A simple radio receiver diagram: description. old radios

With just one chip, you will need to build a simple and complete FM receiver that is capable of receiving radio stations in the 75-120 MHz band. The FM receiver contains a minimum of parts, and its setup, after assembly, is reduced to a minimum. It also has good sensitivity for receiving VHF FM radio stations.
All this thanks to the Philips TDA7000 chip, which can be bought without problems on our favorite Ali express -.

Receiver circuit

Here is the receiver schematic. Two more microcircuits are added to it, so that in the end we get a completely finished device. Let's start looking at the diagram from right to left. On the LM386 running chip, a low-frequency amplifier for a small dynamic head, which has already become a classic, is assembled. Here, I think, everything is clear. The variable resistor controls the volume of the receiver. Further, a stabilizer 7805 is added above, which converts and stabilizes the supply voltage up to 5 V. Which is necessary to power the receiver's microcircuit. And finally, the receiver itself is assembled on the TDA7000. Both coils contain 4.5 turns of wire PEV-2 0.5 with a winding diameter of 5 mm. The second coil is wound on a frame with a ferrite trimmer. The receiver is tuned to the frequency with a variable resistor. The voltage from which it goes to the varicap, which in turn changes its capacitance.
If desired, varicap and electronic control can be abandoned. And the frequency can be tuned either with a tuning core or a variable capacitor.

FM receiver board

I drew the circuit board for the receiver in such a way as not to drill holes in it, but to solder everything from the top, as with SMD components.

Placement of elements on the board

Used the classic LUT technology for the production of the board.

I printed it out, warmed it up with an iron, etched it and washed off the toner.

Soldered all the elements.

Receiver setup

After turning it on, if everything is assembled correctly, you should hear a hiss in the dynamic head. This means that everything is working fine so far. The whole setting comes down to setting the contour and selecting a range for reception. I tune by rotating the core of the coil. As the reception range is configured, the channels in it can be searched for by a variable resistor.

Conclusion

The microcircuit has good sensitivity, and a large number of radio stations are caught on a half-meter piece of wire, instead of an antenna. The sound is clear, without distortion. Such a scheme can be applied in a simple radio station, instead of a receiver on a supergenerative detector.

Once upon a time, there was a Sony radio tape recorder, during the sale they said that it was Japanese, the price made me believe, in the future he himself assured everyone that she was from there. Its objective advantage is pure sound. True, there was a small nuance - the FM range scale was 88-108 MHz, but the store had a magician who, for a "small share", created a miracle - he filled the scale with many Russian-speaking radio stations. Operated the radio full program, but remembering how much was paid for it, they did not throw it or her. So it was not badly preserved, despite the very respectable age. That's just the broadcasting stations that she caught, at first diminished, and then did not remain at all.

On the Internet, about setting up sound-reproducing equipment, there is a sea of ​​information, it is written correctly, in detail. This is happiness for students of radio engineering universities, you can easily use it instead of notes to prepare for exams, and this info will not help the owner of an ill radio, it’s not to increase his intelligence, but to fix the receiver. Or throw it away, no worries.

He opened the case, began to disassemble it into its component parts. Neither the power supply, which turned out to be super primitive, which is at the bottom left, nor the tape drive mechanism of the tape recorder, to the right of it, have no complaints. One gives out its 12 V “on the mountain”, and the second regularly pulls the magnetic tape.

But I wanted to understand the printed circuit board a little. To warm up, I checked all the electrolytic capacitors for the actual presence of capacitance and ESR. It's hard to believe, but everything turned out to be in perfect order. I soldered and disassembled the volume control - a variable resistor, for example, a revision. Once upon a time, he messed up a little and was, by means of a medical syringe with a needle, awarded a portion of engine oil. Does it need a supplement? And there was so much oil in it that even now in a frying pan - I blotted the excess, returned it to its place. I washed the circuit board from the side of the printed conductors with formic alcohol specially purchased at the pharmacy (they didn’t give anything else), and then, so that there was no white coating from it, with hot water and shampoo. It turned out not bad, although it is perceived by ear, this method is wildly.

The wire contacts suitable for the speaker were soldered. And around the circumference of the speaker, he installed a rim - a flexible tube cut along the length from a medical dropper. This is so that the metal of the speaker does not rely on the plastic of the case - it will definitely not be worse for the sound characteristics.

And then, very opportunely, I remembered that the master who was modifying the radio tape recorder spoke about some kind of wire spirals. There were several of them on the board, and everything was in the region of a variable capacitor. I partially assembled the device, turned it on and, at the desired range, began to touch the copper wires wound with rings with a screwdriver. Two did not respond, but barely touched the third, characteristic changes in sound appeared in the dynamics. Found! Pictured below. I touched it well with tweezers, and it dangles. I soldered it, straightened it and wound it on a new one, on a mandrel of a suitable diameter. Soldered into place. FM band came to life. Then he completely grew bolder and let's move the turns with a screwdriver (increase and decrease the gap between them). In response to my actions, the location and number of stations on the scale began to change. But two tweezers turned out to be the most convenient for tuning. He stretched and squeezed them like an accordion, only gently. You can clearly see this action in the video.

Video

As a result, I chose a combination of stations that was suitable for me and optimal in terms of location on the scale. The only difficulty is to do everything slowly, otherwise, you know, you want to do everything faster. Good luck! Babay iz Barnaula shared the simplest option for a possible restoration repair - settings.

Each radio has settings for a certain frequency, most of them even have fixed ones, which is very convenient. If the receiver is digital, that is, it has an electronic setting, then it will not be difficult to fix one or another radio station on a specific channel. This process will be a little more difficult on receivers with a conventional tuning scale. But, in any case, the user manual describes in detail how to tune the radio and how many stations you can store in its memory. However, all this can be done only after the purchase of this very radio. Many people are faced with the problem of choice these days, because there are a lot of all kinds of models in stores.

For those who want to listen to all radio stations, an all-wave receiver would be the best option. And if he has the opportunity to receive VHF waves, then it will be just happiness, because such receivers can also catch radio talks. Therefore, it is worth considering how to choose a radio receiver, for what purposes it will be used and what should it be? If this is a "cabinet" receiver, then standard FM and AM bands will be enough for it. For "portable" and "traveling" receivers, it is better to be able to "listen" to all frequencies, since hikes can be in unfamiliar areas where the radio can broadcast on any frequency. "Portable" you can just play around and eavesdrop on other people's conversations if they use walkie-talkies.

If you can’t buy such a receiver, then you should think about how to assemble a radio so that it can “hear” in the right range. To do this, you must be a radio amateur, or have one of them in very close friends. You can, of course, dig around the Internet and look for step by step instructions radio assembly. But there are also pitfalls there, because not all the necessary parts can be bought, some you have to do yourself. Therefore, if there is a radio amateur friend, then you can ask him how the radio works, what parts you can buy, and which ones and how to do it yourself, and most importantly from what? After the answers to the questions are received, you can start searching for the necessary parts, both for the receiver and parts for parts for your radio.

You will have to run a lot around the shops, look for old equipment in the pantry and dig into it in search of the necessary parts. After that, you will have to spend a lot of time with a soldering iron in your hands and use up a few grams of tin and wires. And now, when all the details are ready, it will be necessary to turn to a friend with the question of how to make a radio receiver so that it works reliably and for a long time. What will be the radio, it does not matter much. Both homemade and purchased receivers receive radio waves. If he brings pleasure to his master, then he will fulfill his destiny.

Dear visitors!!!

If we compare obsolete and modern models of radio receivers, they certainly have their own differences both in design and in electrical circuits. But the basic principle radio signal reception- not changeable. For modern models of radios, only the design itself changes and minor changes are made to the electrical circuits.

As for tuning the radio to a wave, then receiving transmissions in the ranges for:

• long waves \LW\;
• medium waves \SV\,

- usually carried out on a magnetic antenna. In ranges:

- reception of the sound of the radio receiver is received on a telescopic \outdoor\ antenna.

Figure 1 shows appearance and graphic designation of receiving antennas:

telescopic;

magnetic \antenna DV and SV\.

Reception-on a magnetic antenna

Figure 2 shows a visual representation of the obstruction of radio waves around obstacles \ for mountainous terrain \. The radio shadow area is represented as a zone inaccessible to radio waves by the receiver.

What is a magnetic antenna? - The magnetic antenna consists of a ferrite rod, and the coils of the magnetic antenna are wound on separate \insulated\ frames. The ferrite rod of a magnetic antenna for different radio receivers has its own diameter and length. The winding data of the coils, respectively, also have their own specific number of turns and their own inductance - for each of these circuits of the magnetic antenna.

As you understand, such concepts in radio engineering as each individual magnetic antenna circuit and magnetic antenna coil, - have the same meanings, that is, you can formulate your proposal in one way or another.

In radio receivers, in its upper part, a magnetic antenna LW and SW is mounted. In the photograph, the magnetic antenna looks like an oblong, cylindrical rod \made of ferrite\.

If each coil \ circuit \ of a magnetic antenna has its own inductance, respectively, it is designed to receive individual radio wave bands. For example, according to the electrical circuit of the radio receiver, you observe that the magnetic antenna consists of five separate circuits \L1, L2, L3, L4, L5\, two of which are necessary for the received range:

• DW \L2\;
• SW \L4\.

Other circuits L1 L3 L5 - are communication coils, one of which, let's say L5 is connected to an external antenna. This explanation is not given specifically for each diagram, because the meanings of the symbols in the diagrams may change, but is given general concept about the magnetic antenna.

Reception-on a telescopic antenna

telescopic radio antenna

Depending on the radio circuit, the telescopic \whip antenna\ can be connected both to the input circuits of the long and medium wave ranges through a resistor and a coupling coil, or to the input circuits of the short wave range - through an isolation capacitor. From the taps of the coils of the DV, SV or KV circuits - the signal voltage is applied to the input of the RF amplifier.

Winding data-antennas

The winding on the circuits is carried out with a single or double wire. Each circuit has its own inductance. The amount of inductance in a loop is measured in henries. To rewind a circuit yourself, you need to know the winding data for that circuit. That is, you need to know:

• number of turns of wire;
• wire section.

All the necessary technical data for outdated models of radio receivers could be found in reference books. At this time, there is no such literature for modern models of radio receivers.

For example, for receivers:

• Climber-405;
• Giala-404,

- the winding data of the coils coincided with each other. That is, let's say the communication coil \ and there are several of them - in the circuit \ with its designation, could be replaced from one receiver circuit to another circuit.

A circuit malfunction is more often associated with mechanical damage to the wire \ accidentally touched the wire with a screwdriver and more \. When repairing the circuit \ its rewinding \, it is usually taken into account, the number of turns of the old wire is taken into account and then the same number of turns is performed with a new wire, where its cross section is also taken into account.

In this article, we partially got an idea about the reception of sound by a radio receiver. Follow the rubric, further will be even more interesting.

Setting up a transistor receiver, in principle, differs little from setting up a tube receiver. After making sure that the bass amplifier is fixed and the tubes or transistors of the receiver are operating in normal modes, they begin to tune the circuits. The tuning starts with the detector stage, then goes to the IF amplifier, local oscillator and input circuits.

It is best to tune the circuits with a high frequency generator. If it is not there, then you can tune by ear, according to the received radio stations. In this case, only an avometer of any type (TT-1, VK7-1) and another receiver may be required, the intermediate frequency of which is equal to the intermediate frequency of the tuned receiver, but sometimes they are tuned without any instruments. The autometer during adjustment serves as an indicator of the output signal.

When setting up the IF amplifier circuits in a tube receiver, when an RF generator and a tube voltmeter are used for this purpose, the latter must not be connected to the grid of the lamp, since the input capacitance of the voltmeter is added to the capacitance of the grid circuit. When adjusting the circuits, the voltmeter should be connected to the anode of the next lamp. In this case, the circuit in the anode circuit of this lamp must be shunted with a resistor with a resistance of about 500 - 1000 Ohms.

Having finished setting up the IF gain path, they begin to set up the local oscillator and the RF amplifier. If the receiver has several bands, then the tuning starts with the KB band, and then proceed to the tuning.

Contours SV and DV ranges. Short-wave coils (and sometimes medium-wave ones), unlike long-wave ones, usually do not have cores; they are wound most often on cylindrical (and sometimes on ribbed) frames. The change in the inductance of such coils is carried out when adjusting the circuits, shifting or pushing the turns of the coils.

In order to determine whether the turns should be shifted or moved apart in a given circuit, it is necessary to bring a piece of ferrite and a brass (or copper) rod into the coil or alternately bring it closer to it. It is even more convenient to perform this operation if, instead of a separate piece of ferrite and a brass rod, a special combined indicator stick is used, at one end of which magnetite (ferrite) is fixed, and at the other - a brass rod.

The inductance of the coil of the RF amplifier circuit should be increased if, at the junction points of the circuits, the volume of the signal at the output of the receiver increases when ferrite is introduced into the coil and decreases when a brass rod is inserted, and vice versa, the inductance should be reduced if the volume increases when the brass rod is inserted and decreases with the introduction of ferrite. If the circuit is configured correctly, the weakening of the signal volume at the junction points occurs with the introduction of both ferrite and brass rods.

The contours of the MW and LW ranges are adjusted in the same order. The change in the inductance of the loop coil at the junction points is carried out on these ranges by appropriately adjusting the ferrite core.

When making homemade contour coils, it is recommended to wind a few obviously extra turns. If, when tuning the circuits, it turns out that the inductance of the circuit coil is insufficient, winding the turns on the finished coil will be much more difficult than winding the extra turns during the tuning process itself.

To facilitate the adjustment of the contours and graduation of the scale, you can use the factory receiver. Comparing the angles of rotation of the axes of the variable capacitors of the tuned receiver and the factory one (if the blocks are the same) or the position of the scale indicators, it is determined in which direction the circuit setting should be shifted. If the station on the scale of the tuned receiver is closer to the top of the scale than the factory one, then the capacitance of the tuning capacitor of the local oscillator circuit should be reduced, and vice versa, if closer to the middle of the scale, increase.

Methods for testing the local oscillator in a tube receiver. There are many ways to check if the local oscillator is working in a tube receiver: using a voltmeter, an optical tuning indicator, etc.

When using a voltmeter, it is connected in parallel with the resistor in the anode circuit of the local oscillator. If the short circuit of the capacitor plates in the local oscillator circuit causes an increase in the voltmeter readings, then the local oscillator is working. The voltmeter must have a resistance of at least 1000 ohm / V and be set to a measurement limit of 100 - 150 V.

Checking the performance of the local oscillator with an optical tuning indicator (6E5C lamp) is also simple. To do this, the control grid of the local oscillator lamp is connected with a short conductor to the grid of the 6E5C lamp through a resistor with a resistance of 0.5 - 2 MΩ. The dark sector of the tuning indicator should be completely closed during normal operation of the local oscillator. By changing the dark sector of the 6E5C lamp when turning the receiver tuning knob, one can judge the change in the amplitude of the generator voltage in different parts of the range. If the amplitude unevenness is observed within a significant range, more uniform generation over the range can be achieved by selecting the number of turns of the coupling coil.

The operation of the local oscillator of the transistor receiver is checked by measuring the voltage at the load of the local oscillator (most often at the emitter of the transistor of the frequency converter or mixer). The local oscillator voltage, at which frequency conversion is most effective, lies in the range of 80 - 150 mV in all ranges. Measurement of the voltage at the load is carried out with a lamp voltmeter (VZ-2A, VZ-3, etc.). When the local oscillator circuit is closed, its oscillations break down, which can be noted by measuring the voltage at its load.

Sometimes self-excitation can be eliminated very simple ways. So, in order to eliminate self-excitation in the IF amplification stage, a resistor with a resistance of 100 - 150 Ohms can be included in the control grid circuit of the lamp of this stage. In this case, the intermediate frequency voltage gain in the cascade will decrease slightly, since only a small part of the input signal voltage is lost on the resistance.

In transistor receivers, self-excitation can be observed if the battery of cells or batteries is discharged. In this case, the battery should be replaced and the batteries put on charge.

In a number of cases, self-excitation in the receiver and TV set can also be eliminated by such measures as transferring the grounding of individual circuit elements, altering the installation, etc. The effectiveness of the measures taken to combat self-excitation can often be assessed in the following way.

Rice. 25. To an explanation of the method for eliminating self-excitation in transistor reflex receivers

The receiver or TV is connected to an adjustable power source (that is, to a source whose voltage supplied to the anode circuits can be varied over a wide range), and a tube voltmeter or other dial indicator is turned on at the receiver output. Since at the moment of self-excitation, the voltage at the output of the receiver changes dramatically, the deviation of the indicator arrow makes it easy to note this. The voltage taken from the source is controlled by a voltmeter.

If self-excitation occurs at rated voltage, then the supply voltage is reduced to a value at which generation stops. Then they take certain measures against self-excitation and increase the voltage until generation occurs, marking it on a voltmeter. In the case of successfully taken measures, the self-excitation threshold should increase significantly.

In transistor reflex receivers, self-excitation can occur due to the poor location of the high-frequency transformer (or choke) relative to the magnetic antenna. It is possible to eliminate such self-excitation by using a short-circuited coil of copper wire with a diameter of 0.6 - 1.0 mm (Fig. 25). The U-shaped bracket of the wire is threaded through the hole in the board, bent from below, twisted and soldered to the common wire of the receiver. The bracket can serve as an element for fastening the transformer. If the transformer winding is evenly wound on a ferrite ring, then the corresponding orientation of the short-circuited turn relative to other ferrite parts is not required.

Why does the receiver "howl" on the KB band. It can often be observed that a superheterodyne receiver, when receiving a broadcasting station at short waves, begins to “howl” with a slight detuning. However, if the receiver is more accurately tuned to the received station, then reception becomes normal again.

The reason for the "howl" when operating the receiver at short wavelengths is the acoustic coupling between the receiver's loudspeaker and the tuning capacitor bank.

This generation can be eliminated by improving the depreciation of the tuning unit, as well as by reducing various accessible ways acoustic feedback - changing the way the loudspeaker is attached, etc.

Tuning the IF amplifier with another receiver. At the beginning of this section, a method for tuning a radio receiver using simple instruments was described. In the absence of such devices, the tuning of radio receivers is usually done by ear, without devices. However, it should immediately be said that this method does not provide sufficient tuning accuracy and can only be used as a last resort.

To tune the IF amplifier circuits, instead of the standard signal generator, you can use another receiver, the intermediate frequency of which is equal to the intermediate frequency of the tuned receiver. - For a tuned lamp receiver, the AGC wire from the diode to the control grids of adjustable lamps must be disconnected from the diode during tuning and connected to the chassis. If this is not done, then the AGC system will make it difficult to fine-tune the bandpass filters. In addition, when tuning the IF amplifier, it is necessary to disrupt the oscillations of the local oscillator by blocking its circuit with a capacitor with a capacity of 0.25 - 0.5 microfarads.

The auxiliary receiver used in this case does not need to be subjected to any significant alterations. To set up, you need only a few additional parts: a variable resistor (0.5 - 1 MΩ), two fixed capacitors and two or three fixed resistance resistors.

Setting up the amplifier circuits. IF receiver produced as follows. The auxiliary receiver is pre-tuned to one of the local stations operating in the long or medium wave band. Next, the common wires or chassis of both receivers are connected to each other, and the wire going in the tube receiver to the control grid of the lamp of the first IF amplification stage of the auxiliary receiver is disconnected and connected to the control grid of the lamp of the corresponding IF amplifier stage of the tuned receiver. In the case of tuning a transistor receiver, the IF signal through capacitors with a capacity of 500 - 1000 pF is fed in turn to the bases of the transistors of the corresponding stages of the IF amplifier.

Then both receivers are turned on again, however, in order to avoid interference during tuning, the low-frequency part of the auxiliary, as well as the local oscillator of the tuned receiver, should be turned off (in tube receivers, by removing the lamps, respectively, of the bass amplifier and local oscillator).

When setting up the IF amplifier stages of a transistor receiver, its local oscillator should be turned off by installing a jumper in the local oscillator circuit.

After that, by applying an intermediate frequency signal from the auxiliary receiver to the input of the tunable IF amplifier and smoothly adjusting the setting of the IF circuits of the latter, one achieves the audibility of the station to which the auxiliary receiver is tuned. Further, the tuning is continued - separately for each circuit (to the maximum signal level), and the tuning is best done using a pointer device connected to the output of the bass amplifier, or by an optical indicator (6E5C lamp or the like).

Start tuning from the last IF circuit; the signal is fed to the base of the corresponding transistor or directly to the grid of the lamp, in the anode circuit of which the tuned circuit is included.

If the adjustment is carried out not by an optical indicator, but by the sound volume, then it is recommended to set the volume level to the minimum, since the human ear is more sensitive to changes in the volume level with weak sounds.

About tuning the receiver for radio stations. The tuning of a superheterodyne receiver - tube or transistor - for received stations without the use of an auxiliary receiver usually starts on the KB band. By adjusting the IF circuits for maximum noise and rotating the tuning knob, the receiver is set to any of the audible stations. If it is possible to receive such a station, then they immediately begin to adjust the IF circuits, achieving maximum audibility (the tuning starts from the last IF circuit). Then the heterodyne and input circuits are tuned, first on short, then on medium and long waves. It should be noted that tuning receivers using this method is complex, time-consuming and requires experience and skills.

Lamp 6E5C - indicator when setting up. According to the sound volume, it is not recommended to adjust the receiver circuits, as already mentioned, especially if a high output volume level is set. The sensitivity of the human ear to changes in signal level at loud sounds is very low. Therefore, if you still have to tune the receiver by sound, then the volume control should be set to a low level, or, better, use an optical tuning indicator - a 6E5C lamp or another similar one.

Tuning superheterodyne receivers according to received stations and using a 6E5C lamp as an indicator of tuning accuracy, it is more convenient to adjust the circuits at an input signal level at which the dark sector of this lamp narrows to 1 - 2 mm.

To regulate the signal voltage at the receiver input, in parallel with the antenna coil, for example, a variable resistance resistor can be connected, the value of which, depending on the sensitivity of the receiver, can be selected in the range from 2 to 10 kOhm.

How to detect a faulty stage in an RF amplifier. When adjusting or repairing a receiver, a cascade in which there is a malfunction can be detected using an antenna, connecting it in turn to the bases of transistors or to the grids of amplifier lamps and determining by ear by noise whether there are malfunctions in these cascades.

This method is convenient to use in cases where there are several stages of RF amplification.

An antenna in the form of a piece of wire can also be used when checking the IF and RF amplification stages in TVs. Since shortwave stations often operate at frequencies close to the intermediate frequency of TVs, listening to these stations will indicate that the sound channel is working,