U-shaped matching devices for HF bands. Simple matching devices. Antenna matching devices. Tuners

Modern transmitting and receiving transistor technology, as a rule, has broadband paths whose input and output resistances are 50 or 75 Ohms. Therefore, to implement the declared parameters of such equipment, it is necessary to provide an active load with a resistance of 50 or 75 Ohms for both the receiving and transmitting parts. I would like to emphasize that the receiving path also requires a matched load!

Of course, in the receiver this cannot be noticed by touch, color or taste without instruments. Apparently, because of this, some shortwave operators “foaming at the mouth” defend the advantages of old RPUs such as R-250, “Mole” and the like over modern technology. Old equipment is most often equipped with an adjustable (or tunable) input circuit, with the help of which you can match the radio control unit with a wire antenna with “SWR = 1 on almost all bands.”

If a radio amateur really wants to check the quality of the matching of the “transceiver input - antenna” circuit, he just needs to assemble a very primitive matching device (MD), for example, a P-circuit consisting of two KPIs with a maximum capacitance of at least 1000 pF (if testing is also planned for low-frequency ranges) and coils with variable inductance. By turning on this control system between the transceiver and the antenna, changing the capacitance of the KPI and the inductance of the coil, the best reception is achieved. If at the same time the values ​​of all elements of the control system tend to zero (to the minimum values), you can safely throw away the control system and, with a clear conscience, work on the air and continue, at least listen to the bands.

For the transmitter path, the lack of optimal load can end more sadly. Sooner or later, the RF power reflected from the mismatched load finds a weak spot in the transceiver path and “burns out” it, or more precisely, any of the elements cannot withstand such an overload. Of course, it is possible to make a silo that is absolutely reliable (for example, by removing no more than 20% of the power from transistors), but then the cost will be comparable to the components of expensive imported equipment.

For example, a 100-watt silo, produced in the USA as a kit for the K2 transceiver, costs 359 USD, and the tuner for it costs 239 USD. And foreign radio amateurs go to such expense in order to get “just some kind of coordination,” which, as the experience of the author of this article shows, many of our users of transistor technology do not think about... Thoughts about matching a transceiver with a load are in the minds of such woe radio amateurs begin to arise only after an accident has occurred in the equipment.

Nothing can be done - these are today's realities. Examinations for obtaining licenses and upgrading amateur radio categories are often carried out formally. At best, the applicant for a license is tested on his knowledge of the telegraph alphabet. Although in modern conditions, in my opinion, it is advisable to place more emphasis on testing technical literacy - there would be fewer “group sex for long-distance work” and “discussions” about the advantages of UW3DI over “all sorts of Icoms and Kenwoods.”

The author of the article is pleased by the fact that less and less talk is heard on the bands about problems when working on the air with transistor power amplifiers (for example, the appearance of TVI or low reliability of output transistors). I competently declare that if a transistor amplifier is correctly designed and competently manufactured, and during operation the maximum operating modes of radio elements are not constantly exceeded, then it is practically “eternal”, theoretically, nothing can break in it.

I draw your attention to the fact that if the maximum permissible parameters of the transistors are not constantly exceeded, they will never fail. Short-term overload, especially transistors designed for linear amplification in the HF range, can withstand quite easily. Manufacturers of high-power RF transistors check the reliability of the manufactured product in this way - they take a resonant RF amplifier, and after the optimal mode and rated power are set at the output, a test device is connected instead of the load. Setting elements allow you to change the active and reactive components of the load.

If in optimal mode the load is connected to the transistor under test through a line with a characteristic impedance of 75 Ohms, then usually in the device under consideration the line segment is closed by a resistor with a resistance of 2.5 or 2250 Ohms. In this case, the SWR will be equal to 30:1. This SWR value does not allow obtaining conditions from a complete open circuit to a complete short circuit of the load, but the actually provided range of changes is quite close to these conditions.

The manufacturer guarantees the serviceability of transistors intended for linear amplification of the HF signal with a load mismatch of 30:1 for at least 1 s at rated power. This time is quite enough for the overload protection to operate. Operating a power amplifier at such SWR values ​​does not make sense, because the efficiency is practically “zero”, i.e. We are, of course, talking about emergency situations.

To solve the problem of matching transmitting and receiving equipment with antenna-feeder devices, there is a fairly cheap and simple way - using an additional external matching device. I would like to focus the attention of happy users of “bourgeois” equipment that does not have antenna tuners (and amateur designers too) on this very important issue.

All industrial transmitting and receiving equipment (including lamp equipment) is equipped not only with filtering, but also, additionally, with matching units. Take, for example, tube radio stations R-140, R-118, R-130 - their matching devices occupy at least a quarter of the station’s volume. And all transistor broadband transmission equipment, without exception, is equipped with such matchers.

Manufacturers even go to the extent of increasing the cost of this equipment - they are equipped with automatic control systems (tuners). But this automation is intended to protect the radio equipment from a stupid user who has a vague idea of ​​what and why he should turn on the control system. It is assumed that a radio amateur with a call sign must have a minimal understanding of the processes occurring in the antenna-feeder device of his radio station.

Depending on what antennas are used at the amateur radio station, one or another matching device can be used. The statement of some shortwave operators that they use an antenna whose SWR is almost unity on all bands, so that SU is not required, shows a lack of minimal knowledge on this topic. No one has yet managed to deceive “physics” here - no high-quality resonant antenna will have the same resistance either within the entire range, much less on different ranges.

What happens most often is that either an “inverted-V” is installed at 80 and 40 m, or a frame with a perimeter of 80 m, and in the worst case, the clothesline is used as an “antenna”. Particularly “talented” ones invent universal pins and “carrots”, which, according to the categorical assurances of the authors, “work on all ranges with virtually no adjustment!”

Such a structure is configured at best on one or two bands, and everyone goes ahead, “we call and they answer, what else is needed?” It’s sad that to increase the “operating efficiency” of such antennas, all searches lead to “radio extenders” such as the output unit from the R-140 or R-118. Just listen to those who like to “work in a group at a distance” at night on the 160 and 80 meter bands, and recently this can already be seen on 40 and 20 meters.

If the antenna has SWR = 1 on all bands (or at least on several) - this is not an antenna, but an active resistance, or the device that measures SWR “shows” the ambient temperature (which is usually constant in the room).

I don’t know whether or not I managed to convince the reader that it is mandatory to use a control system, but, nevertheless, I will move on to the description of specific circuits of such devices. Their choice depends on the antennas used at the radio station. If the input impedances of radiating systems do not fall below 50 Ohms, you can get by with a primitive L-type matching device - Fig. 1, because it only works in the direction of increasing resistance. In order for the same device to “lower” the resistance, it must be turned on in reverse, i.e. swap input and output.

Automatic antenna tuners of almost all imported transceivers are made according to the circuit shown in Fig. 2. Antenna tuners in the form of separate devices are often manufactured by the company according to a different scheme (Fig. 3). A description of this scheme can be found, for example, in. All branded control systems made according to this scheme have an additional frameless coil L2, wound with wire with a diameter of 1.2...1.5 mm on a mandrel with a diameter of 25 mm. Number of turns - 3, winding length - 38 mm.

Using the last two circuits, you can provide SWR = 1 to almost any piece of wire. However, do not forget - SWR = 1 indicates that the transmitter has an optimal load, but this in no way means high efficiency of the antenna. Using the control system, the diagram of which is shown in Fig. 2, it is possible to match the probe from the tester as an antenna with SWR = 1, but, except for its closest neighbors, no one will evaluate the efficiency of such an “antenna”. A regular P-circuit can also be used as a control system - Fig. 4. The advantage of this solution is that it is not necessary to isolate the KPI from the common wire; the disadvantage is that with high output power it is difficult to find variable capacitors with the required gap.

When using more or less tuned antennas at a station and in the case when operation on 160 m is not intended, the inductance of the SU coil may not exceed 10...20 μH. It is very important that it is possible to obtain small inductances up to 1 ... 3 μH.

Ball variometers are usually not suitable for these purposes, because the inductance is adjusted within smaller limits than in coils with a “slider”. Branded antenna tuners use coils with a “runner”, in which the first turns are wound with an increased pitch - this is done to obtain small inductances with maximum quality factor and minimal interturn coupling.

Sufficiently high-quality matching can be obtained by using the “poor radio amateur’s variometer” in the control system. These are two series-connected coils with tap switching (Fig. 5). The coils are frameless and contain 35 turns of wire with a diameter of 0.9...1.2 mm (depending on the expected power), wound on a 020 mm mandrel.

After winding, the coils are rolled into a ring and soldered with taps to the terminals of conventional ceramic switches with 11 positions. Taps for one coil should be made from even turns, for the other - from odd turns, for example - from 1,3,5,7,9,11, 15,19, 23, 27 turns and from 2,4, 6, 8 ,10, 14,18,22,28,30th orbits. By connecting two such coils in series, you can use switches to select the required number of turns, especially since the accuracy of selecting the inductance is not particularly important for the control system. The "poor radio amateur's variometer" copes successfully with the main task - obtaining small inductances.

In order for this homemade tuner to approach “bourgeois” antenna tuners in its quasi-smooth tuning capabilities, for example, AT-130 from ICOM or AT-50 from Kenwood, instead of one biscuit switch, it will be necessary to introduce short-circuiting of the coil taps with “relays”, each of which will be switched on separately toggle switch. Seven “relays” switching seven taps will be enough to simulate a “manual AT-50”.

An example of relay switching of coils is given in. The gaps between the plates in the KPI must withstand the expected stress. If low-resistance loads are used, with an output power of up to 200...300 W, you can get by with the KPI from older types of RPU. If they are high-resistance, you will have to select KPI with the required clearances (from industrial radio stations).

The approach to choosing KPI is very simple - 1 mm of gap between the plates can withstand a voltage of 1000 V. The estimated voltage can be found using the formula U = Ts P/R, where:

P - power,

R - load resistance.

The radio station must have a switch installed, with which the transceiver is disconnected from the antenna in the event of a thunderstorm (or when it is turned off), because More than 50% of cases of transistor failure are associated with static electricity. The switch can be mounted either in the antenna switch or in the control system.

U-shaped matching device

The result of various experiments and experiments on the topic discussed above was the implementation of a U-shaped “matcher” - Fig. 6. Of course, it is difficult to get rid of the “complex circuit of bourgeois tuners” Fig. 2 - this circuit has an important advantage, namely that the antenna (at least the central core of the cable) is galvanically isolated from the transceiver input through the gaps between the KPI plates. But an unsuccessful search for suitable KPIs for this scheme forced us to abandon it. By the way, the P-circuit circuit is also used by some companies that produce automatic tuners, for example, the American KAT1 Elekraft or the Dutch Z-11 Zelfboum.

In addition to matching, the P-circuit also acts as a low-pass filter, which is very useful when working on overloaded amateur radio bands - hardly anyone will refuse additional harmonic filtering. The main disadvantage of the U-shaped matching device circuit is the need to use a KPI with a sufficiently large maximum capacity, which suggests the reason why such a circuit is not used in automatic tuners of imported transceivers. In T-shaped schemes, two KPIs are most often used, rearranged by motors. It is clear that a 300 pF KPI will be much smaller, cheaper and simpler than a 1000 pF KPI.

In the control system circuit shown in Fig. 6, KPIs with an air gap of 0.3 mm from the tube receivers are used. Both sections of the capacitor are connected in parallel. A coil with taps switched by a ceramic biscuit switch is used as inductance.

The coil is frameless and contains 35 turns of wire 00.9...1.1 mm, wound on a mandrel 021...22 mm. After winding, the coil is rolled into a ring and soldered to the terminals of the biscuit switch with its short taps. Branches are made from 2, 4, 7, 10, 14, 18, 22, 26 and 31 turns.

The SWR meter is made on a ferrite ring. The permeability of the ring when working on KB, in general, is not of decisive importance; in the author’s version, a 1000NN ring with an outer diameter of 10 mm is used.

The ring is wrapped in thin varnished fabric, and then 14 turns of PEL 0.3 wire are wound around it (without twisting, in two wires). The beginning of one winding, connected to the end of the second, forms the middle terminal.

Depending on the required task (more precisely, on how much power is supposed to be passed through the control system, and on the quality of the LEDs VD4 and VD5), silicon or germanium detection diodes VD2 and VD3 can be used. By using germanium diodes, higher sensitivity can be obtained. The best of them is GD507. However, the author uses a transceiver with an output power of at least 50 W, so ordinary KD522 silicon diodes work perfectly in the SWR meter.

As a “know-how”, in addition to the usual one, an LED setting indication is used on the pointer device. A green LED VD4 is used to indicate the “forward wave”, and a red LED (VD5) is used to visually monitor the “reverse wave”. As practice has shown, this is a very successful solution - you can always quickly respond to an emergency situation. If something happens to the load while on air, the red LED begins to flash brightly in time with the emitted signal.

It is less convenient to navigate by the SWR meter needle - you won’t be constantly staring at it during transmission! But the bright glow of red light is clearly visible even with peripheral vision. This was positively appreciated by Yuri, RU6CK, when he got such a control system (besides, Yuri has poor eyesight). For more than a year now, the author himself has been using mainly only the “LED setting” of the control system, i.e. Setting up the “coordinator” comes down to making the red LED go out and the green LED “blazing” brightly. If you really want a more precise setting, you can “catch” it using the microammeter needle. The M68501 device with a total deviation current of 200 μA was used as a microammeter. You can also use the M4762 - they were installed in the Nota and Jupiter tape recorders. It is clear that C1 must withstand the voltage supplied by the transceiver to the load.

Tuning of the manufactured device is carried out using an equivalent load, which is designed to dissipate the output power of the cascade. We connect the control system to the transceiver with a “coaxial” of minimum length (as far as possible, since this section of cable will be used in the further operation of the control system and transceiver) with the required characteristic impedance; we connect an equivalent load to the output of the control system without any “long cords” and coaxial cables , turn all the control knobs to minimum and use C1 to set the minimum readings of the SWR meter during “reflection”. It should be noted that the transmitter output signal must not contain harmonics (i.e. it must be filtered), otherwise the minimum may not be found. If the design is made correctly, the minimum is obtained with capacity C1 close to the minimum.

Then we swap the input and output of the device and check the “balance” again. We carry out testing on several ranges. I warn you right away that the author is not able to help every radio amateur who could not cope with setting up the described control system. If someone is unable to make a control system on their own, you can order a finished product from the author of this article. All information can be found here.

LEDs VD4 and VD5 must be chosen modern, with maximum brightness. It is desirable that LEDs have maximum resistance when the rated current flows. The author managed to purchase red LEDs with a resistance of 1.2 kOhm and green LEDs with a resistance of 2 kOhm. Usually green LEDs glow weakly, but this is not bad - after all, it is not a Christmas tree garland that is being made. The main requirement for a green LED is that its glow should be quite clearly noticeable in normal transmission mode. But the color of the red LED, depending on the user’s preferences, can be selected from poisonous crimson to scarlet.

As a rule, such LEDs have a diameter of 3...3.5 mm. To make the red LED glow brighter, the voltage was doubled - diode VD1 was introduced into the circuit. For this reason, our SWR meter can no longer be called an accurate measuring device - it overestimates the “reflection”. If you want to measure accurate SWR values, you need to use LEDs with the same resistance and make the two arms of the SWR meter exactly the same - either both with voltage doubling, or without doubling. However, the operator is more likely to be concerned about the quality of the matching of the transceiver-antenna circuit, rather than the exact value of the SWR. LEDs are quite sufficient for this.

The proposed control system is effective when working with antennas powered through a coaxial cable. The author tested the control system for “standard”, common antennas of “lazy” radio amateurs - “frame” with a perimeter of 80 m, “inverted-V” - combined 80 and 40 m, “triangle” with a perimeter of 40 m, “pyramid” for 80 m.

Konstantin, RN3ZF, (he has an FT-840) uses such a control system with a “pin” and “inverted-V”, including on the WARC bands, UR4GG - with a “triangle” on 80 m and the “Volna” and “Volna” transceivers Danube", and UY5ID, using the described control system, matches the silo on the KT956 with a multilateral frame with a perimeter of 80 m with symmetrical power supply (an additional transition to symmetrical load is used).

If, when setting up the control system, it is not possible to turn off the red LED (to achieve the minimum readings of the device), this may mean that, in addition to the main signal, the emitted spectrum contains harmonics (the control system is not able to provide matching at several frequencies simultaneously). Harmonics, which are located higher in frequency than the main signal, do not pass through the low-pass filter formed by the elements of the control system, are reflected, and on the way back they “ignite” the red LED. The fact that the control system “cannot cope” with the load can only be indicated by the fact that coordination occurs at extreme values ​​(not minimum) of the parameters of the control unit and coil, i.e. when there is not enough capacitance or inductance. None of the indicated users experienced such cases when operating the control system with the listed antennas on any of the bands.

The control system was tested with a “rope”, i.e. with a wire antenna 41 m long. It should not be forgotten that the SWR meter is a measuring instrument only if there is a load on both sides of it at which it was balanced. When setting to “rope”, both LEDs light up, so the tuning criterion can be taken as the brightest possible glow of the green LED with the minimum possible brightness of the red one. Apparently, this will be the most correct setting - for maximum power transfer to the load.

I would like to draw the attention of potential users of this control system to the fact that under no circumstances should the coil taps be switched when emitting maximum power. At the moment of switching, the coil circuit breaks (albeit for a fraction of a second), and its inductance changes sharply. Accordingly, the contacts of the biscuit switch burn out and the load resistance of the output stage changes sharply. It is only necessary to switch the slide switch in receive mode.

Information for meticulous and “demanding” readers - the author of the article is aware that the SWR meter installed in the control system is not a precision high-precision measuring device. Yes, such a goal was not set during its manufacture! The main task was to provide the transceiver with broadband transistor stages with an optimal matched load, I repeat once again - both the transmitter and the receiver. The receiver, like a powerful silo, fully requires high-quality coordination with the antenna!

By the way, if in your “radio” the optimal settings for the receiver and transmitter do not coincide, this indicates that the device was not properly configured at all, and if it was done, then most likely only the transmitter, and the receiver’s bandpass filters have optimal parameters for other load values.

An SWR meter installed in the control system will show that by adjusting the elements of the control system we achieved the parameters of the load that was connected to the ANTENNA output of the transceiver during its configuration. Using the control system, you can safely work on the air, knowing that the transceiver is not “puffing up and begging for mercy,” but has almost the same load for which it was configured. Of course, this does not mean that the antenna connected to the control system began to work better. Don't forget about it!

For radio amateurs dreaming of a precision SWR meter, I can recommend making it according to the diagrams given in many foreign serious publications, or buying a ready-made device. But you will have to fork out some money - indeed, devices produced by well-known companies cost from 50 USD and above CB - I don’t take into account the fancy Polish-Turkish-Italian ones. A successful, well-described design of an SWR meter is given in.

A. Tarasov, (UT2FW) [email protected]

Literature:

1. Bunin S.G., Yaylenko L.P. Shortwave Radio Amateur's Handbook. - K.: Technology, 1984.
2. M. Levit. Device for determining SWR. - Radio, 1978, N6.
3. http://www.cqham.ru/ut2fw/

For example, the input impedance of RA with OS:

on GK-71 about 400 Ohms;

on GU-81 about 200-1000 Ohms.

(Data taken from descriptions of RA designs in amateur radio literature).

3.5 MHz – 77 Ohm;

7 MHz – 128 Ohm;

14 MHz – 102 Ohm;

21 MHz – 54 Ohm;

28 MHz – 88 Ohm.

From the given figures it is clear that coordination of the transceiver with the RA is clearly necessary. Typically, such matching is performed using either parallel LC circuits or P-circuits installed at the lamp input. The method is certainly good, it provides matching with an SWR of no worse than 1.5, but it requires 6-9 circuits and two switch bars.

In foreign military, civilian, and amateur radio equipment, broadband HF transformers have long been widely used to match 50-ohm units. They make it possible to coordinate these blocks with other circuits with a resistance that differs from 50 Ohms and lies in the range of 1 - 500 Ohms. Such broadband RF matching transformers can also be used to match transceivers with PA. They are small in size and you can always find a place to place them in the body (in the basement of the chassis) of the old RA.

In Fig. 1a. a diagram of an HF transformer on a toroidal ferrite core with a transformation ratio of

oppositions 1 ׃ │≥ 1…≤ 4 │ , depending on the connection point of the output tap.

For transceiver output power up to 100 W, two 32 x 16 x 8 ferrite rings with a permeability of about 1000, or a larger diameter, but not with a smaller cross-section of the core, can be used as a toroidal core.

When this transformer is turned on according to the first option (with the middle winding turned off), the output resistance is transformed into the following values: 50.70, 80, 90, 100, 120, 140, 170, 200 (Ohm). SWR on all bands (across all taps) is no more than 1.4.

2. The transformer with twisted wires showed the best results. The output resistances are the same as those of the first transformer, but the SWR is much lower: on the ranges 3.5; 7: 14 MHz no more than 1.2; at 21 MHz – no more than 1.4; at 28 MHz – 1.5 - 1.65. When the transformer is turned on according to the first scheme, the SWR is even better.

The transformer is connected to the gap between the input connector RA and the transition capacitor going to the lamp (to the cathode). If possible, you need to install a biscuit switch. In this case, you will need to select 2 - 3 positions at which the lowest SWR will be obtained on all bands. If this is not possible, then you will have to look for a compromise; you will need to find one tap from the transformer winding with an acceptable SWR on all ranges. Select a tap and measure the SWR for the RA to operate in operating power mode.

To match the transceiver with the RA, you can use simple matching devices based on a G-filter according to the diagram in Fig. 2, in the form of a separate unit connected between the transceiver and the RA with short sections of RF cables. (Possible with built-in SWR meter).

Fig.2

But control systems in the form of a separate block have a significant drawback: in the reception mode, when the “bypass” is turned on in the RA, the output of the control system turns out to be mismatched with the antenna. However, this does not significantly affect the level of the received signal, because Usually the low-resistance antenna resistance is loaded onto the higher-resistance, now (for the antenna) input of the control system.