional antennas for operating in the 145 MHz band are loop antennas. The most common in the 145 MHz band are two-element loop antennas. In this case, the 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
Antenna elements can be made not only in the form of a square but also in the form of a circle or delta. To increase the radiation of the vertical component, the antenna can be fed from the side. The input impedance of a two-element antenna is close to 60 ohms, and both 50-ohm and 75-ohm coaxial cable 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 directions can reach 20 dB. When working with this antenna, it is useful to use a balun.
Circular polarized loop antenna
An interesting circularly polarized loop antenna design has been proposed in the literature. Antennas with circular polarization are used for communication through satellites. Double feeding of the loop antenna with a phase shift of 90 degrees allows you to synthesize a radio wave that has circular polarization. The loop antenna power supply circuit is shown in Fig. 33. When designing an antenna, it must be taken into account that the length L can be any reasonable, and the length L/4 must 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 frame reflector and director. The frame must be powered only through a balun. The simplest balancing device is shown in Fig. 34.
Figure 34. The simplest balancing device
Industrial antennas in the 145 MHz range
Currently on sale you can find big choice proprietary antennas for the 145 MHz range. If you have money, of course, you can buy any of these antennas. Please note that it is advisable to purchase solid antennas already tuned to the 145 MHz range. The antenna must have a protective coating to protect it from corrosion by acid rain, which can fall in a modern city. Telescopic antennas are unreliable in city operating conditions and may fail over time.
When assembling antennas, you must strictly follow all instructions in the assembly instructions, and do not skimp on silicone grease for waterproofing connectors, telescopic connections and screw connections in matching devices.
Literature
- I. Grigorov (RK3ZK). Matching devices of the 144 MHz range//Radio Amateur. HF and VHF.-1997.-No. 12.-P.29.
- Barry Bootle. (W9YCW) Hairpin Match for the Collinear – Coaxial Arrau//QST.-1984.-October.-P.39.
- Doug DeMaw (W1FB) Build Your Own 5/8-Wave Antenna for 146 MHz//QST.-1979.-June.-P.15-16.
- S. Bunin. Antenna for communication through satellites // Radio.- 1985.- No. 12.-S. 20.
- D.S.Robertson ,VK5RN The “Quadraquad” – Circular Polarization the Easy Way //QST.-April.-1984.-pages16-18.
To carry out local communications on VHF (including through repeaters), you need an antenna with a circular radiation pattern and noticeable gain. In amateur radio practice, this problem is usually solved by using elongated vertical antennas, consisting of several emitters, which are powered through phasing two-wire lines. Very similar antenna models are produced by many foreign companies, and almost identical models are sometimes produced under different names. Typical antenna of this class (for example, model ARX-2B from CUSHCRAFT) has a gain of 7 dB and SWR at the resonant frequency of no more than 1.2 (typical value). Bandwidth is about 3 MHz. In the horizontal plane, the antenna has a circular radiation pattern; in the vertical plane, the maximum radiation angle is 7 degrees. Typically, antennas have a certain margin for adjustments, so during installation their operating frequency can be varied within wide limits (for example, for the model mentioned above - in the band from 135 to 160 MHz). Similar antennas can be made in amateur conditions.
The design of this type of antenna is shown in Fig. 1. It is made of thin-walled aluminum tubes and is installed through an insulator on a grounded metal mast (the total height of the antenna is 4.3 m). Antenna dimensions are for the 2 meter amateur band, with a center frequency of 145 MHz.
Element 1 is a tube with a length of 890 and a diameter of 9 mm. A plug is installed in the upper part of element 1 to prevent moisture from entering the antenna. Element 3 - tube 700 long, 13 mm in diameter. Element 6 is a tube with a length of 530 and a diameter of 13 mm. Element 7 is a tube with a length of 380 and a diameter of 16 mm. Element 8 is a tube with a length of 1000 and a diameter of 19 mm.
At the upper ends of tubes 3, 7, 8, vertical cuts 30 mm long are made, ensuring a tighter fit of the internal fixed elements. Fixation of the tubular elements is carried out using expansion clamps 2, a sketch of which is shown in Fig. 2. The design uses three clamps with internal diameters D=13, 16 and 19 mm.
Elements 3 and 6 are electrically connected to each other through phasing element 5. For this purpose, an insulator is installed between elements 3 and 6, Fig. 3. The phasing element is a U-shaped bracket made of aluminum wire with a diameter of 6 mm. At the ends of tubes 3 and 6, inserted into the insulator at a distance of 10 mm from the edge, holes with a diameter of 6 mm are drilled. Using M5 screws, elements 3, 5 and 6 are fastened together through threaded holes in the insulator. The length of the phasing element 5 is set according to the dimensions shown in Fig. 1.
The antenna is installed through insulator 11 (Fig. 4) on a metal mast 17 with a diameter of 32 mm. At the upper end of the mast, a metal cup 16 with an internal diameter of 32 mm is fixed (by welding or any other mechanical connection). An insulator 11 is placed in this glass. The depth of the glass 16 is chosen so that the insulator 11 protrudes from it by 30 mm.
Metal corners 13 are attached to elements 8 and 16, as can be seen in Fig. 1, using screws. At the ends of the corners remote from the antenna, one hole with a diameter of 127 mm is drilled from a copper wire with a diameter of 5 mm.
On the corner attached to part 16, closer to the antenna, a 50-ohm connector socket is installed so that its threaded or bayonet part faces down towards the base of the antenna. A piece of copper wire 12 with a diameter of 5 and a length of 130 mm is soldered to the central terminal of the connector (Fig. 5). At one end the wire is flattened and a hole is drilled in it equal to the diameter of the central pin of the connector. The wire is bent in such a way that, without touching the antenna, its opposite end rests on element 9. Using a metal bracket (part 10, Fig. 6) and an M5 screw located on the bracket, the end of wire 12 is fixed on element 9. B At the same time, this contact is movable and is used when tuning the antenna. By moving bracket 10 within certain limits around the circumference of ring 9, select its position at which the SWR of the antenna is minimal.
Before installing it, put a metal ring 18 on the antenna mast, made according to Fig. 7. Three aluminum counterweights 19 with a length of 521 and a diameter of 6 mm are screwed into this ring. At one end of the counterweights there is an M6 thread 20 mm long. Before installing the counterweights in place, lock nuts are screwed onto the threads.
Angle 13 is attached to part 18 with a screw in the same way as part 16. Only the connector here is installed as a pass-through connector. A cable with connectors at the ends and a total length of 1272 mm is manufactured separately.
Ring 18 is installed along the length of the stretched attached cable and, screwing in the counterweights all the way, it is rigidly fixed to the antenna mast. After this, tighten the locknuts.
The tube lengths given in this article correspond to the antenna version, which allows you to adjust its operating frequency within a wide range. For an antenna for a range of 2 meters, the emitters can be non-composite, which will significantly simplify the design of the antenna.
| http://www.chipinfo.ru/literature/radio/199905/p60_61.html |
A. Kalashnik
Radiohobby 1/2001
VHF antennas
In recent years, the interest of radio amateurs in the 2-meter range has been constantly growing due to the increase in the number of FM repeaters and, accordingly, improving conditions for development mobile communications, networks of various BBS and portals, incl. with Internet access, as well as satellite repeaters. The increase in activity is also facilitated by permission from March 1, 1998 for beginning radio amateurs to work on VHF.
When operating on the 2-meter band, antennas with both vertical polarization (mainly for mobile communications and when working through repeaters) and horizontal polarization are used. In this case, it is desirable to have an antenna with a circular radiation pattern in both horizontal and vertical planes. The latter is very important when working through satellite (satellite) repeaters. For these purposes, as a rule, several antennas are used, which reduces the efficiency of operation under the condition of long-distance unstable transmission on the 2-meter range.
The author managed to solve this problem by implementing an antenna with an almost spherical radiation pattern. In this case, the antenna can radiate and, accordingly, receive electromagnetic waves with both vertical and horizontal polarization.
The basis of the design is the popular J-antenna (Fig. 1). It is a vertical dipole fed from the lower end using a short-circuited quarter-wave line. As is known, this antenna works only with vertical polarization and has a circular pattern in the horizontal plane with a deep minimum in the vertical direction.
The author proposed changing the shape of the vertical emitter of this antenna by bending the dipole in half at 90°. In this case, the horizontal part of the dipole in the first version consisted of two opposite elements of length L/l each (Fig. 2) and was first described in the collection "Infoix" No. 4/1990, pp. 42,43.
In the latest modification, the author proposed making the horizontal part of the emitter from 4 mutually perpendicular segments of length l/4, which have electrical contact with the vertical part of the emitter (Fig. 3). The antenna design is simple to manufacture and easily repeatable even for novice radio amateurs. The vertical parts of the antenna are made of pipe with a diameter of 32 mm. Material - bronze, brass, copper, as well as aluminum alloys, provided that reliable electrical contact is ensured in all parts of the antenna and matching device (soldering or welding). The horizontal cross-shaped part is made of a rod or tube with a diameter of 6 mm (the material is similar to the used pipe with a diameter of 32 mm).
This design retains the advantage of the J-antenna in that the lower end of the short-circuited quarter-wave line can be grounded, for example electrically connected to a grounded mast, in which case the entire antenna can serve as a good lightning rod. The setup consists of selecting the location for connecting the power cable to the matching line (Fig. 4) according to the minimum SWR. The author used RK-75. but you can also use a feeder with a characteristic impedance of 50 Ohms. With the dimensions indicated in Fig. 3, 4 and a 75-ohm feeder, SWR = 1.0 near 145.5 MHz.
The antenna is mounted on a metal grounded mast, at a height of 7 m above the ground, but a mast of any material and design can be used. Foreign conductive objects must be removed from horizontal elements more than 2 meters. With appropriate changes in geometric dimensions, such an antenna can be built for other VHF bands.
This antenna has been in use by the author since 1983. It showed good results for all types of transmission, as well as for communications through amateur satellites in their visibility zone and without signal failure “overhead”. During Field Day 2000, an experiment was carried out on the UT0H base, during which the signals of my beacon, which used the described antenna, were received by antennas with both vertical and horizontal polarization with approximately the same volume.
From the editor. Figures 1 and 4 show two options for connecting the cable to the matching line. In the first case (Fig. 1), the central core is soldered to the line conductor connected to the emitter, and in the author's version (Fig. 4) - vice versa. Both options are equivalent, although in the publication the cable connection method shown in Fig. 1 is more common.
Literature
- Benkovsky 3., Lipinsky E. Amateur antennas of short and ultrashort waves: Per. from Polish/Ed. O. P. Frolova. - M.: Radio and communication, 1983. . 480 pp., ill. - (Mass Radio Library; Issue 1052)
To carry out local communications on VHF (including through repeaters), you need an antenna with a circular radiation pattern and noticeable gain. In amateur radio practice, this problem is usually solved by using elongated vertical antennas, consisting of several emitters, which are powered through phasing two-wire lines. Very similar antenna models are produced by many foreign companies, and almost identical models are sometimes produced under different names. A typical antenna of this class (for example, model ARX-2B from CUSHCRAFT) has a gain of 7 dB and an SWR at the resonant frequency of no more than 1.2 (typical value). Bandwidth is about 3 MHz. In the horizontal plane, the antenna has a circular radiation pattern; in the vertical plane, the maximum radiation angle is 7 degrees. Typically, antennas have a certain margin for adjustments, so during installation their operating frequency can be varied within wide limits (for example, for the model mentioned above - in the band from 135 to 160 MHz). Similar antennas can be made in amateur conditions.
The design of this type of antenna is shown in Fig. 1. It is made of thin-walled aluminum tubes and is installed through an insulator on a grounded metal mast (the total height of the antenna is 4.3 m). Antenna dimensions are for the 2 meter amateur band, with a center frequency of 145 MHz.
Element 1 is a tube with a length of 890 and a diameter of 9 mm. A plug is installed in the upper part of element 1 to prevent moisture from entering the antenna. Element 3 - tube 700 long, 13 mm in diameter. Element 6 is a tube with a length of 530 and a diameter of 13 mm. Element 7 is a tube with a length of 380 and a diameter of 16 mm. Element 8 is a tube with a length of 1000 and a diameter of 19 mm.
At the upper ends of tubes 3, 7, 8, vertical cuts 30 mm long are made, ensuring a tighter fit of the internal fixed elements. Fixation of the tubular elements is carried out using expansion clamps 2, a sketch of which is shown in Fig. 2. The design uses three clamps with internal diameters D=13, 16 and 19 mm.
Elements 3 and 6 are electrically connected to each other through phasing element 5. For this purpose, an insulator is installed between elements 3 and 6, Fig. 3. The phasing element is a U-shaped bracket made of aluminum wire with a diameter of 6 mm. At the ends of tubes 3 and 6, inserted into the insulator at a distance of 10 mm from the edge, holes with a diameter of 6 mm are drilled. Using M5 screws, elements 3, 5 and 6 are fastened together through threaded holes in the insulator. The length of the phasing element 5 is set according to the dimensions shown in Fig. 1.
The antenna is installed through insulator 11 (Fig. 4) on a metal mast 17 with a diameter of 32 mm. At the upper end of the mast, a metal cup 16 with an internal diameter of 32 mm is fixed (by welding or any other mechanical connection). An insulator 11 is placed in this glass. The depth of the glass 16 is chosen so that the insulator 11 protrudes from it by 30 mm.
Metal corners 13 are attached to elements 8 and 16, as can be seen in Fig. 1, using screws. At the ends of the corners remote from the antenna, one hole with a diameter of 127 mm is drilled from a copper wire with a diameter of 5 mm.
On the corner attached to part 16, closer to the antenna, a 50-ohm connector socket is installed so that its threaded or bayonet part faces down towards the base of the antenna. A piece of copper wire 12 with a diameter of 5 and a length of 130 mm is soldered to the central terminal of the connector (Fig. 5).
At one end the wire is flattened and a hole is drilled in it equal to the diameter of the central pin of the connector. The wire is bent in such a way that, without touching the antenna, its opposite end rests on element 9. Using a metal bracket (part 10, Fig. 6) and an M5 screw located on the bracket, the end of wire 12 is fixed on element 9. B At the same time, this contact is movable and is used when tuning the antenna. By moving bracket 10 within certain limits around the circumference of ring 9, select its position at which the SWR of the antenna is minimal.
Before installing it, put a metal ring 18 on the antenna mast, made according to Fig. 7. Three aluminum counterweights 19 with a length of 521 and a diameter of 6 mm are screwed into this ring. At one end of the counterweights there is an M6 thread 20 mm long. Before installing the counterweights in place, lock nuts are screwed onto the threads.
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