master generator.
To achieve frequency stabilization in the control grid, it is necessary to use KSO capacitors of the G + -5% group. The circuit is wound on a frame with a diameter of 20 mm, a wire with a diameter of 0.8 mm 40 turns.

Buffer stage
Everything is clear from the diagram. It can be simplified by removing Dr2 and everything else that goes with it. Put one resistance 27k from the control grid to ground. You can also apply modulation one output of the transformer immediately to the 3rd leg, and remove everything else to ground. The modulator must be a tube modulator and produce 200 volts or more at the output of the modulation transformer, you can use the TC-180 from old tube TVs.


Output stage
Dr1 is wound with a wire of 0.23-0.35 mm on a ceramic frame with a diameter of 10-15 mm, four sections of 80 turns in bulk. Dr2 is wound with three wires on a thick ferite rod (from any receiver where there is a magnetic antenna) incandescent wire 1.0-1.5mm cathode 0.5mm. It is wound up to full filling leaving a place for its fastening. The circuit is wound on a frame with a diameter of 50 mm with a wire of 2.0 mm 35-38 turns. For a more complete calculation of the P-contour, you can use the program: click here


Antenna
Antenna used with this transmitter "American" web length 48m wire 1.6mm reduction 12m wire 1.0mm. The reduction is connected at a distance of 1/3 from the hot end.


But you can use any other antenna you like!

The transmitter consists of the following blocks: master oscillator; buffer cascade; output stage; modulator.

master generator.

The master oscillator is assembled according to the capacitive three-point scheme on a 6P44S lamp. The contour coil is wound on a frame with a diameter of 20 mm, a wire with a diameter of 0.8 mm, 40 turns. To achieve frequency stabilization in the control grid, it is necessary to use KSO capacitors of the G + -5% group.

Buffer stage

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 one, which provides 200 volts and higher at the output of the modulation transformer.

Output stage

Choke Dr1 is wound with a wire of 0.23-0.35 mm on a ceramic frame with a diameter of 10-15 mm, four sections of 80 turns in bulk. The Dr2 inductor is wound with three 0.5 mm wires on a thick ferrite rod. Chokes in the heating circuit are also wound on ferrite rods with a wire of 1.0-1.5 mm. Throttles are wound until the rod is completely filled, leaving room for its fastening. The contour coil is wound on a frame with a diameter of 50 mm with a wire of 2.0 mm, 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 6N2P. The microphone used is an electret (tablet). C1 limits it to high frequencies to avoid excitations. Resistors R1 and R2 determine the voltage at the microphone (affects the 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 the two-stage voltage amplifier. The signal to it comes from the resistance R4 "volume". Resistance R9 is the volume control for the line input (tape recorder, CD player, computer, etc.), it is also the tone control for the microphone input. The sound power amplifier is assembled on 6P3S. The amplifier is loaded on a transformer that you can wind yourself, the data is shown in the diagram. The power transformer from the old TV sets "Record", "Spring" (TS-180) also works well. When connected to a transmitter, it may be necessary to reverse the polarity of the secondary connection.

Antenna

The transmitter was loaded on an American-type antenna. Antenna length 48m from 1.6mm wire. The transmitter was connected with a 1.0 mm wire. The reduction is connected at a distance of 1/3 of the entire length.

The transmitter is based on the C9-1449-1800 synthesizer. At the output of the synthesizer, an oscillatory circuit with a coupling coil and a matching circuit for a wire antenna is installed, in the form of an inclined or horizontal multi-wire beam, 35-55 meters long, raised to a height of 20-30 meters. The output transistors of the synthesizer (KT608B) are powered through an emitter follower on the P701 transistor, which is connected to the 140UD6 operational amplifier in the modulating signal circuit with its base. That is, there is a classic collector modulation with a regulating transistor. The output power of such a transmitter in silent mode is 0.8 watts, when modulated with a sinusoidal signal (telephone power) - 1.2 W, at modulation peaks - up to 3 watts. This is enough to ensure reliable reception within a radius of 1.5 km in urban areas; for rural areas or for settlements with low-rise buildings, the broadcasting radius will already be up to 3 kilometers. That is, it is a transmitter for student campuses, holiday villages and villages, pioneer and student camps, remote military garrisons. It can also be successfully used to demonstrate radio broadcasting to schoolchildren and students in physics and radio engineering classes.

Schematic diagram of a radio transmitter

• drawing of the modulator board and the output oscillatory circuit

However, for all its simplicity, this transmitter fully satisfies the quality indicators for broadcasting transmitters in accordance with GOST R 51742-2001.

The transmitter is powered by a mains rectifier with a power transformer ТН32-127/220-50 and a filter inductor D16-0.08-0.8.

On the front panel of the transmitter are:

• power switch,
• two switches for 4 and 10 positions for setting the nominal frequency of the synthesizer,
• variable capacitor knob for setting the output oscillatory circuit,
• switch of turns of the extension coil (11 positions) of the antenna tuning circuit,
• toggle switch "set-up", switching output power: 40% and 100%.
• blue LED - indicator "Antenna current",
• red LED (lights up in setting mode) - indicator "Output stage current".

On the back panel are:

• mains power connector 220 V, 50 Hz,
• two "tulips" - a linear input of the modulation signal (the adder of stereo channels is inside),
• terminal "Earth", for connection to the ground loop (mandatory!) and to counterweights,
• terminal "Antenna 1" for connecting an antenna, less than a quarter wave long,
• terminal "Antenna 2" for connecting an antenna with a length equal to or greater than a quarter wave.

Transmitter chassis dimensions: 220×110×120 mm.

A schematic diagram of an amateur radio transmitter operating in the medium wave (MW) range with amplitude modulation is given.

As you know, the medium waves of the broadcasting range have already left many radio stations, finally switching to VHF. And there are quite objective reasons for this. So yesterday I turned on the receiver on the MW (MW), and apart from atmospheric noise I heard nothing.

True, in the evening something was barely heard from afar, and in a completely incomprehensible language. And so, our esteemed Federal Communications Agency decided to revive the situation and allocate for individual broadcasting the frequency band 1449-1602 kHz, that is, the “top” of the MW broadcasting range. Which in itself is very reasonable, although a bit late.

On April 24 of this year, the Federal Communications Agency sent information letters on this topic to all interested, in their opinion, persons. Those wishing to study the issue as fully as possible can contact the site cqf.su. All the documentation is there, or links to it.

In short, the essence of the matter is that individual radio broadcasting in the Russian Federation is now officially allowed. You can independently develop, manufacture equipment for individual radio broadcasting, and freely publish these developments in radio engineering literature.

What a radio amateur needs to know who wants to test himself in the matter of individual broadcasting:

1. The frequency range in which the transmitter should operate lies within 1449-1602 kHz. At the same time, the frequency grid in it is in 9 kHz steps. That is, you can calculate 1449 kHz, 1458 kHz, 1467 kHz, etc. Going outside the grid is not allowed and will be penalized.
2. Transmitter power for training and demonstration purposes may not exceed 1 W.
3. Transmitter power for school radio clubs - no more than 25 watts.
4. Transmitter power for centers of children's and teenage technical creativity - up to 50 watts.
5. Transmitter power for technical colleges and technical schools, as well as individual radio broadcasters - up to 100 watts.
6. Transmitter power for technical universities - up to 250 watts.
7. Transmitter power for technical universities and clubs of individual radio broadcasters - up to 500 watts.
8. Type of radiation, - with amplitude modulation, with a band of the modulating signal 50-8000 Hz - 16K0A3EEGN, according to the second volume of the Radio Regulations.
9. Well, now, as it should be, a “fly in the ointment” - you need to register as a media outlet, obtain a license, permission to use the frequency, and commission the equipment. And all this under the same conditions as for professional radio broadcasters. So you understand...

Whatever it was, but "creativity flooded." Well, of course, such a new topic for the application of hands burned with a soldering iron and brains smoked with rosin! And here's what, personally, "knocked out" for me:

Over the long years of the existence of amateur radio, many transmitter circuits have been created and published for operation in the 160-meter range. It will not be difficult at all to move the frequency of such a transmitter to the range of 1449-1602 kHz here.

Accordingly, take measures to stabilize the carrier frequency (in the simplest case, a quartz resonator). It remains to start amplitude modulation, for example, to power the output stage of the power amplifier. Well, practically, the job is done, you can go to the offices to collect papers ...

Schematic diagram of the transmitter

The figure shows a diagram of a simple transmitter, in principle, satisfying the requirements "for training and demonstration purposes".

In practice, this is a slightly modified transmitter by Ya. S. Lapovka (L.1), the frequency of which is shifted to the desired range by replacing the quartz resonator, and by rebuilding the circuit, plus, amplitude modulation is introduced into the output stage.

And now, the transmitter "for training and demonstration purposes" or "pioneer camp" is ready.

Rice. 1. Schematic diagram of an AM transmitter for the broadcast range 1449-1602 kHz.

The Q1 quartz resonator sets the carrier frequency, it must be at the frequency at which it is planned to broadcast, that is, at a frequency in the range of 1449-1602 kHz, taking into account the grid in 9 kHz steps (for example, at 1467 kHz).

Perhaps the quartz resonator in this circuit is the most difficult part to access. However, this problem is being solved. You can purchase a resonator for the closest frequency that differs by a few kHz from the desired one. And adjust by turning on additional capacitance or inductance in series with it.

Not to mention the well-known mechanical methods of fine-tuning the frequency of a quartz resonator.

Amplitude modulation is carried out using a circuit on transistors VTZ and VT4. The VTZ transistor regulates the power supply of the output stage of the transmitter. The LF signal is fed to the VT4 base.

The mode of operation of the modulation circuit is set by a trimmer resistor R6, which regulates the bias voltage based on VT4.

Transmitter details

Coil L1 is a ready-made choke for current up to 2A with an inductance of 10 μH. Coil L2 is wound with wire PEV-2 0.43 on a frame with a diameter of 16 mm and contains 70 turns, winding is carried out "turn to turn". The communication coil L3 is wound over the turns of L2 with the same wire, its number of turns is selected for a specific antenna.

Establishment

When establishing, the operation mode of the cascade on VT1 is set before the installation of a quartz resonator. By selecting R1, a voltage of 5-6V is achieved at its emitter. Then close the collector-emitter VT3 with a jumper, and by selecting the resistance R3 set the quiescent current VT2 at the level of 60-80 mA.

After that, connect the resonator and tune the transmitter for a specific antenna. Remove the jumper from VT3 and adjust the modulator circuit with resistor R6.

In conclusion, I would like to express my personal opinion on this initiative. Of course, to give a piece of the already empty broadcasting range for amateur radio broadcasting is a good idea in itself, although it is twenty years late. Besides, bureaucracy, as usual, can ruin everything.

In my opinion, the same rules should apply here as for amateur radio communications on the HF bands. That is, register the call sign, category (maximum power), and allow broadcasting on any currently free frequency in the range 1449-1602 kHz. Well, maybe, to force them to sign some documents that limit the subject of broadcasting (so that there is no illegal activity).

It would be very interesting to allow private digital broadcasting there as well. Otherwise, the case may dry out in the bud.

Snegirev I. RK-08-16.

Literature:

1. Lapovok Ya. S. Your first transmitter. R-2002-08.
2. cqf.su.

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 for many years lying in boxes. 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 the classical three-point scheme, and despite its simplicity, the frequency keeps stable. The buffer stage on VT2 is loaded on a broadband transformer, it was not a hunt to set the circuit, and then equalize the characteristic over the entire range, there are more brands and details superfluous , and here in one fell swoop, or rather one transformer. The buffer stage is the load of the modulator assembled on the VLF LM386 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 pulled out of some kind of Korean radio. The KT805BM, which was in the first version, did not justify the hopes, and was, with disgrace, dismantled from the transmitter. As a result of the operation, the design was not damaged, but the patriotic spirit of the author was tested. However, having inserted 2T921A into the design for verification, peace of mind was restored. Even more, there was pride in our defense industry. But it was decided to leave the "Korean" as the best option, and it is easier to attach it to the radiator. The operation mode of the cascade is set by resistor R12. Diode D4 serves to stabilize the quiescent current. It must be mounted on a radiator directly near the output transistor. On the Korean transistor, the author slipped the diode directly under the transistor, since there was a place there. It is advisable to coat the attachment point with heat-conducting paste.

Construction details: I installed a variable capacitor with an air dielectric from a tube receiver. You can put almost any KPI, the main thing is to cover 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.
As frames, the author used a polystyrene frame from a spool of thread.
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 over 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 proceeding with the setup, it is necessary to connect the output of the transmitter to a load of 50 - 75 Ohm. The author had two connected parallel 100 ohm resistor, 2 W each.

SETUP:
The setup begins with a power check, after setting the variable resistor R12 to the position of maximum resistance. By connecting an ammeter (multimeter) set to the maximum between the circuit and the power source, usually 10 A, power is supplied. If the readings have not changed much, then you can proceed to the actual setting. Turn off the Tr1 pin that goes to C24 so that power from the modulator does not go to the cascade. Connect a milliammeter between the +24 power supply and the right terminal of the Tr2 transformer. We connect the power, and with the resistor R12 we set the quiescent current of the output stage to about 30 mA. Then we restore all connections, control the signal with a frequency meter or receiver for the presence of generation. Then we set the middle of the range and with capacitors C19 - C21 we set the output filter to the maximum of the indicator readings. We connect the antenna, adjust C21 again and the setup is complete.