Simple antenna amplifier. Transistor power amplifier

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Ultrashort wave amplifiers

The VHF power amplifier is designed to operate at frequencies above 100 MHz. It is waves with a similar frequency that are ultrashort. It is worth noting that not all frequencies of this type are publicly available. Some of them are allowed to be used only in emergency situations (146 - 200 MHz frequencies of city services). Many, for example, 145 MHz are publicly available, but many are also used for communication with the ISS, satellites, ships, aircraft, etc.
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The more I understand the modern element base, the more I am amazed at how easy it is now to make electronic devices that previously could only be dreamed of. For example, the antenna amplifier in question has an operating frequency range from 50 MHz to 4000 MHz. Yes, almost 4 GHz! In the days of my youth, one could simply dream of such an amplifier, but now even a novice radio amateur can assemble such an amplifier on one tiny microcircuit. Moreover, he has no experience working with ultra-high-frequency circuitry.
The antenna amplifier presented below is extremely simple to manufacture. It has good gain, low noise and low current consumption. Plus a very wide range of work. Yes, it is also miniature in size, thanks to which it can be embedded anywhere.

Where can I use a universal antenna amplifier?

Yes, almost anywhere in the wide range of 50 MHz - 4000 MHz.

- As a TV antenna signal amplifier for receiving both digital and analogue channels.
- As an antenna amplifier for an FM receiver.
- etc.

This applies to domestic use, but in the amateur radio field there are much more applications.

Antenna amplifier characteristics

Operating range: 50 MHz – 4000 MHz.
Gain: 22.8 dB - 144 MHz, 20.5 dB - 432 MHz, 12.1 dB - 1296 MHz.
Noise figure: 0.6 dB - 144 MHz, 0.65 dB - 432 MHz, 0.8 dB - 1296 MHz.
Current consumption is about 25 mA.

More detailed characteristics can be found in.
The low noise amplifier has proven itself to be excellent. The low current consumption is fully justified.
The microcircuit also perfectly withstands high-frequency overloads without loss of characteristics.

Making an antenna amplifier

Scheme

The circuit uses an RFMD SPF5043Z microcircuit, which can be purchased at -.
In fact, the entire circuit is an amplifier microcircuit and a filter for its power supply.

Amplifier board

The board can be made from foil PCB, even without etching, as I did.
We take two-sided foil-coated PCB and cut out a rectangle measuring approximately 15x20 mm.

Then, using a permanent marker, draw the layout along the ruler.

And then you want to etch, or you want to cut out the tracks mechanically.

Next, we tin everything with a soldering iron and solder SMD elements of size 0603. We close the bottom side of the foil board to a common wire, thereby shielding the substrate.

Setup and testing

No adjustment is required; you can, of course, measure the input voltage, which should be within 3.3 V and the current consumption is approximately 25 mA. Also, if you operate in the range above 1 GHz, you may need to match the input circuit by reducing the capacitor to 9 pF.
We connect the board to the antenna. The test showed good gain and low noise level.

It will be very good if you place the board in a shielded case, like this.

You can buy a board for a ready-made amplifier on, but it costs several times more than a separate microcircuit. So it’s better to get confused, it seems to me.

Schema addition

To power the circuit, a voltage of 3.3 V is required. This is not entirely convenient, for example, if you use the amplifier in a car with an on-board voltage of 12 V.

For these purposes, you can introduce a stabilizer into the circuit.

Connecting the amplifier to the antenna

In terms of location, the amplifier should be located in close proximity to the antenna.
To protect against static and thunderstorms, it is desirable that the antenna be DC-switched, that is, you need to use a loop or frame vibrator. An antenna like "" would be an excellent option.

Current consumption - 46 mA. The bias voltage V bjas determines the output power level (gain) of the amplifier

Fig. 33.11. Internal structure and pinout of TSH690, TSH691 microcircuits

Rice. 33.12. Typical inclusion of TSH690, TSH691 microcircuits as an amplifier in the frequency band 300-7000 MHz

and can be adjusted within 0-5.5 (6.0) V. The transmission coefficient of the TSH690 (TSH691) microcircuit at a bias voltage V bias = 2.7 V and a load resistance of 50 Ohms in a frequency band up to 450 MHz is 23 (43) dB, up to 900(950) MHz - 17(23) dB.

Practical inclusion of TSH690, TSH691 microcircuits is shown in Fig. 33.12. Recommended element values: C1=C5=100-1000 pF; C2=C4=1000 pF; C3=0.01 µF; L1 150 nH; L2 56 nH for frequencies not exceeding 450 MHz and 10 nH for frequencies up to 900 MHz. Resistor R1 can be used to regulate the output power level (can be used for an automatic output power control system).

The broadband INA50311 (Fig. 33.13), manufactured by Hewlett Packard, is intended for use in mobile communications equipment, as well as in consumer electronic equipment, for example, as an antenna amplifier or radio frequency amplifier. The operating range of the amplifier is 50-2500 MHz. Supply voltage - 5 V with current consumption up to 17 mA. Average gain

Rice. 33.13. internal structure of the ΙΝΑ50311 microcircuit

10 dB. The maximum signal power supplied to the input at a frequency of 900 MHz is no more than 10 mW. Noise figure 3.4 dB.

A typical connection of the ΙΝΑ50311 microcircuit when powered by a 78LO05 voltage stabilizer is shown in Fig. 33.14.

Rice. 33.14. broadband amplifier on the INA50311 chip

Shustov M. A., Circuitry. 500 devices on analog chips. - St. Petersburg: Science and Technology, 2013. -352 p.

In this article I will describe the methodology for selecting, remaking and customizing industrial samples of products with which I have repeatedly worked. Of all the criteria, the most fully described and, most importantly, easily repeatable option will be taken.

Chapter 1. Method for selecting the type of amplifier.

There are two ways to approach this problem. The first way is a completely homemade finished structure. The second way is when the amplifier is based on an industrial design of the most critical design unit, and further work is carried out independently. Let's focus on this option. The main part in the original design, with an output power of up to 1 kW, is the resonator, as the most complex and critical component.

Let's consider the advantages of an industrial design.

Professionally turned on lathe and milling equipment with great precision.
Large mass due to the thick walls of the resonator, which improves the mechanical, temporal and frequency stability of the parameters.
High quality factor.
Inhomogeneity and scattering of the field into the surrounding space are reduced to a minimum.
The components for setting it up and connecting it to the antenna are professionally and precisely made.

Flaws:

As a consequence of the above, it is weight and the ability to be transported quickly and easily.
Difficult to acquire, there are fewer and fewer of them every day.

I will not consider the case with transistor amplifiers because even according to preliminary estimates, it is three to four times more expensive, and the “whims” of the module are great. Strict requirements for the power supply at low voltages and high currents. Protection must be fast, and, if possible, against everything that can be foreseen. When adding output power (not bad when dividing input power), it is advisable to use a circulator for each module. Addition bridges with ballast loads are also needed to absorb the reflected signal, then we can still talk about the reliability of the amplifier. In my opinion, today it is even easier to solve the problem using a lamp.

Having studied the assortment of different blocks and remade a sufficient number of copies, it turns out that the choice is extremely small. The best example is the power amplifier from TRRS R-410M(M1). For this purpose, block 310B of rack 300BM1 is ideally suited. Power amplifier blocks from aviation radio stations R-824, R-831M (R-831 is not suitable at all), R-834(M), R-844M, Sprut-1 have similar parameters. The experience of restructuring shows that it is much easier to lower the resonance frequency than to increase it, as required by the above aviation radio stations. They are designed in such a way that this is a big problem. The technical specifications for these radio stations already allow for a reduction in output power at the HF edge of the range (389.975 MHz). The design of the resonator, although simpler, still has a separation capacitance in the anode, and this is not the best solution. The RF choke in the anode will also add its own capacitance. In addition, a corrective inductance (in the R-831M) is also included in the anode, designed to equalize the load characteristics of the lamp, and this also adds additional capacitance to the resonator. With such a set of capacitances, it is no longer possible to tune the resonator to 432 MHz, despite the fact that all unnecessary low-pass filters are disabled. The designers had great difficulty reaching 390 MHz. So aviation radios are not the best solution to the problem for 432 MHz.

Let's return to the R-410M(M1). Developed at MNIRTI, it was produced at the Vladimir Elektropribor plant for almost 30 years, until 1989. During this time, 11 series of radio stations (changes and modifications) were produced.

The 300BM1 rack is a power amplifier rack. In the output stage of the rack there are 2 amplifier blocks 310B on the left and 2 blocks 310B on the right. They are rocked by one block 310B, in turn these blocks are rocked by blocks 320B. The stand operates on two parabolas with horizontal and vertical polarization each. The principle of dual and quadruple reception and transmission is used. In the FM mode, the 310B block delivers 650 W (each) for a long time, this is determined by the protection installed at the factory (block 330 - anode power supply and its protection), with an anode current of 0.4-0.5 A (this mode is recommended by the manufacturer as a mode lamp life, according to reference data). The adjustment is operational, using a potentiometer, up to a maximum anode current of no more than 0.9 A (anode voltage + 2500 V). This is a standard power supply.

So, the 310B block is assembled on a GS-35B lamp according to a scheme with a common grid. Anode voltage +2500 V, anode current 0.7 A, output power about 1 kW. The resonator is smoothly tuned in two ranges.

476 - 525 MHz. (channels 1 to 50)
576 - 625 MHz. (channels 51 to 100)

Resistors R1 and R2 in the cathode circuit create a bias on the lamp grid, but the initial anode current is not large, because World Cup mode was used. With an output power close to 1 kW, to increase efficiency. and reducing swing (with an old lamp), it may be necessary to increase the initial anode current, reducing the value of R1 and R2 to 100-120 Ohms each. But it is best to replace the resistors in the cathode with a chain of zener diodes of the D-815A type. They can easily select the desired initial anode current and ensure that the lamp is turned off during reception (there are a huge number of similar circuits in amplifiers). Resistor R6 is connected to the cathode circuit by the contacts of relay P1, when 27 V is supplied to it. The “work” - “hardening” toggle switch is in the hardening position, and the lamp is locked. The toggle switch is located in block 320 and at the same time from block 330 (anode power supply), only half of the anode voltage is supplied to the lamp anode from the midpoint of the anode transformer (+1250 V). Thus, one half-set can be used at a time for training lamps, which is often done. Resistor R4 is a shunt when measuring the anode current, and R3 is a shunt when measuring the grid current. The anode power supply (block 330) has current protection in the range of 0.4-0.9 A. with operational adjustment.

The resonators of block 310B have the following design. Both resonators are directed in one direction, towards the cathode - this is the best arrangement (unlike aviation radio stations, where the anode resonator is directed in the other direction).

The anode-grid resonator (anode) has a length of about a quarter of the wavelength. The cathode grid resonator (cathode) is about three-quarters of the wavelength long. Only with this combination of resonator lengths can feedback circuits (FOC) be introduced, increasing the stability of the amplifier; at both lengths of a quarter wave, this cannot be done; such amplifiers are prone to self-excitation. Amplifier load 75 Ohm. For a load of 50 Ohms, it is necessary to connect a half-wave section of the 75 Ohm cable between the amplifier and the 50 Ohm cable, because a half-wave section of cable “transmits” a load of 50 Ohms from one end of the cable to the other, i.e. to the amplifier and the matching will be as required.

Advantages of one-sided resonator design:

You don't need a stable, high-voltage, microwave isolation capacitor with good TKE in the lamp anode. It introduces losses and degrades the characteristics of the resonator.
There is no need for an anode choke, which adds its own capacitance to the resonator, which is also bad.
The massive radiator of the lamp is not under HF potential and does not in any way affect the tuning of the resonator (which cannot be said about aviation radio stations, where the massive radiator has a large capacitance in the anode and it is no longer possible to increase the frequency of the resonator). The leakage of the RF field through the radiator is minimized, which makes it easier to blow around the lamp.
The anode is grounded at HF using the simplest structural container made of fluoroplastic tape, and power is supplied directly to the anode of the lamp.

This design allows you to make full use of the RF properties of the lamp, which makes setup easier.

Chapter 2. Tuning the resonator, block 310B to a frequency of 432 MHz.

Remaking the block is so simple that it can be done by any person who knows how to work with their hands and will treat it carefully. The method described below is very simple, it is not exclusive, it is widely known to many radio amateurs and approved by them, I am only systematizing it in this article based on my experience.

Only the anode resonator is subject to modification. The tuning frequency of the anode resonator needs to be shifted slightly downward in frequency. To do this, you need to lengthen it a little or add a small adjustable capacitance to the resonator. It is easier to lengthen the resonator. The experience of remaking many copies shows that it is enough to lengthen it by 14-18 mm. To do this, it is necessary to turn the anode plunger in the opposite direction and the length of the anode chamber will increase. At the same time, in order for the plunger to move as far back as possible (towards the input connector) and rest against the centering washer of the anode resonator, the three rods driving the plunger must be shortened by exactly 20 mm. This must be done slowly and carefully. Unfold the plunger and reassemble the resonator in reverse order. The general view of the block is shown in photo 1 and photo 2.

2.1. Resonator disassembly sequence.

Unsolder the filament (green) and cathode (yellow) wires from the unit support post. Photo 3 shows the outer part of the anode resonator.

1. Anode flange 5, steel, next to it is a sealing stocking made of braided shielded wire (reduces RF field leakage).

2. Take out the anode ring 7 (current collection) with the anode separation capacitance C1, made of fluoroplastic -4 (according to technical specifications), pos. 6 and pos. 8. Handle 8 with care - this is a 0.28 mm thick ring made up of 14 chords (half rings) each 0.02 mm thick. If some of them are torn, which happens quite often when the lamp is removed without a puller, cut out new ones.
P.S. There are two different designs for this anode part.

3. Unscrew the four M3 screws and remove the antenna probe 10 with connector from the anode cylinder 9.

4. At the back of anode cylinder 9, unscrew six M4x15 screws (from the end) and slowly pull it forward (towards container C1).
P.S. There are two mounting options, not only from the rear end, but also from the side with M3x10 screws.
A section of the outer part of the anode resonator is shown in Fig. 1.

5. On the grid resonator 11 (the internal cavity of the anode resonator) two negative feedback loops (NFLs) are visible, which is necessary to increase the stability of the amplifier from self-excitation. Handle the loops carefully, see photo 4.

6. Rotating the anode adjustment gear, lower plunger 12 almost close to the OOS loops. Next, use a powerful screwdriver to unscrew the three M4x12 countersunk screws on the gearbox and release the rods 14 from the gearbox, see photo 5.

7. Unscrew the grid resonator from the cathode resonator using five M3x10 screws in the rear part, at the input connector, around the perimeter.
P.S. There are two versions of this rear part of the resonator.

8. Unscrew the three M3x10 screws holding the centering washer 13 of the anode resonator, see Fig. 2 and photo 5, so that it is in a free position. Mark it on the outside with a mark so that you can see how it stood before for reassembly. If washer 13 is not unscrewed, then when you remove the grid resonator, the tips of the screws can cut the fluoroplastic washer 16. Take this into account when reassembling.

9. Slowly pull the grid resonator forward (towards the lamp).
Figure 2 shows a cross-section of the grid resonator.

10. So the mesh cylinder is released, see Fig. 2. and photo 5. It shows that plunger 12 is directed backwards by sliding contacts (towards the gearbox). Next, unscrew, rotating along the axis, rods 14 from plunger 12. Take out washer 13 back (towards the gearbox), then plunger 12. So the unit is disassembled, see photo 6.

11. Wash everything that has been disassembled (except for the inside of the cathode resonator). Take different flute brushes and wash everything with soap and water. Resonators should shine. Where the eaten points are marked on the body, carefully use a scalpel to scrape them out and deep scratches too. Next, but not much, very soft and preferably with a good imported eraser, polish them and the oxides too. Don't rub too much, just a little. This is necessary so that when adjusting the plunger does not add more scratches to you.

12. Cathode resonator 15 cm. Photo 7. can be cleaned with cotton wool soaked in alcohol using a thin long screwdriver. There is a worm inside to move its plunger.

Figure 3 shows a cross-section of the cathode resonator. It is about three-quarters of a wavelength long, and to reduce its size, it was folded in half. For ease of adjustment, both halves are placed coaxially, i.e. one inside the other, this makes it easier for the plunger to move. Only the internal part of the resonator is rebuilt, the external part is not rebuilt. The lamp is connected through capacitor C2 to their common point, i.e. almost to the middle of the three-quarter line, and the input connector is completely included in the line (resonator). If the worm works hard, then by moving it to the lamp, you can drop a little oil and drive it along its entire length. This must be done carefully, without damaging the fluoroplastic tape (capacitor C2). Be sure to check with a tester for a short circuit (some resistance) of the cathode to the housing; there should not be one.

Shorten rods 14 to a length of 20 mm (a little more is possible, but all three are synchronous) in any way convenient for you. It is necessary to take into account that they are made of tool steel grade 40X and are hardened (cemented) on the outside. Hardening depth is about 0.4 mm. Personally, I trim from the narrow side on a lathe with a carbide cutter, then grind it to a diameter of 4 mm. and cut the thread with a die, pressing it from behind. Three rods take about 40-60 minutes if you work slowly.

The resonator is assembled in the reverse order.

2.2. Resonator reassembly sequence.

Chapter 3. Final amplifier assembly.

When finalizing the amplifier, you need to decide how it will be used. It can be used with a separate feeder for transmission, or with one common feeder, according to the classical scheme. Both cases have their pros and cons. Each radio amateur decides for himself what to do.

Let's consider the first case with a separate feeder. If the feeder is 75 Ohm, then no questions arise here; we use direct connection. If the feeder is 50 Ohms, then between the amplifier and the rear (front) panel with antenna connectors, you need to solder sections of 75 Ohm cable, half a wavelength in the cable at a frequency of 432 MHz. (as well as the length of a multiple of half a wave - this is a wave, one and a half waves, etc.), but not a quarter wave. On the amplifier side, the cable is soldered to the standard 75 Ohm connectors, and on the rear panel to the connectors you need.

For a cable with continuous polyethylene insulation, the lengths of the segments are equal to:
228 mm. - half wave, 456 mm. - wave, 684 mm. - one and a half waves, etc.
For a cable with continuous fluoroplastic insulation, the lengths of the segments are equal to:
241 mm. - half wave, 482 mm. - wave, 723 mm. - one and a half waves, etc.

The soldered connectors fit into the length of the cable length.

The second case is with one feeder. If the feeder is 75 Ohm, then REV-15 relays with a classic switching circuit are used. If the feeder is 50 Ohm, then it is necessary to use the same sections of cables as in the case of one feeder. Next is the REV-15 relay, and again the same sections of cable from the relay to the rear panel. Between the relays there is the same 75 Ohm piece of cable. This option with the REV-15 relay is much cheaper than with a 50 Ohm cable and the REV-14 relay. At the same time, the coordination in both options does not differ from each other in any way. But in Moscow, at the Mitinsky radio market, there are a lot of REV-15 relays and you can buy them for 200 rubles, and you still need to look hard for the REV-14 relay and cheaper than 1500 rubles. difficult to find.

Cooling the amplifier is carried out as follows. At the back of the anode flange it is necessary to attach a turbine operating on suction from the lamp, with a capacity of at least 150-200 cubic meters per hour, but 250-280 cubic meters per hour is better. And it’s quite good if you also blow air with a small turbine into the cathode pipe. The air will pass through the cathode resonator and exit out of the grid resonator (cylinder on the sides). It is better to install it directly inside the resonator, discarding the flexible air duct. It is better to make the transition between the cathode nozzle and the turbine outlet gentle in order to exclude vortex flows inside that slow down the air movement.

In this article, I briefly summarized my work experience and my vision of the task in such amplifiers, but everyone has the right to make a decision at their own discretion.

I wish you success.

Alexander. RV3AS. e-mail: This e-mail address is being protected from spambots. To view it, you must have JavaScript enabled

The transistor power amplifier (SPA) has been proven and differs little in various industrial designs, which indicates the virtual absence of “blank spots” in this area of radio design. And yet, radio amateurs quite rarely use homemade designs at a power of more than 30-40 W. This, of course, is due to the scarcity of high-quality, powerful transistors for linear amplification of the RF signal in the range of 1-30 MHz.

It is also possible that the main method of tuning amateur equipment - the “scientific poking method” is not suitable for such designs, which is why tube amplifiers are more popular today. Repeated use of various types of transistors in silo transceivers has shown their clear advantages in comparison with tube ones of the same power (we are, of course, talking about Pout.< 200 Вт). При изготовлении и эксплуатации транзисторного усилителя нужно учитывать определенные особенности, которые не возникают либо менее выражены в ламповом. Вот некоторые из них:

1. You need to use transistors specially designed for linear amplification at frequencies of 1.5-30 MHz.

The output power of a push-pull silo should not exceed the maximum power value of the transistors used, although they can withstand overloads. For example, in military equipment this figure does not exceed 25-50% of the maximum value.
Look at the reference book at least once and carefully read the parameters of the transistor used.
None of the maximum permissible parameters must be exceeded.
During preliminary tuning, you should use a non-inductive load in the form of an equivalent resistance of 50-75 Ohms of the appropriate power, but in no case a light bulb, as many do when setting up a tube amplifier.
Finally, strain yourself and make once and for all a high-quality SWR meter in one box with an antenna switch and a TVI filter, with the obligatory disconnection of the antennas when not in use. In this way, you will save yourself from nervous stress when communicating with neighbors who love ultra-long-range television reception on an indoor antenna and hastily search for rubber gloves to unscrew the antenna connector at the beginning of each thunderstorm.
If you are infected with “arrow disease” or like to “hold the microphone” until “condensation” drips from it, you do not need to skimp on the size of the case and radiator. The axiom is “a reliable amplifier is a great amplifier.”

Otherwise, it is necessary to introduce additional airflow.

There is no need to take on the construction of such an amplifier if you vaguely imagine the difference between transformers of the “binoculars” type and those with a “volumetric turn”. In this case, it is better to purchase a ready-made design (the author of the article can help you with this) or improvise with lamps.

The transistor power amplifier proposed in this article operates in any part of the HF range; the matching device allows the use of antennas with a resistance of 50 Ohms or more (Fig.).

The pumping power does not exceed 1 W. The maximum output power is determined by the type of transistors used, for KT957A - up to 250 W. Power gain up to 25 dB in low frequency ranges. Input impedance 50 Ohm. The output harmonic level is no more than 55 dB.

The maximum current consumption is up to 18-19 A. Due to the fact that the radio station used one antenna for all bands (a triangle with a perimeter of 160 m), it was decided to introduce a matching device with an SWR meter into the amplifier. The overall dimensions of the amplifier were determined by the dimensions of the transceiver used (RA3AO) and are 160x200x300 mm. It was not possible to “fit” the +24 V source, which is made in a separate housing, into these dimensions. To ensure that the amplifier does not overheat in the summer, forced cooling of the radiator has been introduced. The result is a fairly successful design of small dimensions, which can be used when working with a low-power exciter, this could be a transceiver based on P399A, Rosa, RA3AO transceivers with reduced output power, etc. A similar design is used by RK6LB, UR5HRQ, and RU6MS has been operating the output stage on the KT956A with P399A for several years.

The signal from the transceiver goes to transformer T1 (Fig.),

this is an ordinary “binoculars” that lowers the input impedance and provides two identical antiphase signals at the driver input VT1, VT2. Chains C4R2 and C5R3 serve to form the amplitude-frequency response with a rise in the high-frequency region. The bias is applied separately to each transistor from a +12V source (TX). As VT1, VT2 you need to use transistors that serve to linearly amplify the RF signal. The most suitable and inexpensive are KT921 and KT955. If it is possible to match a pair, then the bias circuits can be combined. Negative feedback resistors in the emitter circuit improve the stability and linearity of the cascade.

The C10R10 “hole filter” can be replaced with several conventional blocking capacitors of different ratings (for example, 1000 pF; 0.01 μ; 0.1 μ), connected in parallel. Elements C14, C18, R11 ... R14 form the required frequency response of the output stage. Resistors R15, R18 serve to prevent breakdown of the emitter junction during the reverse half-wave of the control voltage. They can be calculated using the formula R = (βmin/(6.28*frp*C3) for other types of transistors. Transformer T2 (“binoculars”) matches the relatively high output resistance of the first stage with the lower resistance of the input circuits of the final stage.

The TZ transformer supplies power to VT4, VT5 and balances the voltage waveform at the transistor collectors in order to reduce the level of even harmonics. Additionally, using the circuit formed by winding II and capacitor C19, the amplifier’s frequency response is raised in the region of 24…30 MHz.

Output transformer T4 matches the low resistance of the output stage with a load resistance of 50 Ohms. Resistor R21 with a power dissipation of at least 2 W (it can be selected from several) has the symbol “foolproof”. The presence of this resistor is critical if there is no load on the amplifier. At such a moment, all the output power will be dissipated on this resistor and the “spirit of burnt paint” will come from it - the conclusion to a careless user is “we’re on fire!” Transistors can withstand such execution - according to the manufacturer, the degree of load mismatch at Pout = 70 W for one transistor for 1 s is 30:1. In our case, we have 10:1, so we can assume that nothing will happen to the transistors in 3 seconds. As experiments and many years of experience in using such “protection” have shown, transistors have never failed from output overload.

Even after a direct lightning strike on the antenna of one of the users of this technology, only one transistor failed, and resistor R21 crumbled into small pieces. Relay K1 switches the antenna in receive/transmit modes (RX/TX). It is advisable to use a new, reliable sealed relay with a short response time. K1 is turned on with a voltage of +12V (TX) through the transistor switch VT6. The bias circuit VT4,VT5 is combined, because it was possible to select pairs of these transistors, otherwise it is better to perform the bias circuits separately, as was done, for example, in. To temperature stabilize the quiescent current, it is desirable to ensure thermal contact of at least one of the diodes VD1, VD3 with the nearest transistor.

From the output of the amplifier, the signal is fed to the SWR meter (Fig.). The diagram of such devices (Fig.) has been repeatedly described in the literature.

It should only be noted that almost any ferrite ring can be used as the T1 core, regardless of permeability. As permeability increases, we reduce the number of turns of winding II. Trimmer capacitors C1 and C8 must withstand a voltage of at least 120 V and not change their parameters when heated.

The low-pass filter unit (AZ) (Fig. 4) consists of six 5th order low-pass filters, which are switched using a RES34 or RES10 relay. Their input and output load resistances are 50 Ohms. The data for these filters are shown in Table 1; they differ slightly from the calculated ones. This is due to the fact that the amplifier slightly detunes the filters and we had to additionally select elements at maximum output power. This is a rather risky undertaking, but the author does not know of any other real method of how to take into account, calculate and compensate for the influence of the amplifier on the low-pass filter in operating mode. The filters are switched by applying supply voltage to the relay from the SB2 “galetnik” (Fig. 1).

The filtered signal is fed to a matching device (Fig.), consisting of coils L1, L2 and capacitors C9, C10. With this circuit for connecting elements, matching with a load >50 Ohms is possible. This fully corresponded to the task at hand - to coordinate with a frame with a perimeter of 160 m. The input impedance of such an antenna was not less than 70 Ohms on any of the bands. If coordination with loads below 50 Ohms is required, you need to introduce another flip switch, which will allow you to change the device configuration. Or at least switch capacitor C10 from the output of the device to its input. It is very difficult to choose a variometer of suitable dimensions for such a design, and, moreover, with the ability to change the inductance within the range of 0...1 μH.

Ball variometers are not suitable because... rarely change inductance within small limits; coils with a “slider” have large dimensions. Therefore, the simplest option was used - a frameless coil, rolled into a ring and soldered with its leads onto the contact petals of a conventional ceramic biscuit switch with 11 positions. The taps of the coils are made differently in order to more accurately select the total inductance of the matching device. For example, L1 has 1, 3, 5, 7, 9, 13, 17, 21, 25, 30 turns, and L2 has 2, 4, 6, 8, 12, 16, 20, 24, 28, 32 turns . This discreteness will be enough to accurately select the required inductance.

For example, the antenna tuners of the Kenwood TS-50 and TS-940 transceivers use coils with seven taps. If the antenna resistance does not exceed 360...400 Ohms, you can leave one coil of 40...44 turns. The gap between the C10 plates should be at least 0.5 mm; capacitors from old tube radios will do. To operate at 160 m, and sometimes at 80 m, an additional capacitor C9 is connected.

When manufacturing an amplifier, you should pay attention to the quality of the parts and their electrical strength. The leads of elements in RF circuits must have a minimum length. If possible, you need to select pairs of transistors, at least using the simplest method.

For example, the transistors are given the same biases on the base, the collector currents are measured (at least at three different values of the bias voltages), and pairs of transistors are selected based on closer collector currents. Because The transistors are powerful, you need to carry out measurements by setting the collector currents to approximately 20...50 mA, 200...400 mA and 0.9...1.3 A, and apply a voltage to the collector close to the operating voltage, at least 18...22 V. Transistors with high currents will require a temporary heat sink or measurements must be carried out quickly, because As it warms up, the transistor's transconductance increases. It is better to use ceramic capacitors, tested in equipment, electrolytic capacitors - tantalum.

Chokes in the base circuits can be used of the DM, DPM types with minimal internal resistance so that additional auto-bias is not created on them, i.e. designed for high current (for the driver no less than 0.4 A, for output transistors no less than 1.2 A). It’s even better to wind them on ferrite rings with a diameter of 7...10 mm with a permeability of 600...2000; 5...10 turns of wire with a diameter of 0.4...0.7 mm will be enough. “Binoculars” were manufactured using “simplified technology”, i.e. Inside the columns of ferrite rings, a turn of silver braiding from the coaxial cable is stretched, and inside this braiding there is a secondary winding wire in heat-resistant insulation. No differences in the operation of such transformers from “binoculars” with copper tubes were noticed.

The transformer has better parameters when it is wound with twisted thin wires. For example, in an industrial PA on KT956A, this transformer is wound with a twist of 16 PEV-0.31 wires, divided into 2 groups of 8 wires. When choosing transistors for such an amplifier, first of all you need to pay attention to what purposes these transistors are intended for.

There will be no problems with TVI at maximum power if you use transistors designed for linear signal amplification in the range of 1 ... 30 MHz - these are KT921,927, 944, 950, 951,955, 956, 957, 980, etc. Such devices make it possible to obtain the maximum possible power without compromising reliability and with minimal nonlinearity. For such transistors, the coefficient of combination components of the third and fifth orders is normalized, and not every lamp can compete with them in these indicators.

The use of KT930, 931,970 and the like in such an amplifier does not make sense. In order not to overload the reader with unnecessary information about certain transistors, you only need to note that transistors designed for frequencies above 60 MHz, as a rule, are manufactured using a different technology and operate in class C, amplifying the frequency-modulated signal. When such transistors are used at frequencies below 30 MHz, they are prone to excitation and do not allow maximum power to be obtained due to a sharp decrease in reliability and increased TVI. Only KT971A work more or less tolerably, and even then at reduced power.

SETTING up the amplifier comes down to setting the quiescent currents - 300...400 mA on VT1, VT2 and 150...200 mA on VT4, VT5. This procedure is performed using R1, R4, which can be in the range of 390 Ohm...2 kOhm and R5 (680 Ohm...10 kOhm). If it is not possible to obtain the required currents, you can add one diode in series with VD2, VD4, and VD1, VD3.

The correct ratio of turns in the transformers at the expected maximum power is checked by connecting a low-pass filter and switching the load to the output of the filters. Having noticed the values of the output voltage and current consumption in the ranges of 28, 14, 3.5 MHz, change winding T4 by one turn II. It is necessary to leave such a number of turns when there are minimum current meter readings at maximum or the same output voltage values. As a rule, you can initially wind 3 turns, and during the setup process reduce it by one turn. We carry out a similar procedure with T1 and T2.

To compensate for gain unevenness, which is usually observed on different ranges, additional selection of C4, R2, C5, R3, R11,…R14, C14, C18 may be required. If the transistors have not been previously selected, it is advisable to adjust the quiescent currents to maximize the suppression of even harmonics, the level of which is monitored by a spectrum analyzer or receiver.

The PRINTED BOARD (Fig.) is made of double-sided fiberglass with a thickness of at least 1.2 mm using a sharp knife, a metal ruler and a cutter for cutting contact “spots”.

At the bottom of the board, some “spots” are connected to each other either by printed tracks or by a mounting wire (shown by the dotted line in Fig. 5). For simplicity, only the main radioelements are indicated. The common ground bus of the “top and bottom” of the board should be connected with soldered jumpers at several points along the entire perimeter of the board. The board is mounted on metal stands on a radiator measuring 200x160 mm with fins 25 mm high. Holes are drilled in the board for transistors, and for better thermal contact, the seats for transistors in the radiator are milled and lubricated with heat-conducting paint.

Low-pass filters made according to the data given in Table 1 practically do not need adjustment.

Capacitors must withstand reactive power of at least 200 Var. You can use KSO or CM with a size of at least 10×10 mm. Parallel connection of capacitors of lower power is allowed. Coils of ranges above 10 MHz are wound in increments equal to the diameter of the wire, on low-frequency ones - turn to turn. To switch the low-pass filter, you can use a relay or a roller switch. In the second case, the filter elements must be positioned in such a way as to prevent the signal from “creeping through” the neighboring ones, because their inputs/outputs in this case remain ungrounded.

The matching device circuit can be changed or an additional switch can be introduced to switch different options for switching on the elements. This depends on the design of the antennas used. It is imperative to ensure that the inductance can be changed within small limits, otherwise problems may arise when setting up the matching device in high-frequency ranges.

Fan M1 for blowing the radiator - from the computer power supply. All blocking capacitors are ceramic, of good quality, with leads of a minimum length. Electrolytic capacitors – types K53, K52. Diode VD1 has thermal contact with VT5.

The 24…27 V voltage stabilizer must have a maximum current consumption limitation. We can recommend a circuit that has been used in recent years in transceivers with transistor output stages and has proven itself to be “reliable and simple” (Fig.).

This is a regular parametric stabilizer with short circuit and overcurrent protection. To obtain the required current, parallel connection of two powerful composite transistors with equalizing resistors in the emitter circuit is used.

The output voltage is adjusted by resistor R6, and the current at which the protection is triggered is set by R4 (the higher its resistance, the lower the current). R5 serves to reliably start the stabilizer. At the moment when the output stage is not working and the current consumption of the +24 V source is zero, the voltage at the output of the stabilizer can increase to the input level. To prevent this from happening, a load resistor R7 is included, the value of which depends on the leakage of VT2, VT3 and R5. The assembled stabilizer should be loaded onto a powerful wire resistance and the current at which the protection is triggered should be set. The advantage of this circuit is that the control transistors are attached to the chassis (radiator) without insulating heat-conducting gaskets. When purchasing a KT827A, it is mandatory to check the transistors for leakage, because There are a lot of defects.

Transistor power amplifier winding data.

Matching device (Fig. 1). L1, L2 – frameless, wire diameter 1…1.2 mm, mandrel diameter 16…18 mm, 35 turns each with bends. C10 - from old tube radios, the gap is at least 0.5 mm.

Power amplifier, A1 T1 – “binoculars” (two columns of 4 toroidal cores each, 1000...2000 NM, K7). I – two turns, MPO-0.2 wire; II – 1 turn, wire MPO-0.2.

T2 – “binoculars” (two columns of 5 cores each, 1000NM, K7). 1 – 2 turns of 2 wires MPO-0.2, with a tap from the point of connection of the end of the 1st wire with the beginning of the 2nd; II – 1 turn of braided coaxial cable with a diameter of 3...5 mm (preferably silver-plated), or a copper tube. Winding I is located inside winding II, and its braiding should tightly fit the turns of the first winding.

TZ – one toroidal core, 100...600NM, K16...18. I – 6 turns of 12 twisted wires PEV 0.27...0.31, divided into 2 groups of 6 wires, with a branch from the point of connection of the ends of the wires of the first group with the beginning of the second. II -1 turn of MPO-0.2 wire.

T4 – “binoculars” (two columns of 7 toroidal cores each, 400...1000NN, K14...16. I – a turn of braid from a coaxial cable with a diameter of 5...9 mm or a copper tube. II – 2 turns of twisted 4...5- These wires are MPO-0.2. Winding II is inside I.
L3 – one toroidal core, 1000NM, K10...12, 5 turns of PEV wire 0.4...0.5 mm.
L6 – two toroidal cores, 400...1000NM, K10...12, 8 turns of PEV wire 0.9...1.2 mm or twists of 5...7 PEV wires 0.4...0.5 mm.
L1, L2, L4, L5 – standard chokes type DM, L4, L5 with an inductance of 10...15 µH for a current of at least 0.4 A.

T1 – toroidal core 20…50HF, K16…20. I – a piece of coaxial cable, the braid of which serves as an electrostatic shield and is grounded only on one side. II – 15...20 turns of PEV 0.2...0.4 mm.