Are you tired of paying for mobile communications all the time? Do you want to upgrade to a free plan? Or do you want to have constant, free communication with your boys in the area? Then this walkie-talkie circuit, which you can assemble with your own hands, is for you.
To make one radio you need:
- Transistors: P416B (3 pcs) and MP42 (4 pcs);
- Resistors: 3K (2 pieces), 160K (2 pieces), 4.7K (2 pieces), 22K, 36K, 100K, 120K, 270K, 6.8K (6 pieces);
- Capacitors: 10MK*10V (2pcs), 3300MK (2pcs), 1000MK (2pcs), 100MK (2pcs), 6MK (2pcs), 5-20MK (2pcs), 22MK, 10MK, 0.047MK, 5MK*10V (4pcs);
- Antenna;
- Microphone, speaker;
- Switch, switch;
- DC source;
- Textolite boards (2 pcs);
- Wires;
- Wire with a diameter of 0.1 mm. and 0.5 mm.
Diagram of a simple homemade walkie-talkie:
How to make a walkie-talkie with your own hands
The common antenna for receiving and sending the signal is A1.
Power switch – SA1.
The switch connecting the homemade radio station with the current source, while sending the signal to the transmitter and receiver upon receipt - SA2.
Number of turns:
Coils L1 and L5 – 10 turns.
Coil L2 has 4 turns and is located between the halves of the winding of coil L3 containing 8 turns and having a wire tap in the middle.
Coils L4 and L6 – 200 turns, 0.1 mm wire around the MLE-0.5 resistor with min. resistance 1Mohm.
Well, the coils for the radio are ready.
If you still have the desire to make DIY walkie-talkies, then you probably understand at least something in electronics, and that means it won’t be difficult for you to place the parts on two boards (one of which has a master oscillator, and the other with a receiver and a low-frequency amplifier) on one side and connect them with an insulated wire ( diameter 0.2-0.3mm) on the other. Then connect using a stranded wire insulated with vinyl chloride to the battery.
Printed wiring can be done if you have foil getinaks, and for the frame of a homemade walkie-talkie, centimeter-sized pieces of wire driven into holes with a diameter of 1 mm are suitable.
The windings of the coils and chokes should be mutually perpendicular, and the C15 handle should be on the front panel of the radio. The generator must be separated from other parts by a tin screen.
Configuring and debugging the radio
Debugging begins with improving the reception quality; to do this, you need to replace R10 with a variable one with a resistance of 33-47 kOhm and wait for the maximum noise volume. Next, using a tuning core, we change the inductance L5, achieving the highest quality signal. After this, we return the previous resistor.
(the simplest walkie-talkie) is shown in Figure 1.
The radio intercom contains only three transistors. In the receiving mode, a supergenerative detector is implemented on VT1, and in the transmitting mode, the cascade on this serves as a master oscillator, emitting a carrier frequency into the antenna.
On transistors VT2, VT3 in the receiving mode serves as an amplifier of the low-frequency received signal, and in the transmitting mode it switches as an amplifier. DEM capsule, used as a microphone during transmission.
Details
Coil L1 is wound turn to turn on a frame with a diameter of 8 mm with an SCR core and has 9 turns of PEL wire with a diameter of 0.5 mm. Coil L2 is wound on top of it and has 3 turns of the same wire. Its diameter is 5 mm, it contains 60 turns of PEL wire with a diameter of 0.5 mm. The primary winding of the output transformer of a pocket transistor receiver can be used as inductor L4.
The radio station is designed for operation in a car, boat or stationary environment. It requires a constant voltage source of 12 - 15 V with at least 1 A. The communication range with a similar radio station is about 2 - 5 km in the city, up to 15 km on the highway and up to 30 km when operating in a stationary mode on a full-size antenna located on mast. The radio station operates with an antenna having a characteristic impedance of 75 ohms.
TECHNICAL CHARACTERISTICS OF CAR SV RADIO STATION
- Operating range................................................... ........................... 27 MHz.
- Transmitter output power at voltage
- Frequency modulation with deviation.................................................... .......2.5 kHz.
- Transmission current consumption, no more................................................... ......0.6 A.
- Receive current consumption, no more................................................... ......0.015 A.
- The sensitivity of the receiver with a signal-to-noise ratio is no worse than................1 µV.
- Selectivity in the adjacent channel at a detuning of ±10 kHz is no worse....... 36 dB.
12V power supply at 75 Ohm load............................................... ....................3 W.
The circuit of a pocket radio station (see Fig. 1) does not contain scarce elements, is easy to configure and simple to build. However, despite its simplicity, it has good characteristics. Receiver sensitivity is no worse than 10 μV, transmitter power is 250 mW, operating frequency is 27.14 MHz, communication radius in open areas is up to 1 km.
The transistorized pocket radio receiver is super-regenerative (VT2) and aperiodic (VT1). A useful signal is released at resistor R5, but it is much smaller with the suppression frequency of the super-regenerator. To suppress unnecessary noise and highlight the useful signal, the C12R7C13L7C14 filter is installed in the receiver. From it, the signal is supplied to resistor R13, which is a volume control, and then to audio frequency, made on transistors VT8, VT10, VT11.]
The transmitter of the pocket radio station is assembled on five transistors VT3-VT7 and is a push-pull self-oscillator, the signal of which is fed to the antenna through the coupling coil L2 and the matching circuit L1C3. Parallel connection of VT3, VT6 and VT4, VT7 allows you to increase the power transmitted to the transmitter antenna.
The use of portable radio microphones is usually associated with power supply problems, due to the need to regularly recharge batteries or change batteries. At the same time, autonomous power supply is not always necessary. The proposed radio microphone is designed to be powered by a voltage of 220 V, but differs from conventional circuits containing a network transformer or a quenching capacitor. Due to the low current consumption, it was possible to use quenching resistors, which have significantly smaller dimensions. The principle of a “network” radio microphone is shown in the figure below:
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The full-wave rectifier is assembled using diodes VD2 and VD3, voltage is supplied to it through quenching resistors R4, R5, and VD1 (about 8 V) is stabilized from the output of the rectifier.
Thanks to cascode connection
Modern element base makes it possible to create radio-electronic devices with excellent technical characteristics, minimal dimensions 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 a higher output power, better sensitivity of the noise suppression system (NSS), 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. Figure 1 shows a schematic electrical diagram of the radio station. 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 of a 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 receive mode, you should adjust the IF circuit according to the received signal (or pre-adjust it to the maximum noise level with the PN system turned off; and finally, according to the received signal). The UHF input circuits are then 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
| Coil | Frame diameter, mm | Core | Number of turns | Wire diameter, mm |
| L1 | 5 | from SB-12 (trimmer) | 15 | 0,3 |
| L2, L3, L5, L11, L14 | 5 | from SB-12 (trimmer) | 7 | 0,5 |
| L4 | over L3 | - | 3,75 | 0,5 |
| L12 | over L11 | - | 3,75 | 0,5 |
| L13 | over L14 | - | 3,75 | 0,5 |
| L7, L8 | 5,5 | - | 8 | 0,8 |
| L6, L9, L10 | - | standard throttle D-0.1 | - | - |
| L15 | 4 | SB-12 (assembled) | 80 | 0,1 |
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 a graphic or text editor, select the required size of the printed circuit board design. We print it with maximum toner consumption on a 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 foil fiberglass treated with fine sandpaper, 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. Transmitter circuit board.
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 laminate cool a little and lower it into 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.
For a long time, radios topped the list of the most significant inventions of mankind. The first such devices have now been reconstructed and changed in a modern way, but little has changed in their assembly circuit - the same antenna, the same grounding and an oscillating circuit for filtering out unnecessary signals. Undoubtedly, circuits have become much more complicated since the time of the creator of radio, Popov. His followers developed transistors and microcircuits to reproduce a higher quality and energy-consuming signal.
Why is it better to start with simple circuits?
If you understand the simple one, you can be sure that most of the path to success in the field of assembly and operation has already been mastered. In this article we will analyze several circuits of such devices, the history of their origin and the main characteristics: frequency, range, etc.
Historical reference
May 7, 1895 is considered the birthday of the radio receiver. On this day, the Russian scientist A.S. Popov demonstrated his apparatus at a meeting of the Russian Physicochemical Society.
In 1899, the first radio communication line, 45 km long, was built between and the city of Kotka. During World War I, direct amplification receivers and vacuum tubes became widespread. During hostilities, the presence of a radio turned out to be strategically necessary.
In 1918, simultaneously in France, Germany and the USA, scientists L. Levvy, L. Schottky and E. Armstrong developed the superheterodyne reception method, but due to weak electron tubes, this principle became widespread only in the 1930s.
Transistor devices emerged and developed in the 50s and 60s. The first widely used four-transistor radio, the Regency TR-1, was created by German physicist Herbert Mathare with the support of industrialist Jakob Michael. It went on sale in the US in 1954. All old radios used transistors.
In the 70s, the study and implementation of integrated circuits began. Receivers are now being developed through greater integration of nodes and digital signal processing.
Device characteristics
Both old and modern radios have certain characteristics:
- Sensitivity is the ability to receive weak signals.
- Dynamic range - measured in Hertz.
- Noise immunity.
- Selectivity (selectivity) - the ability to suppress extraneous signals.
- Self-noise level.
- Stability.
These characteristics do not change in new generations of receivers and determine their performance and ease of use.
The principle of operation of radio receivers
In the most general form, USSR radio receivers worked according to the following scheme:
- Due to fluctuations in the electromagnetic field, alternating current appears in the antenna.
- The oscillations are filtered (selectivity) to separate information from noise, i.e., the important component of the signal is isolated.
- The received signal is converted into sound (in the case of radio receivers).
Using a similar principle, an image appears on a TV, digital data is transmitted, and radio-controlled equipment (children’s helicopters, cars) operates.
The first receiver was more like a glass tube with two electrodes and sawdust inside. The work was carried out according to the principle of the action of charges on metal powder. The receiver had a huge resistance by modern standards (up to 1000 Ohms) due to the fact that the sawdust had poor contact with each other, and part of the charge slipped into the air space, where it was dissipated. Over time, these filings were replaced by an oscillating circuit and transistors to store and transmit energy.
Depending on the individual receiver circuit, the signal in it may undergo additional amplitude and frequency filtering, amplification, digitization for further software processing, etc. A simple radio receiver circuit provides for single signal processing.
Terminology
An oscillating circuit in its simplest form is a coil and a capacitor closed in a circuit. With their help, you can select the one you need from all the incoming signals due to the circuit’s own frequency of oscillation. USSR radios, as well as modern devices, are based on this segment. How does it all work?
As a rule, radio receivers are powered by batteries, the number of which varies from 1 to 9. For transistor devices, 7D-0.1 and Krona type batteries with a voltage of up to 9 V are widely used. The more batteries a simple radio receiver circuit requires, the longer it will work .
Based on the frequency of received signals, devices are divided into the following types:
- Long-wave (LW) - from 150 to 450 kHz (easily scattered in the ionosphere). What matters are ground waves, the intensity of which decreases with distance.
- Medium wave (MV) - from 500 to 1500 kHz (easily scattered in the ionosphere during the day, but reflected at night). During daylight hours, the radius of action is determined by grounded waves, at night - by reflected ones.
- Shortwave (HF) - from 3 to 30 MHz (do not land, are exclusively reflected by the ionosphere, so there is a radio silence zone around the receiver). With low transmitter power, short waves can travel long distances.
- Ultrashortwave (UHF) - from 30 to 300 MHz (have a high penetrating ability, are usually reflected by the ionosphere and easily bend around obstacles).
- - from 300 MHz to 3 GHz (used in cellular communications and Wi-Fi, operate within visual range, do not bend around obstacles and propagate in a straight line).
- Extremely high frequency (EHF) - from 3 to 30 GHz (used for satellite communications, reflected from obstacles and operating within line of sight).
- Hyper-high frequency (HHF) - from 30 GHz to 300 GHz (they do not bend around obstacles and are reflected like light, they are used extremely limited).
When using HF, MF and DV radio broadcasting can be carried out while being far from the station. The VHF band receives signals more specifically, but if a station only supports it, then you won’t be able to listen on other frequencies. The receiver can be equipped with a player for listening to music, a projector for displaying on remote surfaces, a clock and an alarm clock. The description of the radio receiver circuit with such additions will become more complicated.
The introduction of microcircuits into radio receivers made it possible to significantly increase the reception radius and frequency of signals. Their main advantage is their relatively low energy consumption and small size, which is convenient for portability. The microcircuit contains all the necessary parameters for downsampling the signal and making the output data easier to read. Digital signal processing dominates modern devices. were intended only for transmitting an audio signal, only in recent decades the design of receivers has developed and become more complex.
Circuits of the simplest receivers
The circuit of the simplest radio receiver for assembling a house was developed back in Soviet times. Then, as now, devices were divided into detector, direct amplification, direct conversion, superheterodyne, reflex, regenerative and super-regenerative. Detector receivers are considered the simplest to understand and assemble, from which the development of radio can be considered to have begun at the beginning of the 20th century. The most difficult devices to build were those based on microcircuits and several transistors. However, once you understand one pattern, others will no longer pose a problem.
Simple detector receiver
The circuit of the simplest radio receiver contains two parts: a germanium diode (D8 and D9 are suitable) and a main telephone with high resistance (TON1 or TON2). Since there is no oscillatory circuit in the circuit, it will not be able to catch signals from a specific radio station broadcast in a given area, but it will cope with its main task.
To work, you will need a good antenna that can be thrown onto a tree, and a ground wire. To be sure, it is enough to attach it to a massive piece of metal (for example, to a bucket) and bury it a few centimeters into the ground.
Option with oscillating circuit
To introduce selectivity, you can add an inductor and a capacitor to the previous circuit, creating an oscillating circuit. Now, if you wish, you can catch the signal of a specific radio station and even amplify it.
Tube regenerative shortwave receiver
Tube radio receivers, the circuit of which is quite simple, are made to receive signals from amateur stations at short distances - in the ranges from VHF (ultra-short wave) to LW (long wave). Finger battery lamps work on this circuit. They generate best on VHF. And the resistance of the anode load is removed by low frequency. All details are shown in the diagram; only the coils and inductor can be considered homemade. If you want to receive television signals, then the L2 coil (EBF11) is made up of 7 turns with a diameter of 15 mm and a 1.5 mm wire. 5 turns are suitable.
Direct amplification radio receiver with two transistors
The circuit also contains a two-stage low-frequency amplifier - this is a tunable input oscillatory circuit of the radio receiver. The first stage is an RF modulated signal detector. The inductor coil is wound in 80 turns with PEV-0.25 wire (from the sixth turn there is a tap from below according to the diagram) on a ferrite rod with a diameter of 10 mm and a length of 40.
This simple radio receiver circuit is designed to recognize powerful signals from nearby stations.
Supergenerative device for FM bands
The FM receiver, assembled according to E. Solodovnikov’s model, is easy to assemble, but has high sensitivity (up to 1 µV). Such devices are used for high-frequency signals (more than 1 MHz) with amplitude modulation. Thanks to strong positive feedback, the coefficient increases to infinity, and the circuit goes into generation mode. For this reason, self-excitation occurs. To avoid it and use the receiver as a high-frequency amplifier, set the coefficient level and, when it reaches this value, sharply reduce it to a minimum. For continuous gain monitoring, you can use a sawtooth pulse generator, or you can do it simpler.
In practice, the amplifier itself often acts as a generator. Using filters (R6C7) that highlight low-frequency signals, the passage of ultrasonic vibrations to the input of the subsequent ULF cascade is limited. For FM signals 100-108 MHz, coil L1 is converted into a half-turn with a cross-section of 30 mm and a linear part of 20 mm with a wire diameter of 1 mm. And coil L2 contains 2-3 turns with a diameter of 15 mm and a wire with a cross-section of 0.7 mm inside a half-turn. Receiver amplification is possible for signals from 87.5 MHz.
Device on a chip
The HF radio receiver, whose circuit was developed in the 70s, is now considered the prototype of the Internet. Shortwave signals (3-30 MHz) travel great distances. It is not difficult to set up a receiver to listen to broadcasts in another country. For this, the prototype received the name world radio.
Simple HF receiver
A simpler radio receiver circuit lacks a microcircuit. Covers the range from 4 to 13 MHz in frequency and up to 75 meters in length. Power supply - 9 V from the Krona battery. The installation wire can serve as an antenna. The receiver works with headphones from the player. The high-frequency treatise is built on transistors VT1 and VT2. Due to capacitor C3, a positive reverse charge arises, regulated by resistor R5.
Modern radios
Modern devices are very similar to radio receivers in the USSR: they use the same antenna, which produces weak electromagnetic oscillations. High-frequency vibrations from different radio stations appear in the antenna. They are not used directly to transmit a signal, but carry out the operation of the subsequent circuit. Now this effect is achieved using semiconductor devices.
Receivers were widely developed in the mid-20th century and have been continuously improving since then, despite their replacement by mobile phones, tablets and televisions.
The general design of radio receivers has changed slightly since Popov's time. We can say that the circuits have become much more complicated, microcircuits and transistors have been added, and it has become possible to receive not only an audio signal, but also to build in a projector. This is how receivers evolved into televisions. Now, if you wish, you can build whatever your heart desires into the device.
However, the forum received fair comments and requests for a more detailed explanation of the operation and drawings of the circuit. Therefore, after delving into the archives, I present additional materials. In those distant 90s, one could only dream of the sPlan program, and indeed of a personal computer in general - on a PC costing 500 bucks you couldn’t really do much with a $5 stipend. So below are pictures of pages from the notebook (those who wish can convert them into a more readable form).
Here the walkie-talkie is divided into two completely independent units - a receiver and a transmitter, both broadcasting in the FM range of 88-108 megahertz. This frequency was not chosen by chance - many have a ready-made FM radio receiver, which makes it possible to simplify the manufacture of a walkie-talkie, making only the transmitting part. In addition, you can listen and speak at once if you separate the frequencies of the receiver and transmitter by 10-20 megahertz.
Naturally, you can and even need to assemble the receiver yourself, using the most common K174XA34 microcircuit or its foreign analogue. The microcircuit is very unpretentious in setting up and starts up almost immediately. See the drawing of the printed circuit board for the receiving part of the radio below.
The transmitter can be made using various schemes: with 3 transistors without frequency stabilization (like a simple FM bug) or with a quartz resonator. The second option is more difficult to set up, but also better.
The figure shows that the microphone amplifier is a UD1208 op-amp. Next, the signal goes to the modulator (varicap and quartz), the quartz frequency is several times lower than the FM and the output transistor selects the desired harmonic.
Initially, the output stage circuit included a KT610 transistor, but after it burned out and there was no similar one, I installed a microwave transistor from a television to replace it - it worked even better (only the hole remained). Photos of circuits and boards are not of high quality. For a more detailed study, download the archive.
Installation of the entire transceiver unit on a fiberglass board. The receiver and the radio transmitter are assembled as a separate unit.
By the way, you may ask: Why not use a regular mobile phone as a walkie-talkie? Firstly, harmful radiation (2 GHz half a watt, versus 0.1 GHz 0.05 watts). Secondly, the power supply - a mobile battery will not last long, but here, using good banks, you can talk continuously for at least a day. And finally, mobile cellular stations are not available everywhere.
How to make a radio body. There are a lot of options, but it is best to bend it from sheet aluminum or use a ready-made shielded box. Especially if you do not have a quartz transmitter. Paint the outside of the body or cover it with self-adhesive tape.
The photo shows an option with two regulators - one is responsible for the volume, and the other is for setting the receiver frequency. After all, ours is not quartz-coated, so a little maintenance is possible in case of shocks or vibrations. On the other hand, it’s even better - you’ll listen to music on it :)
You can power your homemade walkie-talkie from anything. Voltage is 5-12 V. Naturally, with less power, the range will be shorter, although performance remains the same at 5 V.
In order to save space and current consumption, the speaker can be replaced with security-type headphones. Or provide a socket for connecting them, with automatic switching off of the loudspeaker. In general, the result is a good, personally tested design of an FM radio, which can be repeated even by not very experienced radio amateurs.
