A simple circuit of an AM HF transmitter for the amateur 3 MHz band for a novice radio amateur: a detailed description of the operation and device
Proposed transmitter circuit does not contain scarce parts and is easily repeatable for beginning radio amateurs taking their first steps in this exciting, exciting hobby. The transmitter is assembled according to the classical design and has good characteristics. Many, or rather, all radio amateurs begin their journey with just such a transmitter.
It is advisable to start assembling our first radio station with a power supply, the diagram of which is shown in Figure 1:
picture 1:
The power supply transformer can be used from any old tube TV. The alternating voltage on winding II should be about 210 - 250 v, and on windings III and IV 6.3 v each. Since the load current of both the main rectifier and the additional one will flow through diode V1, it must have a maximum permissible rectified current twice as large as the other diodes.
Diodes can be taken of the modern type 10A05 (sample voltage 600V and current 10A) or, even better, with a voltage reserve - 10A10 (sample voltage 1000V, current 10A), when using more powerful lamps in the transmitter power amplifier, we need this reserve It can be useful.
Electrolytic capacitors C1 – 100 µF x 450V, C2, C3 – 30 µF x 1000V. If you don’t have capacitors with an operating voltage of 1000V in your arsenal, then you can make up 2 series-connected capacitors of 100 μF x 450V.
The power supply must be made in a separate housing, this will reduce the overall dimensions of the transmitter, as well as its weight, and in the future it will be possible to use it as a laboratory one, when assembling structures on lamps. Toggle switch S2 is installed on the front panel of the transmitter and is used to turn on the power when the power supply is under the table or on the far shelf, where you really don’t want to reach (can be excluded from the circuit).
Figure 2:
Modulator details:
C1 – 20mkfx300v, C7 – 20mkfx25v, R1 – 150k, R7 – 1.6k, V1 – D814A,
C2 – 120, C8 – 0.01, R2 – 33k, R8 – 1m variable, V2 – D226B,
C3 – 0.1, C9 – 50mkfh25v, R3 – 470k, R9 – 1m, V3 – D226B,
C4 – 100 µFx300V, C10 – 1 µF, R4 – 200k, R10 – 10k,
C5 – 4700, C11 – 470, R5 – 22k, R11 – 180,
C6 – 0.1, R6 – 100k, R12 – 100k – 1m
Electret microphone from a cassette recorder or telephone headset (tablet). The part of the circuit highlighted in red is necessary to power the microphone; if you intend to use only a dynamic microphone, then it can be removed from the design. Trimmer resistor R2 sets the voltage to + 3V. R8 – modulator volume control.
The output transformer is from a tube receiver or a TV of the TVZ type; you can also use vertical scan transformers TVK - 110LM2, for example.
The setting consists of measuring and, if necessary, adjusting the voltages at terminals (1) +60V, (6) +120V, (8) +1.5V of the 6N2P lamp and at terminals (3) +12V, (9) +190V 6P14P.
Figure 3:
Transmitter details.
C1 – 1 section gearbox 12x495, C10 – 0.01, R1 – 68k
C2 – 120, C11 – 2200, R2 – 120k
C3 – 1000, C12 – 6800, R3 – 5.1k
C4 – 1000, C13 – 0.01, R4 – 100k variable
C5 – 0.01, C14 – 0.01, R5 – 5.1k
C6 – 100, C15 – 0.01, R6 – 51
C7 – 0.01, C16 – 470 x 1000V, R7 – 220k variable
C8 – 4700, C17 – 12 x 495, R8 – 51
C9 – 0.01, R9 – 51
R10 – 51
The GPA coil L1 is wound on a frame with a diameter of 15 mm and contains 25 turns of 0.6 mm PEV wire. The inductor in the cathode of lamp L2 is factory-made and has an inductance of 460 μH. In my design, I used a choke from a TV, wound on an MLT - 0.5 resistor with a wire in a slot winding. Chokes L3 - L6 are wound between the cheeks on old-style VS-2 resistors and have 4 sections of 100 turns of PEL-2 wire with a diameter of 0.15 mm. Chokes L7 and L8 each have 4 turns of PEV wire with a diameter of 1 mm wound on top of resistors R8 and R9 MLT-2 with a resistance of 51 Ohms and serve to protect the final stage from self-excitation at high frequencies. The anode choke L9 is wound on a ceramic or fluoroplastic frame with a diameter of 15 - 18 mm and a length of 180 mm. PELSHO wire 0.35 turn to turn and has 200 turns, the last 30 turns in increments of 0.5 - 1 mm.
The L10 contour coil is wound on a ceramic, cardboard or wooden frame with a diameter of 50 mm and has 40 turns of PEL-2 wire with a diameter of 1 mm. When using a wooden frame, it should be well dried and varnished, otherwise, when exposed to high RF current, it will dry out, which will lead to deformation of the winding and possibly even a breakdown between the turns.
C17 is a double unit from a tube receiver with plates removed through one in a movable and fixed block.
Variable resistor R4 sets the bias on the control grid of the 6P15P lamp, and resistor R7 sets the bias for 6P36S lamps.
Relays can be of any type for a voltage of 12V with a gap between contacts of 1mm with a switching current of 5A.
Ammeter for current 100 mA,
The final stage is tuned to resonance using the minimum milliammeter readings.
The bias circuit is shown in Figure 4:
Figure 4:
Transformer T1, any step-down transformer 220v/12v with reverse connection. The secondary (step-down) winding is included in the filament circuit of the lamps, and the primary serves as a step-up winding. The output of the rectifier is about -120V and is used to set the bias of the lamps of the final stage of the transmitter.
Useful thing!
The figure above shows a diagram of the field strength indicator. This is a circuit of the simplest detector receiver, only instead of headphones, it has a microammeter, by which we can visually observe the signal level when tuning the transmitter to resonance.
The transmitter consists of the following blocks: master oscillator; buffer stage; output stage; modulator.
Master oscillator.
The master oscillator is assembled according to a capacitive three-point circuit using a 6P44S lamp. The contour coil is wound on a frame with a diameter of 20 mm, with a wire of 0.8 mm diameter, 40 turns. To achieve frequency stabilization in the control grid, it is necessary to use KSO capacitors of group G + -5%.
Buffer cascade
The buffer stage is designed to decouple the master oscillator from subsequent stages, which contributes to the stability of the generation frequency. In the same cascade, amplitude modulation of the carrier frequency occurs. The modulator must be a tube modulator that provides 200 volts or more at the output of the modulation transformer. 
Output stage
The Dr1 inductor is wound with 0.23-0.35 mm wire on a ceramic frame with a diameter of 10-15 mm, four sections of 80 turns per pile. Choke Dr2 is wound with three 0.5 mm wires on a thick ferrite rod. The chokes in the filament circuit are also wound on ferrite rods with 1.0-1.5 mm wire. The chokes are wound until the rod is completely filled, leaving room for its attachment. The contour coil is wound on a frame with a diameter of 50 mm with a 2.0 mm wire, the number of turns is 35-38
Modulator for AM transmitter
The modulator is a 4-stage low frequency amplifier. The microphone amplifier is made on one half of the 6N2P. The microphone used is an electret (tablet). C1 limits it at high frequencies to avoid excitation. Resistances R1 and R2 determine the voltage on the microphone (affects sensitivity); it should be within 1.5...3.0 V (depending on the type of microphone). Capacitor C3 prevents high DC voltage from reaching subsequent stages. Next comes a two-stage voltage amplifier. The signal comes to it from resistance R4 “volume”. Resistor R9 is a volume control for the line input (tape recorder, CD player, computer, etc.), and it is also a tone control for the microphone input. The audio power amplifier is assembled on a 6P3S. The amplifier is loaded onto a transformer, which you can wind yourself, the data is shown in the diagram. The power transformer from old Record and Vesna TVs (TS-180) also works well. When connecting to a transmitter, you may need to change the polarity of the secondary winding connection.
Antenna
The transmitter was loaded onto an "American" type antenna. Antenna length 48m made of 1.6mm wire. The transmitter was connected with a 1.0mm wire. The reduction is connected at a distance of 1/3 of the entire length.
Class D tube modulator: allows you to increase the efficiency of the radio transmitter in AM mode to 85-90%.Fig.1
The modulating signal Uin is supplied to the input of the PWM signal shaper, which generates voltage pulses on the control grid, the duration of which is proportional to the magnitude of the modulating signal. Accordingly, the voltage on the anode L1 also has the form of PWM pulses. The component of this voltage, varying in accordance with the modulating signal, is isolated by a low-pass filter consisting of (Dr and C). Fig.1
The calculation shows the nominal output power of the radio transmitter in a single-cycle class D modulator on a GU-81m tetrode with 200 watts. up to 600W with a slight decrease in modulator efficiency (from 95 to 85%). In this case, the power dissipated on the shielding mesh will not exceed the permissible level (0.4 kW), and the increasing power losses at the anode will be several times less than the permissible value (600 W).
In order to increase the efficiency in push-pull anode modulators, instead of a class B amplifier, a class D modulator can be used.
Unlike a single-acting amplifier, a push-pull amplifier operates with a duty cycle of two pulses (periods of initial oscillations); there is no voltage at the output of the modulator, since the total average value of these pulses is zero. The voltage, audio frequency Usv.h (Fig. 3) from the PWM unit (Fig. 2) is converted into two sequences of width-modulated pulses G1 and G2 of opposite polarity with a duty cycle of the pulses equal to two initial cycles of oscillations (Fig. 3) for lamps L1 and L2 operating in key mode.
Encoded audio pulses from the PWM modulator are fed to the input of the optocoupler 6N137. At the output of 6N137: the signal is inverted. Therefore, two additional buffer inverting elements D1.1 and D1.3 are used. - (D1-74HC14) inverting Schmitt triggers. (Fig. 4) The signal for the lower key is inverted by inverter D1.2. The control signals of the upper and lower keys are sent to the dead-time generation nodes. They are made on logical elements “AND” D2.1 and D2.2. - (D2-74HC08) . As a result, only the leading edges of incoming pulses are delayed. The amount of delays and, therefore, dead-time is determined by the products of R3*C3 and R4*C4 and can be adjusted to the parameters of the power module. Further processing of the control signals of the upper and lower keys occurs in different ways:
The lower key signal is amplified on the MAX4420 chip and goes to the driver output.
The upper key signal is amplified on the MAX4420 chip and has a “floating” common wire potential. Therefore, galvanic isolation is necessary. In this case, transformer isolation with DC component correction is used.
For a frequency range of 100-300 kHz and a duty cycle from 0 to 0.5, this solution is quite satisfactory.
Transformer parameters: T1 (core M 2500 NMS 16*10*8) winding 2*13 vit. These values are focused on the frequency range 100-300 kHz. If it is necessary to operate at lower frequencies, the number of turns must be increased, and at higher frequencies the number of turns must be reduced. Installation of the half-bridge driver in Fig. 5
Rice. 5 layout option and driver design.
Fig.3
Figure 3 shows the diagram: an alternating component (audio frequency voltage) is supplied to the load through a separating Cp and a constant component through a modulation choke Lg. In order to prevent current interruptions through the inductance Lf when switching lamps L1 and L2, diodes D1 and D2 and shunt lamps are used L1 and L2 and passing currents ivD1 and ivD2 at the required time intervals. In accordance with the direction of the current in the load and in the inductor, only L1 and D2 work in the positive half-cycle of the amplified voltage, and in the negative half-cycle, L2 and D1.
There is no voltage at the modulator output, since the total average value of these pulses is zero. Dependences of changes in the values of average currents through lamps and diodes, related to the peak value. Dependence of the power supplied by a push-pull modulator to the output stage of the transmitter on the AM coefficient, dependence and obtaining efficiency.
Anode modulators for broadcasting transmitters up to 500 kW are built using the sloping principle. Developed by Marconi.
Increasing the efficiency of high-power radio transmitting devices / Ed. A. D. Artyma: Communication 1987.
Foreign radio transmitting devices / Ed. G. A. Zeitlenka, A. E. Ryzhkova - M.: Radio and Communications, 1989.
US Patent N 4272737, class. H 03 F 3/217, 1981.
The transmitter of the second category is designed for half-duplex telegraph communication on the ranges of 10, 20, 40, 80 m and simplex telephone communication on the ranges of 10 and 80 m. The power supplied to the anode circuit of the output stage is 40 watts.
The schematic diagram of the transmitter is shown in the figure in the text.
The transmitter consists of four stages of the high-frequency path (master oscillator, multiplier buffer, doubler amplifier, final amplifier), modulator and rectifiers.
The master oscillator, assembled on lamp L3, operates in the range of 80 m. To increase frequency stability, the screen grid voltage is stabilized using a zener diode L2, and capacitors C20, C24 and C27 with different temperature coefficients are included in the oscillatory circuit of the generator. The frequency of the master oscillator is set by the first section of the dual variable capacitor C21a.
The transmitter is manipulated through the control grid circuit of the master oscillator lamp: when the key is released, a blocking voltage of 75 V is applied to the lamp grid through resistors R26, L25. When the key is pressed, a zero potential is applied to the grid through resistor R25, the lamp is unlocked and the generator is excited.
The excitation voltage for the next stage is removed from the inductor Dr2 through the transition capacitor C38; this stage is made on the L4 lamp and operates in buffer-amplifier mode when operating on the 40 and 80 m ranges and in the buffer-multiplier mode when operating on the 20 and 10 m ranges. In the first case, the inductor Dr4 is connected by relay contacts P1/1 to the lamp anode in series with the L2C34C35 circuit. On the 40 and 80 m ranges the circuit turns out to be detuned, and the role of the input load is performed by the choke. When operating on the 20 and 10 m ranges, relay P1 switches inductor Dr4 into the lamp anode power decoupling circuit. In this case, the 4th harmonic (20 m) of the master oscillator is allocated on the L2C34C35 circuit. To better isolate this harmonic, the circuit is adjusted with capacitor S21b (the second section of the block of variable capacitors) simultaneously with setting the frequency of the master oscillator.
The third stage is made on an L5 lamp, which operates, depending on the range, either in amplification mode or in doubling mode. On each band, a separate circuit is connected to the anode of the lamp using switch P3: on the 80 m range - circuit L3C42, while the lamp operates in the oscillation amplification mode; on the 40 m range - circuit C4C43 the lamp operates in doubling mode; on the 20 m range - L5C44 circuit, the lamp operates in amplification mode; on the 10 m range - L6C45 circuit, the lamp operates in doubling mode. Using capacitor C46, each circuit is adjusted to obtain the required excitation voltage of the final stage, which is especially necessary when operating on the 20 and 10 m ranges. Negative bias is supplied to the control grid of lamp L5 from a voltage divider on resistors R46, R47.
From the anode of lamp L5, the excitation voltage through capacitor C48 is supplied to the grid of lamp L6 of the output amplifier, which operates in power amplification mode on all ranges. The anode load of this cascade is a P-circuit, consisting of coils L7 L5 and capacitors C55, C57. The coils are switched when moving from one range to another using relays P2 and P3. An electronic antenna switch is assembled on diodes D22 and D23, the use of which allows you to use the same antenna for the receiver and transmitter and operate in half duplex. A stabilized bias voltage is supplied to the control grid of lamp L6 through inductor Dr7 from gas-discharge stabilizer L1.
The modulator is assembled on transistors T1, T2 and lamp L7. It is designed to work as a dynamic microphone. The sensitivity of the modulator is no worse than 2 mV with uneven frequency response in the frequency band 300-3,000 Hz + 3 dB. Above 3,000 Hz, the modulator's frequency response drops sharply, resulting in a narrow emission bandwidth. The modulation depth is regulated by a variable resistor R34, on the axis of which the modulator switch Bk2 is installed. The transition from telegraph to telephone mode is carried out using switch P1. Modulation - on the pentode grid of the final stage.
To configure and control the operating mode of the transmitter, the IP1 device is provided. Using switch P4, it is connected either to the grid or to the anode circuit of the output stage lamp. In the first case, the device measures current up to 15 mA, in the second - up to 150 mA.
The transition from range to range is carried out with one handle - switch P3, with the help of which all the necessary switching of the relays and circuits of the pre-terminal stage is carried out.
To avoid radiation when tuning the transmitter to the correspondent frequency, the output amplifier is switched off at these moments using switch P2.
The transmitter is powered by four rectifiers. The anode voltage of 600V for the output lamp is removed from two series-connected rectifiers assembled on diodes D1-D16. In the 600 V voltage circuit, filter C2R9C3 is included. To power the anode and screen circuits of the remaining lamps, a rectifier based on D9-D16 diodes with filter C4, Dr1, C5 is used. A half-wave rectifier based on diode D17 with filter C6, R21, C7 is used to obtain bias voltage. A 24 V rectifier on diodes D18-D21 with a filter capacitor C8 serves to power the modulator and relay.
Details. The power transformer Tr1, choke Dr1, loop coils and high-frequency chokes of the transmitter are homemade. The transformer is assembled on a Sh-25 core, the thickness of the package is 50 mm. Winding data is given in table. 1.
| Winding | Number of turns | The wire |
| 1 | 935 | PEV 0.51 |
| 2 | 1050 | PEV 0.25 |
| III | 960 | PEV 0.41 |
| IV | 500 | PEB 0.15 |
| V | 85 | PEV 0.35 |
| VI | 54 | PEB 0,8 |
| VII | 28 | PEV 1.0 |
The Dr1 throttle is made on a Sh-15 core, the thickness of the package is 32 mm. It contains 1250 turns of PEV 0.38 wire.
Data for loop coils and high-frequency chokes are given in table. 2.
| Designation | Frame | |||||
| Number of turns | The wire | material | diameter, mm | Winding | Inductance, μgn | |
| L1 | 32 | palsho 0.51 | polystyrene | 18 | solid, one layer | 10 |
| L2 | 10 | PEV 1.0 | » | » | » | 1,5 |
| L3 | 46 | PEV 0.7 | » | » | » | 14 |
| L4 | 19 | PEV 1.0 | » | » | » | 4 |
| L5 | 10 | » | » | » | » | 1,5 |
| L6 | 4 | silver plated 2.9 | without frame | 20 | step 2 mm | 0.3 |
| L7 | 22 | » | » | 33 | step 1 mm | 5 |
| L8 | 7 | » | » | 35 | pitch 3 mm | 1,4 |
| DR2-DR8 | 200×4 | PELSHO 0.15 | textolite | 5 | station wagon | 3000 |
All fixed resistors are MLT type. You can use other resistors of appropriate resistance and power. Capacitors C2-C9, C13, C15, C18 - electrolytic; C1 type KBGI, KBGM with an operating voltage of at least 400 V; C10, C14 C16 – MBM type; S11, C12, S19, S39, S41, S49, S51, type BM-2; C17, C23, C28, C37, C38, C48, C56 - KSO type (C23 - preferably group G; C20, C24, C27, C35, C36, C42, C42, C44, C47, C58 - KT type C24 blue, C27 - Red); S25, S30, S32, S33, S40, S50 - type K40P; C53, C54 - SGM type; S22, S34 - type KPK-1; C21, C57 - standard twin units of any type; in C57, the fixed plates of both sections are connected in parallel; C46 - any type, this design uses KPV-140 with an extended axis; C55 - any type, with a gap between the plates of at least 0.8 mm, this design uses an antenna capacitor from the R-104 radio station.
Switches P1, P2, P4 toggle switches TP1-2, P3 - two-bar type 4P4N. Relay R1-type RES-6 (passport RF0.452.141) or RES-9 (passport RS4.524.201). P2, P3 - high-frequency of any type, for example from the RSB-5 radio station.
Measuring device - type M4203 with a scale of 15 mA or any other with the same total deflection current. Instead of one device, you can install two - in the grid and anode circuits - instead of resistors R48 and R51. In this case, switch P4 and resistors R48, R51, R52 are not needed.
Some kind of vernier should be installed on the axis of the capacitor unit C21. Scale - any type. In the design described, it is made on organic glass and illuminated from behind (with lamps JI8 and L9). A pointer is mounted on the vernier axis.
Zener diodes SG1P and SG16P can be replaced with SG4S and SG2S, respectively, transistors MP41 - with MP39 - MP42.
The design of the transmitter is shown on the 1st page of the tab. The transmitter is mounted on a horizontal chassis with dimensions 400X230X65 mm. The front panel with dimensions 400 X X 170 X 2 mm is fastened to the chassis with bolts and brackets. This makes it possible to install the transmitter in any position, which is convenient during assembly and installation. The cascades are separated from each other by partitions. The chassis, front panel and partitions are made of duralumin. The transmitter is placed in a detachable casing with holes for heat dissipation.
The rectifier elements, as well as resistors R18-R24, R40, R42, R44, R49, R50, R53, are mounted on two printed circuit boards, each of which is mounted on a power transformer (bottom and top). Most of the modulator elements are also mounted on a printed circuit board.
Methods for tuning transmitters were repeatedly described in detail in the Radio magazine, for example, in No. 10 for 1967 and No. 1 for 1968. All of them fully apply to this transmitter. It is only necessary to note the following. After checking the operation of the rectifiers, the master oscillator should be adjusted using the GIR or a precisely calibrated receiver. In this case, switch P2 should be in the “setup” position, P1 - in the telephone position.
The required frequency range of the master oscillator is set roughly by selecting the capacitance of capacitor C20 and precisely - C22. Then, by adjusting the capacitance of capacitor C34 and bending the plates of section C21b, circuit L2C34C35 is adjusted.
The third stage is adjusted according to the maximum reading of the IP1 device, connected to the grid circuit of lamp L6 with frequency control at the receiver or GIR. It is necessary to ensure that each circuit is tuned with capacitor C46 at the beginning, middle and end of its operating range. In this case, the device readings on the ranges of 80 and 40 m should reach 15 mA, on 10 and 20 m - 10-15 mA.
The output stage is tuned to the equivalent of an antenna (a resistor with a resistance equal to the characteristic impedance of the feeder and a power of at least 30 W, or an incandescent lamp). When switching to telephone mode, the anode current should drop by half compared to the telegraph mode.
AM TRANSMITTER at 3 MHz
The transmitter consists of four stages. The author used almost all used parts, soldered at different timesfrom different techniques, and lay around in boxes for many years. The output power of the transmitter has not been measured, according to rough calculations it is about 5 Watts +/-, but most likely a plus. The master oscillator is assembled according to a classic three-point circuit, and despite its simplicity, it maintains a stable frequency. The buffer stage on VT2 is loaded on a broadband transformer, there was no desire to install circuits and then equalize the characteristic over the entire range, there are more brands and details extra , and here in one fell swoop, or rather with one transformer. The buffer stage is the load of a modulator assembled on an LM386 ULF chip. The author took the modulator circuit from Japanese radio amateurs, tested it and was satisfied. Well, the most important part is the final stage. It is assembled on a transistor taken from some Korean radio. The KT805BM in the first version did not live up to expectations and was disgracefully removed from the transmitter. As a result of the operation, the structure was not damaged, but the patriotic spirit of the author was tested. However, having inserted 2T921A into the design for testing, peace of mind was restored. Even more, there was pride in our defense industry. But it was decided to leave the “Korean” as the most optimal option, and it is easier to attach to the radiator. The operating mode of the cascade is set by resistor R12. Diode D4 serves to stabilize the quiescent current. It must be mounted on the radiator directly next to the output transistor. On the Korean transistor, the author slipped a diode directly under the transistor, since there was room there. It is advisable to coat the mounting location with heat-conducting paste.
Design details: a variable capacitor was installed with an air dielectric from a tube receiver. You can install almost any KPI, the main thing is that it covers the range of 2.8 - 3.2 MHz.
Coil L1 of the master oscillator has 80 turns of PEL wire - 0.32 with a tap from 20 turns. Coils L2; L3 are the same and have 20 turns of PEL wire - 0.6.
All coils are wound on frames with a diameter of 12 mm.
The author used a polystyrene frame from a spool of thread as frames.
Tr1 is wound on a ferrite ring with a diameter of 10 mm and a height of 5 mm. Twenty turns of folded and slightly twisted PELSHO wire - 0.25. Winding is carried out evenly throughout the entire ring.
Tr2 is wound on the same ring and contains 18 turns of PEL wire folded in three - 0.32.
L4 - 30 turns PELSHO - 0.25 on the same ring as Tr 1;2. For L4, you can use a ring with smaller dimensions.
ATTENTION:
Before you start setting up, you need to connect a 50 - 75 Ohm load to the transmitter output. The author used two connected parallel 100 Ohm resistors, 2 W each.
SETUP:
The setup begins by checking the power supply, having previously set the variable resistor R12 to the position of maximum resistance. By connecting an ammeter (multimeter) set to maximum between the circuit and the power source, usually 10 A supplies power. If the readings have not changed much, then you can proceed to the actual setup. Disconnect pin Tr1, which goes to C24 so that power from the modulator does not flow to the cascade. Connect a milliammeter between power supply +24 and the right terminal of transformer Tr2. We connect the power, and with resistor R12 we set the quiescent current of the output stage to about 30 mA. Then we restore all connections, monitor the signal with a frequency meter or receiver for generation. Then we set the middle of the range and use capacitors C19 - C21 to adjust the output filter to the maximum indicator readings. We connect the antenna, adjust C21 again and the setup is complete.
