Circuit of a simple walkie-talkie with 2 transistors. Scheme of a homemade walkie-talkie

Modern element base allows you to create radio-electronic devices with excellent technical characteristics, minimal size and low power consumption.

Of course, for radio amateurs living far from large cities and regional centers, the possibility of purchasing foreign integrated circuits is practically unrealistic, even though they are relatively inexpensive. However, this does not mean that the design of devices using modern ICs should be stopped.

Radio amateurs are offered the option of a portable radio station, very similar to the “Hummingbird” radio station. Compared to the “Hummingbird”, the described design has higher value output power, better sensitivity of the noise reduction system (SNR), and also uses a slightly different connection of the IC and transmitter transistors.

Specifications

• receiver sensitivity, no worse, µV...................0.5;
• transmitter output power, W...................................3;
• deviation, kHz................................................... ...............3;
• type of modulation................................................ ............ World Cup;
• communication range in open areas, km...................................6;
• communication range in city conditions, km...................................2.

It should, however, be noted that the characteristics of the radio station depend on many factors, therefore, when repeating the design, deviations of the values ​​​​up or down from those indicated above are possible.

Schematic diagram

In Fig. 1 shows the principle electrical diagram radio stations. In transmission mode, the signal from the VM1 microphone is supplied to the cascades of the DA1 MC2833R transmitter microcircuit. IC DA1 performs the functions of amplifying the low-frequency signal, limiting it, generating a high-frequency signal and modulating it.

The microcircuit also includes two transistors capable of operating at frequencies up to 200 MHz (according to the datasheet - up to 500 MHz). The signal from the RF amplifier (pin 14 DA1) is supplied to the base of the first transistor (pin 13) through the resonant circuit L2, NW, on which the main signal of the transmitter is isolated (or a harmonic if a quartz resonator is used at a minor frequency).

In the collector circuit (pin 11) a resonant circuit L3, C8 is installed, tuned to the transmission frequency. From the coupling coil L4 through the separating capacitor C10, the modulated signal of the operating frequency is supplied to a line of amplification stages on transistors VT1., VT2 and then through a double P-circuit to the antenna WA1.

Rice. 1. Schematic diagram homemade radio station at 27 MHz, 3 Watt capacity.

In reception mode, the signal from antenna WA1 through capacitor C27 is supplied to communication coil L12. Now the second transistor of the DA1 chip performs the function of a resonant UHF receiver. Using a bipolar transistor as a UHF, of course, cannot be considered the optimal solution. It would be better to use a field-effect transistor (for example, KP307, KP350).

However, when developing the radio station, the goal was to create a design with the least number of parts, overall dimensions and cost. For those who like experimenting, we can recommend using the second transistor IC MC2833 as part of the transmitting path, and using a field-effect transistor as a UHF receiver.

Next, the received signal is fed to the DA3 multifunctional chip, where the high-frequency signal with frequency modulation is completely converted into a low-frequency information signal. This IC contains an adjustable noise suppression system. From output DA3 (pin 9), through the volume control resistor R15, the low-frequency signal is supplied to the ULF, made on the DA2 MC34119R IC.

Switch SA2 turns off the standby mode in cases where the signal from the received radio station is at a very low level. Transistors VTZ and VT4 are used as an SNR amplifier.

When a received signal appears, the noise level decreases significantly and the transistors put the DA3 chip into working condition. The rest of the time, this IC is in the “off” state. This allows you to significantly reduce energy consumption during duty reception.

The microcircuits are powered using integrated stabilizers DA4, DA5 78L06, so the functionality of the radio station is maintained when the supply voltage is reduced to 6...7 V. Instead of the indicated ICs, stabilizers of the 78L05 type can also be used, but in this case the output transistors of the transmitter will operate with low efficiency , not providing communication over the proper distance.

One of the disadvantages of this design can be considered the need to select receiver and transmitter crystals with an IF difference (usually 465 kHz, but 455 kHz is also possible). However, this gives a gain in the size of the device as a whole and improves frequency stability.

Even a beginner can set up a radio station. However, the radio station should be assembled in stages. That is, they install the elements of those cascades that will be configured at the current time. This will avoid many problems in setting up the entire device. First, the operation of the receiver is checked, and then the transmitter.

Assembly and configuration procedure

1. Receiver:

• a) ULF chip DA2 and corresponding attachments up to resistor R15 of the volume control;
• b) DA3 receiver chip and corresponding attachments up to UHF; in this case, the SPS should be turned off by closing contacts SA2;
• c) setting up the IF circuit L15, C42.

2. Transmitter:

• a) transmitter chip DA1 and corresponding attachments to transistor VT1;
• b) setting up the L2, SZ and L3, C8 circuits into resonance (at this stage you can separate the receiver and transmitter by a distance of 3...5 m and adjust the IF circuit);
• c) line of transmitter transistors VT1 and VT2 and P-circuit elements (L7, L8, C16...C18).

It should be remembered that the transmitter power amplifier must be configured with an antenna or its equivalent connected! First we set up the L5, C11 circuit, and then the P-circuit. As a result, we adjust all the transmitter circuits (if necessary) until the maximum performance of the device used is achieved and we tune the UHF receiver circuits L11, C26 and L14, C28 into resonance. Now you can adjust the SNR using variable resistor R23 based on the received signal from the transmitter.

In both modes (reception and transmission), it will be necessary to tune the RF circuits to resonance. By changing the inductance of coil L1, it is necessary to set the operating frequency (according to the receiver). Resistor R9 regulates the gain of the microphone amplifier. The greater the resistance of R9, the greater the gain. In the receiving mode, you should configure the IF circuit according to the received signal (or preset it to maximum level noise with the PN system turned off; and finally - according to the received signal). Then the UHF input circuits are adjusted.

Finally, the P-circuit is adjusted to the maximum current in the antenna in transmit mode. It is better to make adjustments using a non-resonant wave meter based on the maximum deflection of the instrument needle. The antenna can be used either telescopic or spiral. It all depends on the “taste” of the designer. You should definitely remember that without an antenna or if its connection is poor, you can damage the output transistor of the transmitter power amplifier, so its installation must be taken with full responsibility.

The SPS switch SA2 should be connected not between the base of the VTZ transistor and the common wire, but between the VTZ base and the right (according to the diagram) output of the DA5 stabilizer through a resistor with a resistance of 68 kOhm.

When contacts SA2 are closed, the operating point of the transistor VTZ shifts, which turns off the system and allows you to listen to weak signals under poor reception conditions.

To adjust the SSH response threshold, it is necessary to temporarily install a variable resistor with a resistance of 27 kOhm instead of resistor R22. The resistor R23 slider is placed in the middle position and, by rotating the temporary resistor slider, a position is found in which the SNR switches in the absence of a transmitter signal. Then, having measured the resistance of the temporary resistor, a permanent resistor is soldered in its place.

Details and finalization of the scheme

The transmitter power amplifier has been improved. To do this, the values ​​of resistors R5 and R7 were changed to 1 kOhm each, and resistors R* 33 kOhm and R** 47 kOhm were added (Fig. 2). Since in this case the operation of the power amplifier stages occurs in class A, the quiescent current of the transistors increases. However, in this case there is a noticeable increase in the gain and, accordingly, the signal sent to the antenna, which in turn increases the communication range.

Rice. 2. Refinement of the transmitter power amplifier, circuit.

The winding data of the inductors are given in table. 1.

Chokes L6, L9, L10 are standard type D-0.1 with an inductance of 110 μH. The coil of the IF circuit is wound on an SB-12 core. The adjustment is made by rotating the core. Frameless coils L7, L8 P-circuit are adjusted by stretching or compressing the turns.

If you couldn’t find the MC34119R chip, don’t despair. The silent setting function can be performed on another widely used LM386 microcircuit that does not have an “ON/OFF” input, or simply on transistors according to any known circuit. An example of using the LM386 IC as a ULF receiver is shown in Fig. 3. In this case, transistor VT4 and resistor R20 are not installed, and points A, B and C, shown in Fig. 1 are connected to each other accordingly.

Rice. 3. An example of using the LM386 IC as a ULF receiver.

Table 1. Winding data of inductors

Printed circuit board

Printed circuit board drawings are displayed in mirror form (Fig. 4 and Fig. 5 - especially for the “printer” manufacturing method. Dimensions of printed circuit boards: transmitter and UHF receiver board 60x67.5 mm; receiver - 57.5x35 mm. Quality of printed circuit boards at using the method below turns out pretty good.

1.In graphical or text editor select the required size of the printed circuit board pattern. We print it with the maximum toner consumption per laser printer on paper from any poster. Printing must be on the reverse (white) side. The paper should have a glossy sheen. You should not print on plain paper. Do not touch the finished drawing with your hands - greasy stains will remain and the toner will not stick to the foil.

2.Cut out the printed design with a 2cm border. We place the resulting workpiece on the processed fine sandpaper foil fiberglass, cut 7...10 mm larger than necessary on all sides (do not touch it with your hands, otherwise the toner will not stick to the foil!), so that the toner is attached to the foil, and wrap the paper.

Rice. 4. Printed circuit board transmitter.

Rice. 5. Receiver circuit board.

Place it all on a hard surface and iron it for 1 minute. The time can be selected experimentally. Then let the fiberglass cool down a little and lower it into a very warm, but not hot water. After 20 minutes, carefully roll the paper into lumps until there is no paper left on the foil. If the paper remains in some places, do not worry - the acid (or other etching solution) will do its job.

3.Dip the board into the etching solution. We're poisoning. We rinse. Cut to required sizes.

If the above points are carefully followed, accuracy will depend on the preparation of the fiberglass surface. Otherwise, the paper will peel off along with the toner.

WALKIETIME SCHEMATIC

In some cases, it is not possible to use a mobile phone, but communication is needed constantly. For these purposes, it is proposed to assemble this radio circuit. The receiving part of the device is made according to classic scheme on 174ХА34. The bass amplifier can be made using transistors or the like. I used the 174XA10 microcircuit for it, or rather its part with ULF.

The transmitter can be taken from our article: or implemented on the MC2833 microcircuit, the diagram is also on the website.Let's take a look inside radio circuit diagrams:

We make the body from millimeter-thick aluminum sheets and cover it with black self-adhesive tape. A small-sized speaker with a coil resistance of 8 ohms, a microphone from a radiotelephone or tape recorder. The red LED indicates transmission, the green LED indicates power on. The 7 V source is assembled from two used cell phone batteries. The antenna is wound with PEL 0.3 wire on a TV cable without braid and central core. The receiver has frequency adjustment within the range of 105 - 110 MHz. This is done so that you can listen to FM.

This is what the finished kit looks like walkie-talkies:

It's about 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 in 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.

Winding data of coils and chokes: receiving L1 and L2, 8 turns of PEV0.6 each on a 4mm mandrel. Transmitting - 10 turns with a tap from the middle at a diameter of 4 mm. The chokes are 5-10 μH each, they are wound on 0.25-watt resistors 100-500 Ohms with a 0.2 mm wire in the amount of 50 turns. The verified version can be downloaded in the archive.

The FM band was not chosen by chance. It will be easiest for beginning radio amateurs to work with it, since the transmitter can be set up using a regular FM broadcast receiver. And after setting up the transmitter, we ensure that the receiving unit is operational. Also suitable for this is listening to FM radio broadcasting stations 88-108 MHz. Only after this you need to increase the frequency to 110-120 MHz to prevent accidental listening to your conversations on other receivers.

The operation of the units has no special features, and any “bug builder” with little experience will be able to run them without problems. The radio is powered by a 9-12V battery. Moreover, power supply from a stationary power supply is possible. This will turn it into a broadcast radio station (remember about the power limitation, according to the law). Well, the RX part works great as an FM radio receiver, which makes it possible to simply listen to music with it :)