Wideband power amplifier based on RF2113. Transistor power amplifier winding data

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 a system automatic adjustment output power).

The broadband INA50311 (Fig. 33.13), manufactured by Hewlett Packard, is intended for use in mobile communications equipment, as well as in household electronic equipment, for example, as 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.

This amplifier on one chip can be used in various electronic devices. This could be an amplifier for a radio station, radiotelephone, radio microphone, bug...

The microcircuit is available in 8-pin plastic case SOIC. The device is autonomous, with the exception of the output matching circuit, power supply line and blocking capacitors.

The single-pack amplifier is manufactured using an advanced Gallium Arsenide Heterojunction Bipolar Transistor (HBT) process. Designed for use as a final linear RF amplifier in microwave radio transmitters operating in the frequency range from 1 MHz to 1 GHz. It can also be used as preamp for driving a power amplifier.

Circuit diagram for connecting the RF2113 chip for amplification at a frequency of 900 MHz.

The L, R and C ratings are determined for a frequency of 900 MHz. The voltage at pin 5 does not have much effect on the gain.

Characteristics of the RF2113 chip

• Power 1 W, at frequencies up to 450 MHz, 0.5 W at frequencies up to 1 GHz;
• Gain coefficient of at least 31 dB, depending on the output matching circuit;
• Efficiency 42%;
• The power supply is unipolar 2.7 - 7.5 V, when the supply voltage is reduced to 3 V the power is 125 mW.

5 - watt power amplifier for the range 1.8…54 MHz

Zack Lau, KH 6 CP /1. The original article was published in the magazine QEX , May 1992, pp.7,8

You need a simple and stable amplifier for multi-band QRP transmitter? This amplifier has not only been optimized for stability using a computer program Touchstone , but also withstood the connection to it during operation of various kinds of unmatched (high-resistance) loads, for example, the RA was used to measure the characteristics of filters with an output power of 5 W. Gain of two-stage RA within amateur bands is 28...30 dB and has a slight rise of a couple of dB at frequencies near 37 MHz. For the simplicity and unpretentiousness of the RA, its terminal transistor was chosen MRF 137 from Motorola. With MRF The 138 amplifier may be more linear, but I have very little information on this transistor to be completely confident in it. Some radio amateurs are put off by the increased cost of these transistors, but, as they say: “the miser pays twice,” cheap transistors tend to “fail” often. An amplifier with field-effect transistors produces a “clean” output SSB a signal comparable in terms of high-order intermodulation products to conventional bipolar transistor amplifiers. For example, the worst-case intermodulation product level for the 3.5, 7, 14 and 28 MHz bands is -38 dB at 28 MHz, with fifth-order products having a level of -61 dB relative to PEP. The amplifier has output power 5 W PEP at a current of 0.5 A (supply voltage 28 V).

Probably the biggest drawback is the peculiar nutrition field effect transistors- they “love” high voltage and, at the same time, work really well. MRF 137 is no exception. I fed MRF 137 with a voltage of 28.2 V at a quiescent current of 0.55 A. The current increased to 0.6 A with an output power of 4.6 W at 28 MHz. The driver was supplied with the usual, in such cases, supply voltage of 12 V.

The input stage of the amplifier (Fig. 1a) is made on bipolar transistor 2 N 5109 with feedback adjusted to compensate for gain MRF 137. A series circuit consisting of a 470 Ohm resistor and a 12 pF capacitor is installed between the collector and the common wire to ensure the stability of the amplifier at all its operating frequencies. MRF 137 at 54 MHz already reduces its own gain by several dB, however, this difference is compensated by the bipolar transistor amplifier. Input return loss is better than 18 dB from 1.4 to 29.9 MHz, but degrades to 12 dB at 50 MHz. Input SWR with high-resistance loads was not checked.

The final power amplifier stage “in person” is shown in Fig. 1 b and is an excellent amplifier unit with a gain of 16 dB and gain flatness of less than 0.5 dB in the frequency range 1...32 MHz. A transformer on the transmission line connected to the amplifier input allows improving return losses and SWR, which are, respectively, more than 18 dB and 1.3: 1 in the frequency range 1...50 MHz. I think that connecting another transformer on the transmission line at the output of the amplifier will make it possible to create a more powerful PA with less gain for the same frequency range, such a variation, however, has not been tested.

The simplest board I could think of was used for the amplifier. On a piece of fiberglass foil on both sides, I cut out two tracks for the gate and drain terminals, then wrapped the board around the edges with copper foil tape and soldered it for reliable “grounding” (shielding).

Rice. 1a. Low-power amplifier designed to compensate for frequency response rolloff

Power amplifier on MRF 137. Electrical circuit diagram.

Q 1 – 2 N 5109, 2.5 Watt Heatsink Mount Transistor, Boundary

Frequency Ft = 1200 MHz.

T1 – 15 turns of double #28 wire on a ring core FT -37-43.

After drilling holes for the transistor MRF 137, the screws for securing it to the board and to the gasket made of aluminum tape 0.05 inches thick, I attached the gasket, board and transistor to the radiator using 4-40 screws (holes were drilled in the body of the radiator for this purpose and threaded appropriate thread). Standard method, “pressed” to the common wire, was used for mounting other parts. Transistor amplifier 2 N The 5109 is mounted on its own ground plane, and one more thing: if the gain in one stage of an RF amplifier is “jacked up,” then that amplifier operates less stable (i.e., the gain between stages should be distributed more evenly).

Three such amplifiers were built Mike ' o m Gruber ' o m, WA 1 SVF for laboratory use. He noticed that the resistance of the resistor R 8 to obtain the necessary bias to produce a current of 0.5 A must be changed from 4.7 kΩ to 1 kΩ. Additionally: used Mike 'ohm transistors MRF 137 had a higher gate threshold voltage (the bias voltage required to turn on the transistor), but this did not affect the amplifier parameters.

Rice. 1b. MOS power amplifier ( TMOS )-transistor with output power 5

Tue Basic electrical diagram.

L 1 – 26 turns of #26 enameled (winding) wire on a T-44-2 ring,

Inductance – 3.9 µH.

Q 2 – transistor MRF 137.

R 9 – potentiometer (tuning resistor) with a resistance of 10 kOhm

Rotary type to set the transistor bias voltage.

RFC 1 – 21 turns of #26 wrapping wire per ring FR -37-67.

T2 – 4 turns of 25 ohm coaxial cable on a ring FT-50-43. 25 ohm

The cable is formed by two pieces of 50-ohm cable laid

Parallel. The prototype used a cable RG -196/ U .

U 1 - 78 LO 5 – integrated 5-volt stabilizer.

Free translation from English: Victor Besedin (UA9LAQ) [email protected]
Tyumen January, 2003

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. Yet radio amateurs rarely use homemade designs at a power of more than 30-40 W. This, of course, is due to the shortage of 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 various types transistors in silos of transceivers showed their clear advantages in comparison with tube ones at 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.

1. 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.
2. Look at the reference book at least once and carefully read the parameters of the transistor used.
3. None of the maximum permissible parameters must be exceeded.
4. 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.
5. 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.
6. 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.

1. 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. dimensions amplifiers 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 applied simplest option– 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 must 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 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 coil of silver braiding is stretched from coaxial cable, and already inside this braid 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 when 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 biscuit 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 cooling the radiator - from the computer power supply. All blocking capacitors are ceramic, good quality, with leads of minimal 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.

The push-pull power amplifier is intended for use in QRP equipment operating in low-frequency KB bands (1.8-10.1 MHz). It uses inexpensive IRF510 insulated gate field effect transistors. The amplifier was developed by Australian shortwave driver Drew Diamond (VK3XU). A description of the amplifier was published in The Radio Communication Handbook (RSGB). In the ranges of 1.8-7 MHz, the amplifier provides output power of 5 W (OM) and 6 W (SSB, PEP) with an input power of 100 mW. On the 10.1 MHz range, these parameters are provided with an input power of 300 mW. Intermodulation distortion measured on a two-tone signal is no worse than -30 dB relative to the carrier. Suppression of harmonic components in the output signal is no worse than -50 dB relative to the carrier. The amplifier is highly reliable, it is not excited at any load SWR value and can withstand output short-circuiting at full output power. The amplifier circuit is shown in Fig. 1.

Antiphase signals at the gates of field-effect transistors VT1 and VT2 are provided by transformer T1. Negative Feedback through resistors R3 and R4 stabilizes the operation of the amplifier and expands its operating frequency band. The supply voltage is supplied to the drains of the amplifier transistors through the balun transformer T2. The output signal goes to BALUN (transformer TZ) and then to the output through the low-pass filter L1-L3C6-C9. The circuit that sets the bias voltage on the gates of the amplifier transistors includes a zener diode VD1 with a stabilization voltage of 3.3 V. However, its main purpose is not to stabilize the voltage, but to regulate the bias voltage depending on the temperature of the heat sinks of the amplifier transistors. As the temperature rises, the bias voltage decreases, reducing the quiescent current through the transistors. The Zener diode VD1 is installed so that thermal (but not electrical!) contact with the heat sinks is ensured. For this purpose, heat-conducting paste is used. The amplifier supply voltage is 13 V. The initial quiescent current of the transistors is set within 200...300 mA using trimming resistor R2. The current consumed by the amplifier from the power source, with an input power of 100 mW and an equivalent antenna with a resistance of 50 Ohms connected to its output, should be close to 1 A. Correctly sized heat sinks after several minutes of operation should heat up to an acceptable (when touched by hand) temperature. The power amplifier is assembled on printed circuit board made of fiberglass foil 2 mm thick on both sides. The board drawing is shown in Fig. 2.

On one side of the board, mounting pads are cut out, to which the leads of all amplifier elements are soldered. The second side of the board, used as a common wire and screen, is connected to the working side at several points, designated by the letters X. Transformers T1-TZ are wound on ring magnetic cores from Amrdon FT50-43, size 12.7x7.15x4.9, made of ferrite with initial magnetic permeability 850. All windings contain 11 turns of wire with a diameter of 0.5 mm for T1 and a diameter of 0.64 mm for T2 and TZ. The inductance, number of coil turns and capacitance of the output low-pass filter capacitors for various ranges are shown in the table.

Range, MHz	Capacitor capacity, pF		Inductance of coils L1-L3, μH/number of turns
	C6.C9	C7, C8
1,8	1800	3300	4,7/25
3,5	820	1800	2,2/17
	440	820	1,1/12
10,1	220	440	0,55/8

The coils are wound with wire with a diameter of 0.64 mm on ring magnetic cores made of carbonyl iron from Amidon T68-2 with a standard size of 17.5x9.4x4.8. Ferrite magnetic cores are not applicable here, so in the absence of carbonyl iron rings, the coils can be made frameless. In this case, it will apparently be necessary to slightly increase the size of the board in order to place such a low-pass filter on it. Oxide capacitor C5 - tantalum for a rated voltage of at least 25 V The rest are ceramic. If there are no filter capacitors of the required capacity, they can be selected from several. The type of zener diode is not indicated in the original source. The board, the drawing of which is shown in Fig. 2, corresponds to a single-band version of the power amplifier. In a multi-band design, a low-pass filter is installed on the board only for the highest frequency range, and the low-pass filter parts of the remaining ranges are mounted separately with the corresponding switching elements

Radio No. 3 2011 p. 58