Diagram of a radio transmitter, walkie-talkie, radio microphone and more in this section. Homemade fm transmitter

Hello friends. Using this transmitter, you can easily transmit a stereo signal from a smartphone to a car radio with an FM receiver. This stereo transmitter is very easy to manufacture, it is built on one specialized chip BA1404. This chip already includes a stereo audio amplifier, a multiplexer, a subcarrier frequency generator, a carrier frequency generator, and a radio frequency amplifier. The supply voltage of this microcircuit is 1-2V, current consumption is up to 5 mA. Coils L1 and L2 are wound with PEV-2 wire with a diameter of 0.5 mm. on a mandrel with a diameter of 3 mm. and contain 4 turns. The device diagram is shown in Figure 1.

Figure 1 - schematic diagram of a stereo transmitter on BA1404

The device is assembled on one-sided fiberglass laminate measuring 35x50 mm. The printed circuit board is shown in Figure 2.

Figure 2 - printed circuit board of a stereo amplifier based on the BA1404 chip

Radio elements and analogues

Transistor VT1 KT368 can be used with any letter index; transistor KT399 is also suitable

Trimmer capacitor C14 - CTC-05-10RA, ceramic capacitors K10-17 or similar imported ones, for example CL0805.

Resistors are ordinary MLT or similar imported ones.

Setting up and configuring the device

First of all, the transmitter should be tuned to a frequency free from radio stations. Remember that interfering with radio stations is punishable. I advise you to read the Federal Law on Communications No. 126-FZ of July 7, 2003. Circuit C13, C14 and L1 are responsible for the operation of the transmitter at a certain frequency. By adjusting capacitor C14 and increasing or decreasing the distance between the turns of coil L1, we can achieve operation of the transmitter at the frequency we need. Circuit C20, C21 and L2 are responsible for matching the device with the antenna. To adjust the matching, you can use the field strength indicator; if it is not there, then the receiver should be moved away and adjusted by ear, by increasing or decreasing the distance between the turns of the L2 coil. It is advisable to use an antenna with a length equal to a quarter of the wavelength. You can also use smaller antennas, but the communication range will decrease.

References

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We will talk about how to make the simplest and most cheap radio a transmitter that can be assembled by anyone who doesn’t even understand anything about electronics.

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 ends of the coil must be cleaned of varnish.

Reception of the signal from this, the simplest VHF radio transmitter to date, is carried out using a standard (portable, stationary, built-in cell phone), at a frequency of 90-100 megahertz. The circuit is very simple and even for a person who is just starting his amateur radio activities, its assembly will not be difficult.

Radio components and ready-made radio stations with free shipping in this Chinese store.
is returned to you.

It can be used to solve various typical problems, for example:
1) wireless headphones.
2) Electronic nanny for monitoring the baby.
3) Tracking bug.

In the presented version, it will work as a set-top box that will turn regular headphones into wireless ones. The radio transmitter is connected to the headphone jack that your TV has, that is, instead of wires, this simple circuit will now work. This modification can save money by making the device yourself.

For work we will need:
Soldering iron.
Copper wires.
A plug corresponding to the one used to connect headphones to a 3.5 mm TV jack.
Batteries with voltage from 3 to 9 volts.
Copper wire with varnished sheath (will be used for the coil).
Glue Moment if necessary.
Old boards (if possible).
A piece of textolite or thick cardboard.

Simple transmitter circuit

All necessary radio components for the transmitter

The coil needs to be wound 7-8 turns with varnished copper wire with a diameter of 0.6-1 millimeter; on a tube with a diameter of 5 millimeters, for example, you can use a 5) drill. The ends of the wires on the coil must be cleaned of varnish.

For the body of the created transmitter on one transistor, you can use any suitable box. In the example shown, there is a battery container from which all unnecessary partitions and other parts have been removed and removed.

Now let's do it the right size a panel made of PCB and make many holes for the parts. The more of them you get, the more convenient the further assembly and soldering of parts will be.

Now we connect the wires to the plug by soldering in accordance with the diagram (the part that is the input)

On next stage We put the circuit assembled on the board in a box; for reliability, you can secure it with any suitable glue, but this is not necessary. Just make sure that everything is done carefully and during operation of the radio transmitter

All that remains is to configure our transmitter. To do this, use a plug to connect it to the TV. On an FM (VHF) receiver, for example, on a cell phone, we find a free frequency (that is, on which there is no transmission of any radio station) and tune our device to this wave. The frequency is adjusted using a tuning capacitor using a screwdriver. Smoothly rotate it until the sound from the turned on TV appears on the FM receiver.

That's all, you can turn on your headphones mobile phone and watch TV without worrying about noise that might disturb others.

To make adjustments so as not to constantly open the case, make a hole in the transmitter case.

If you replace the audio plug with a microphone, then you will have a radio transmitter that you can put next to the baby and turn on the radio in another room, you will know that the child has woken up, etc. Most likely you will be interested.

FM TRANSMITTER

In just a couple of days I assembled another interesting device"Fm transmitter". The idea of ​​an FM transmitter has been around for a very long time, but somehow we never got around to manufacturing it. The task was to listen to Moscow FM stations, which are broadcast from satellite. In this case, do not drive the TV, but receive it either with a music center or with a mobile phone.

I didn’t think much about the case - it’s a ready-made plastic box, and the price is cheap. The entire structure was covered with a screen made of tinned brass 0.3 mm thick. The screen is simply soldered to the board.

The board is two-sided, installation is entirely on one side, the second is a screen, additionally the negative tracks are soldered to the screen

The FM transmitter circuit represents a conventional capacitive three-point, beep is modulated by a KV109 varicap, and then goes from the generator to the power amplifier. Everything is based on common high-frequency transistors 9018. We wind the chokes on MLT-0.25 resistors, 30-60 turns of 0.1 mm wire.

The size of the FM transmitter board was 30x50mm. Here you can download drawings of boards from the original in the archive.

There were no difficulties in setting up, the transmitter circuit started up immediately. The only thing that was selected were two containers for raising the sound frequency range and a shunt capacitance in the generator to suppress harmonics.

When testing the FM transmitter, I was pleasantly surprised by the performance - the sound was crystal clear, and I was especially pleased with the deep lows. Frankly speaking, the bass turned out to be velvety. At the same time, there are no hints of the background, in short, like a regular FM station, but only in mono mode. The FM transmitter is powered by the receiver itself - it has a 12 volt output at the rear for a tulip-type connector, and in the menu there is an item on/off 12 V. The current consumption of the circuit is approximately 25 mA. Scheme provided by -igRoman-

The simplest radio receivers are not suitable for catching the FM range, frequency modulation. Common people say: this is where the name comes from. From English we interpret the letter FM: frequency modulation. Clearly expressed meaning, it is important for readers to understand: simplest radio receiver FM will not accept it, assembled with your own hands from rubbish. The question of necessity arises: the cell phone picks up the broadcast. IN electronic equipment a similar feature is built in. Far from civilization, people still want to catch broadcasts the old-fashioned way - they almost said with dental crowns - by constructing efficient devices for listening to their favorite programs. For free...

Detector simplest radio receiver: basics

The story touched on dental fillings for a reason. Steel (metal) is capable of converting ethereal waves into current, copying the simplest radio receiver, the jaw begins to vibrate, the bones of the ear detect the signal encrypted on the carrier. At amplitude modulation high frequency repeats the announcer's voice, music, sound in a sweeping manner. The useful signal contains a certain spectrum, which is difficult for a layman to understand; it is important that when adding the components, a certain law of time is obtained, following which the speaker of a simple radio receiver reproduces the broadcast. At the dips, the jaw bone freezes, silence reigns, and the ear hears the peaks. God forbid, of course, you should have a simple radio receiver.

The reverse piezoelectric effect changes the geometric dimensions of the bones according to the law of electromagnetic waves. A promising direction: a human radio receiver.

The Soviet Union was famous for launching a space rocket, ahead of the rest, for scientific research. Union times encouraged degrees. The luminaries have brought a lot of benefit here - designing radios - and earn decent money over the hill. The films promoted the smart, not the wealthy, it is not surprising that the magazines are full of various developments. Series modern lessons creation of simple radio receivers, available on YouTube, is based on magazines published in 1970. Let’s be careful not to deviate from traditions; we will describe our own vision of the situation in the amateur radio industry.

The concept of a personal electronic computer was developed by Soviet engineers. The party leadership recognized the idea as unpromising. Forces are devoted to building giant computing centers. It is too much for a worker to master a personal computer at home. Funny? Today you will encounter more amusing situations. Then they complain - America is shrouded in glory, printing dollars. AMD, Intel - have you heard? Made in USA.

Everyone can make a simple radio receiver with their own hands. An antenna is not needed, there is a good stable broadcast signal. The diode is soldered to the terminals of high-impedance headphones (discard computer ones), all that remains is to ground one end. To be fair, let’s say that the trick will work with the good old Soviet-made D2, the taps are so massive that they will serve as an antenna. We get the earth in the simplest radio receiver by leaning one leg of the radio element against a heating radiator that has been stripped of paint. Otherwise, the decorative layer, being the dielectric of the capacitor formed by the leg and metal of the battery, will change the nature of the operation. Try it.

The authors of the video noticed: there seems to be a signal, represented by an unimaginable jumble of rustles and meaningful sounds. The simplest radio receiver lacks selectivity. Anyone can understand and understand the term. When we set up the receiver, we catch the desired wave. Remember, we discussed the spectrum. The air contains a bunch of waves at the same time, you will catch the one you need by narrowing the search range. There is selectivity in the simplest radio receiver. In practice it is implemented oscillatory circuit. Known from physics lessons, it is formed by two elements:

• Capacitor (capacitance).
• Inductor.

Let's take a moment to study the details; the elements are equipped with reactance. Due to this, waves of different frequencies have unequal attenuation as they pass by. However, there is some resonance. For a capacitor, the reactance in the diagram is directed in one direction, for an inductance - in the other, and the frequency dependence is displayed. Both impedances are subtracted. At a certain frequency, the components equalize, and the reactance of the circuit drops to zero. Resonance sets in. The selected frequency and adjacent harmonics pass through.

The physics course shows the process of choosing the bandwidth of a resonant circuit. Determined by the attenuation level (3 dB below maximum). Let us present the theory, guided by which a person can assemble a simple radio receiver with his own hands. In parallel with the first diode, a second one is added, connected oppositely. It is soldered in series to the headphones. The antenna is separated from the structure by a 100 pF capacitor. Let us note here: the diodes are endowed with pn-junction capacitance, minds apparently calculated the reception conditions, which capacitor is included in the simplest radio receiver endowed with selectivity.

We believe we will slightly deviate from the truth when we say: the range will affect the HF or SV regions. Multiple channels will be received. The simplest radio receiver is a purely passive design, devoid of an energy source; one should not expect great achievements.

A few words about why we discussed remote nooks where radio amateurs crave experiments. In nature, physicists have noticed the phenomena of refraction and diffraction, both of which allow radio waves to deviate from their direct course. Let's call the first rounding obstacles, the horizon moves away, giving way to broadcasting, the second - refraction by the atmosphere.

LW, SW and HF are caught at a considerable distance, the signal will be weak. Therefore, the simplest radio receiver discussed above is a touchstone.

The simplest radio receiver with amplification

In the considered design of the simplest radio receiver, low-impedance headphones cannot be used; the load resistance directly determines the level of transmitted power. Let's first improve the performance using a resonant circuit, then add a battery to a simple radio receiver, creating a low-frequency amplifier:

• The selective circuit consists of a capacitor and inductor. The magazine recommends that the simplest radio receiver include a variable capacitor with an adjustment range of 25 - 150 pF; the inductance must be made according to the instructions. A ferromagnetic rod with a diameter of 8 mm is wound evenly with 120 turns, covering 5 cm of the core. A copper wire coated with varnish insulation with a diameter of 0.25 - 0.3 mm is suitable. We provided readers with the address of the resource where you can calculate the inductance by entering numbers. The audience can independently find, using Yandex, and calculate the number of mH of inductance. The formulas for calculating the resonant frequency are also well known, therefore, while remaining at the screen, you can imagine the tuning channel of a simple radio receiver. The training video suggests making variable coil. It is necessary to push out and push in the core inside the frame with wound turns of wire. The position of the ferrite determines the inductance. Calculate the range using the program; YouTube craftsmen suggest that when winding a coil, draw conclusions every 50 turns. Since there are about 8 taps, we conclude: the total number of revolutions exceeds 400. You change the inductance in steps, and fine-tune the core. Let's add to this: the antenna for the radio receiver is decoupled from the rest of the circuit by a capacitor with a capacity of 51 pF.

• The second point you need to know is that in bipolar transistor There are also p-n junctions, and even two. It’s appropriate to use a collector instead of a diode. As for the emitter junction, it is grounded. Then power is supplied to the collector directly through the headphones DC. The operating point is not selected, so the result is somewhat unexpected; patience will be required until the radio receiver is perfected. The battery also greatly influences the choice. We consider the headphone resistance to be collector resistance, which determines the slope of the transistor's output characteristic. But these are subtleties, for example, the resonant circuit will also have to be rebuilt. Even with a simple diode replacement, let alone the introduction of a transistor. That is why it is recommended to conduct experiments gradually. And the simplest radio receiver without amplification will not work at all for many.

How to make a radio receiver that would allow the use of simple headphones. Connect via a transformer, similar to the one at the subscriber point. A tube radio differs from a semiconductor radio in that in any case it requires power to operate (filament filaments).

Vacuum devices take a long time to reach operating mode. Semiconductors are ready to accept immediately. Don't forget: germanium does not tolerate temperatures above 80 degrees Celsius. If necessary, provide cooling for the structure. At first, this is necessary until you select the size of the radiators. Use fans from personal computer, processor coolers.