Gaz 

Tube FM transmitter.  Diagram of a radio transmitter, walkie-talkie, radio microphone and more in this section. Electrical circuit diagram


We will talk about how to make the simplest and cheapest radio transmitter that anyone who doesn’t even understand anything about electronics can assemble.

Reception of such a radio transmitter occurs on a regular radio receiver (on a landline or in a mobile phone), at a frequency of 90-100 MHz. In our case, it will work as a radio extender for headphones from a TV. The radio transmitter is connected via an audio plug to the TV via a headphone jack.

It can be used for different purposes, for example:
1) wireless headphone extender
2) Radio nanny
3) A bug for eavesdropping and so on.

To make it we will need:
1) Soldering iron
2) Wires
3) Audio plug 3.5 mm
4) Batteries
5) Copper varnished wire
6) Glue (Moment or epoxy) but it may not be needed
7) Old boards from a radio or TV (if any)
8) A piece of simple textolite or thick cardboard

Here is his circuit, it is powered by 3-9 volts


The list of radio parts for the circuit is in the photo; they are very common and finding them will not be difficult. Part AMS1117 is not needed (just ignore it)


The coil should be wound according to the following parameters (7-8 turns with a wire with a diameter of 0.6-1 mm, on a mandrel 5mm, I wound it on a drill 5mm)

The ends of the coil must be cleaned of varnish.


A battery housing was used as a housing for the transmitter.




Everything inside was cleaned. For ease of installation


Next, we take the textolite, cut it and drill a lot of holes (it’s better to drill more holes, it will be easier to assemble)


Now we solder all the components according to the diagram


Take the audio plug


And solder the wires to it, which are shown in the diagram as (input)


Next, place the board in the case (it is most reliable to glue it) and connect the battery




Now we connect our transmitter to the TV. On the FM receiver we find a free frequency (one on which there is no radio station) and tune our transmitter to this wave. This is done by a tuned capacitor. We slowly turn it until we hear sound from the TV on the FM receiver.


Our transmitter is now ready for use. To make it convenient to set up the transmitter, I made a hole in the body

I made this transmitter while still in college. I honestly don’t remember which book the diagram was from, but the book was from the 60s. And the diagram was on some kind of “GU-shka”. But I converted it to 6P14P lamps. If assembled correctly, there is almost no need for configuration. And this type of modulation provides a wide field for experiments. Including a wide frequency range of its operation. In this case, the entire VHF and FM range is covered.

Electrical circuit diagram

  • Power transformer from a tube receiver, 200-250 volts. The rectifier can be made on 226s.
  • Dr1 is also from a 3rd class receiver or TV, it is wound with non-W-shaped iron. 2000 turns of PEL-0.18 wire.
  • Dr2 is wound on a plastic tube, cylinder and contains 40 turns of PEL 0.2 wire.
  • DR3 is the same as DR2 but with a branch from the middle.
  • L1 is two turns of PEL-1 wire, 0.8-1 mm in diameter, and coil L2 is one turn of the same diameter.

And, in fact, adjusting the transmitter - it comes down to bringing these coils closer or further away. But it’s better when one enters the other. I made a transmitting antenna. And I didn’t measure the range exactly. About a few kilometers, I think about five.

While still students, we had fun by generating electromagnetic NE waves and modulated them in amplitude. Naturally illegal. To put it simply, we built it with a friend tube radio transmitters and aired them on NE band. But at that time tube receivers classical folk music has already begun to fade into oblivion prefix – hurdy-gurdy for 6p3s, connected to the sound cascade tube receiver was no longer relevant. That is, not having a tube receiver at home, to go on air, a full-fledged radio transmitter, not a prefix. Semiconductors were in short supply, but radio tubes there were rubble - it was full of dirt all around. And then my friend and I decided to do two tube transmitters- one of which is my copy, is still kept on my mezzanine as a relic and memory of those dark pre-computer times.

Young people then did not have the virtual world and social networks, but only a TV with two channels, a football ground, a bicycle, a tape recorder, and three sevens port wine. Standard set of entertainment of that time. I don't judge whether this is good or bad. It was just like that back then.

Start of construction of the CB transmitter.

In the beginning, in fact, we built and tested one radio transmitter- my copy. The diagram was compiled by us from different parts of different sources and was constantly being reworked to fit the available parts. Parts were obtained from everywhere - exchanged, bought and begged from friends. For example power supply transformer was exchanged, as I remember now, for a new pump from a bicycle from one grandfather. Transmitter It was redesigned several times until it was finally finalized, optimized in terms of the number of parts and structurally designed on a wooden chassis.

CB transmitter antenna.

Transmitter antenna served as a 10-meter wire suspended at a height of about 2 meters on insulators above the roof of a five-story building between two wire radio masts installed on the same roof. That is, the wire was located next to two standard radio broadcast wires, which seemed to mask the antenna. The descent was carried out with an antenna (television) cable, passed into the mast pipe and skillfully carried through the attic of the five-story building and the exhaust shaft directly into the apartment.

CB transmitter parameters.

The transmitter operated at a frequency of about 1000 kHz. All this is of course conditional - according to the receiver’s arrow in the middle of the CB range. I conducted the reception on the radio " Selga 405" - mainly when transmitter testing. After 12 at night he turned on a tape recorder with music connected to transmitter and went out into the street with “Selga” hidden under his jacket. Listening was carried out using one earphone. And so I walked around the city at night, like a special agent on a secret mission - checking the range and quality of reception. My friend sometimes went with the same task, but in his own area - 1 km from me. To control the transmission quality longer - I slowed down the tape recorder motor. So the cassette playing time increased from 30 minutes to 1 hour. We were pleased with the test results. There was a reception in all parts of our area. True, it is much worse on the outskirts. Probably due to not very good antenna. Interference in those days on the NE band it was not enough - not like now, with the massive appearance of switching power supplies and other emitting crap. So basically our transmitter covered the planned area.

The first radio communication on the northeast.

In general, after a series of tests, we then built second transmitter according to the completed sketches and diagrams. It differed from the first one in a 6p15p lamp in the modulator, a power transformer and some design details. Having achieved a coincidence of frequencies - made the first radio communication. We greeted each other on the air and began to take turns yelling like idiots into the microphones, “race - race, race two three, how can you hear the reception.” Scientifically, “adjusting the modulation depth” is called: -). And for some reason, then we didn’t care that we were sitting on the broadcast CB band and in broad daylight we were quacking like fools “all over Ivanovo” from our five-story buildings. Two unafraid idiots :-) . Of course, I wouldn’t allow myself that now. But then, it was cool!

All this fuss with building and testing the transmitter, together with frequent interruptions, took time - probably about a year.

The call sign of my transmitter was “Orion”, the call sign of my friend’s transmitter was “Impulse”. Later we played music after 12 at night. There were no “pro-life” conversations, just like every day as a student at a technical school.

The further fate of the transmitter.

Objectively speaking, at first it was very cool, but over time I quickly got tired of it. Actually myself the process of building a transmitter for the CB range turned out to be much more interesting than playing several dozen tape cassettes on air.

Then my friend went to study in another city, where he stayed. Mine transmitter he bequeathed it to his younger brother, a dunce, who immediately dismantled it into parts along the way. And I played the music a little more and abandoned the matter. But sometimes, I get it from the mezzanine transmitter and like in the good old days, after 12 at night I turn on music for half an hour, inserting the call sign “Orion” into the pauses.

This is a bit of a sad story two tube pirate radio transmitters on the CB broadcast band in one small county town.

Transmitter interference.

Regarding the fact that we could have been “involved” by the relevant authorities: they could! But somehow it went unnoticed. Toli transmitter power is low, perhaps no one complained about interference, or interference They didn't really bother anyone. Another plus is that transmitter master oscillator made not according to the classic Sharman three-point scheme with a bunch of harmonics, but according to the “ GPD Shadsky" - an excellent circuit with a minimum of harmonics ( Radio magazine No. 1, 1963 Page 20). By the way, this is very clearly visible on the computer monitor screen - Receiver SDR. Really, when rebuilding the transmitter only one main peak runs across the range and only pair of harmonic peaks.

Transmitter power amplifier.

The transmitter power could be increased. Later, I had the idea to assemble an amplification stage - attachment on a 6p45 lamp according to the classic single-cycle circuit, but didn’t get around to it. Although, somehow for testing, I soldered with a surface-mounted installation additional stage on another one lamp 6p14p– I liked the result. Transmission range increased significantly. But for some reason it didn’t catch on - I was too lazy to improve this amplifier constructively. Although, in principle, it was possible - there would be room for 6p14p on the chassis.

Circuit diagram of the CB transmitter.

An ULF, also known as a modulator, is assembled on lamp L1, L2. Basically UCH scheme Can be any other lamp.

A master oscillator (GPA) is assembled on lamp L3 smooth range generator) according to Shatsky's scheme. Just a wonderful circuit that produces one clear carrier peak and a couple of weak harmonics at the output. Compared to a three-point generator, it’s “heaven and earth.”

An output signal power amplifier is assembled on lamp L4.

L1 – Generator circuit coil, setting the transmitter frequency. 75-100 turns on the frame from the IF circuit of a USSR TV. The coil is in a standard aluminum screen. *2 standard ferrite cores are screwed into the coil - specifically for this transmitter.

Variable capacitor, connected in parallel L1 – adjustment of the transmitter according to the range (capacitor from transistor radio receiver).

Coil L2 – P circuit. 100 turns (depending on antennas).

Many beginner (and not only) radio amateurs sooner or later become interested in the topic of transmitters. Indeed, the construction of VHF transmitters for the 88-108 MHz range is a fascinating and useful topic. Radio microphones, bugs and other devices can be assembled based on FM radio transmitters. There are many schemes for such devices, but finding a simple, powerful and at the same time stable UHF generator is a problem. After a long search, the choice fell on the following scheme.

The block was built on the basis of well-known circuits, but several modifications were added. The system works almost perfectly, the range is large, and the sound quality is good. BF240 transistors are used, but others can be installed here from the list below. The frequency is changed using a potentiometer.

List of semiconductor elements for assembly

  • BB105G
  • BB104G
  • BF240 (BF199, BF195, BF183,184,185)
  • 2n2369
  • 1n4007

There is only one, very easy to wind, reel. Many people have problems with this, but anyone can wind 5 turns of 1 mm wire on a 5 mm mandrel.

As for shielding, the tin does its job. When tests were done without a screen, the frequency floated and responded to the approach of a hand. After applying the shielding, the circuit worked stably and no longer reacts to the approach of a hand.

Capacitors and power supply chokes can be useful to prevent self-excitation. This did not occur during testing, so the decoupling was not installed.

In addition to the output power level of the radio transmitter, a lot depends on the antenna. You can even receive a signal from it at a distance of up to 1 km if you place a long pin a couple of meters away.

This FM transmitter is built on the basis of a varicap generator and a two-stage power amplifier. With a good antenna - for example a dipole located high enough, the transmitter has a very good range - about a kilometer, maximum range - up to 5 km. The circuit diagram is not at all complicated - with a little experience you can assemble it with your own hands in an evening. A thumbnail image is shown.

Circuit diagram of a powerful broadcast FM radio transmitter

Transmitter PCB Drawings

Radio transmitter specifications

  • - Power: 12-14 V, 100 mA
  • - RF power: 400 MW
  • - Impedance: 50-75 Ohm
  • - Frequency range: 87.5-108 MHz
  • - Modulation: Wideband FM

To adjust for maximum radiation, connect a 6 V / 0.1 A light bulb instead of an antenna. First of all, use resistor R1 to tune to the desired frequency, you can adjust the inductance of coil L1 if necessary. Then use trimmer capacitors C18 and C19 to achieve maximum power (bright lamp light). And only then you can connect the antenna and audio signal to the input of the radio transmitter. Adjust R2 so that the sound is loud enough and high quality, as on other FM radio stations.

The varicap can be replaced with a domestic one, which is installed in SK-V TV modules. For example KV109 or KV104. Transistor BFR96 - KT610. The rest are KT368. Further increase in range is possible with additional .


An FM radio receiver assembled on a single transistor using a regenerative circuit.