DIY repair of VHF receivers

This experience is for a beginner who has reached the moral right to be called a "teapot" from electronics. That is, someone who already knows how to turn on a soldering iron, who understands the difference between radio components, well, at least in appearance and knows that these are electronic components. At the same time, he who has an enduring desire to bring back to life one of the electronic devices gathering dust in his closet, and with the condition of mandatory success. For starters, let it be an old “Ocean-209” radio receiver, perhaps even an old one. It is serviceable, but it is simply not possible to use it. The reason is, for example, not quite adequate sound reproduction. The first thing that needs to be learned and throughout the entire event to remember is that "in one sitting" the repair can not be overpowered, so do everything thoroughly and during the repair, do not really rely on your excellent memory, but make notes and even a photo of what you have to do in the process. He began by searching the Internet for information, and in full, about the radio receiver being restored. This is an operating manual, a diagram of the arrangement of blocks and assemblies on the chassis of a radio receiver, a schematic electrical diagram, wiring diagrams of printed circuit boards and a list of assemblies and parts used in it.

After reading the instructions and studying the circuits of the radio receiver, I unscrewed the screws and removed the back cover, side case and front panel.

He did not burden himself with super-complicated tasks, but simply, as advised by most of the luminaries of electronics, he decided to check the health of electrolytic capacitors and variable resistors, to replace the unusable ones. To do this, I removed separate units of the low-frequency amplifier and power supply from the chassis. When performing this operation, it is best to cut the connecting wires in half and put on a piece of cardboard with a written serial number at each end. There will be two cardboard boxes, but the number on them is the same. As for the wires, it is still necessary to install new ones during assembly.

I started with the power supply as the most understandable unit. It is clear from the schematic diagram that its transformer is designed to work with both 220 V and 127 V mains voltages. to get rid of 🙂

Having measured the resistance of the input windings of the transformer, I revealed the average tap for 127 V, bit off the bare end, wound it up with a ring and isolated it. The presence and location of electronic components is especially clearly visible on the wiring diagram. There is only one electrolyte of interest to me. I solder it, discharge it and measure the capacity - it is not enough to the norm of 60 μF, but the ESR probe shows the minimum allowable resistance. Therefore, I decide to put it in its place and in parallel to it solder another capacitor with a capacity of 100 μF, somewhat larger than what is lacking, but for the same voltage - 25 V. ESR acceptable value. I did it, applied the mains voltage of 220 V to the power supply unit and measured the output received - everything is normal, the power supply unit is working properly.

Now the sound amplifier. Everything is more serious here.

I find seven K50-12 electrolytic capacitors on the board, which are very ancient in appearance. I move the wiring diagram closer to me and unsolder one leg from the board from each container. Naturally where possible. Where not, the capacitor is completely evaporated.

You can completely evaporate everything, there is a mounting, but it may not be there, and then it will save a lot of time and nerves.

I checked the ESR with a probe. The one in the photo (91 millivolts) corresponds, according to the conversion table for this probe, somewhere over 30 ohms. According to the tolerance table, it can be seen that a capacitance close to 50 μF x 16 V has a limit of 1.3 ohms.

The rest, except for two, have about the same. They are not suitable for further use. For two electrolytes with a permissible ESR value, the measured capacity corresponds to the ratings - you can leave it.

I installed the necessary serviceable electrolytic capacitors on the board and removed the variable resistor - the volume control, there was too much crackling in the speaker when it was rotating. I connected an ohmmeter to it and when it rotated I saw a real "leapfrog" on the display, it was in places the current-carrying path inside its case was erased. I put a serviceable identical variable resistor and assemble the amplifier board to its original position. Now check. The output is a suitable speaker, 9 V power from a laboratory PSU, and any Chinese mini receiver-scanner can be used as a sound source. The sound is clear and there is no noise when turning the knobs.

The HF-IF unit remains. He did not take it off, and there was no need. It had poorly proven electrolytic capacitors of the K50-12 brand, so the bodies of the components were simply bitten out with side cutters and their conclusions were left on the board, to which new serviceable capacitors were soldered. The power supply and sound amplifier are back in place. Once again, having checked the correctness of the soldering of the connecting wires, I connected the radio receiver to the network. Everything worked and, most importantly, it was better than it was. And may all your work end in success, Babay.

Today we will discuss radios. A video about an old 1960 car radio from the Volga, look at YouTube, modern foreign semiconductor equivalents differ in the element base only. Lamp technology is good, giving a person an idea of ​​the principle of operation of the device. Do-it-yourself radio repair turns into a useless, hopeless task if the master is unable to figure out the actions. A person is not so surprised that dental crowns serve as a detector of a strong radio signal with an anvil-shaped speaker in the ear, if you are aware of the concept of amplitude modulation, serve as the basis for supplying information to the analogue broadcasting channel of the station. Without penetration into the circuit of a typical radio receiver, the text would turn into a read by specialists of a narrow focus, not of interest to a wide range of readers.

The receiver catches the wave, amplifies it. Extracts useful information, feeds it to the speaker. Designs are created according to the criteria:

• economic feasibility;
• quality;
• reliability.

The radio receiver begins with an input stage tuned to the desired waveform. The antenna is considered to be a relatively broadband device, picking up a large number of channels. In order to find what is needed among the mash, some kind of gate is required that allows the useful signal to pass through. The resonant circuits will serve as the portal. The theory is not important, it is useful for readers to know the following facts:

1. The resonant circuit passes a narrow section from the mass of the spectrum, the width of which is tuned to the bandwidth occupied by the channel. For example, with an amplitude modulation of 10 kHz, about that. The characteristic level at the level of 0.7 of the normalized graph demonstrates the indicated size along the horizontal axis. The shape of the frequency response is determined by the type of circuit.
2. In the simplest case, the resonant circuit is formed by inductance and capacitance connected in parallel. Not the only option. The tuning of the circuit to the frequency is carried out by varicaps (capacitor with variable capacitance). Rough channel selection is performed by a mechanical switch, transistor switches. The resonant circuits of DV, SV, VHF are different in physical terms, none of them can adapt to all ranges by changing the capacity of the varicap.
3. The resonant circuit is considered a passive element that does not carry a large electrical load, it rarely breaks. Let's trace the breakdown simply:

• only one range stopped working, it's just here, before the mixer (read below about the high-frequency amplifier);
• if, on the contrary, only one range works, the switch has broken: mechanics, transistor key.

The difficulty is the same: the high-frequency voltage of the output of the resonant circuits can hardly be measured, a typical multimeter is not designed for such an application.

RF (high frequency) amplifier wears a shield to reduce losses

The RF amplifier increases the amplitude of the incoming signal to the level of normal mixer operation. The initial frequency goes along the path, the wave differs by an order of magnitude for DV and VHF, it is impossible to execute the electronic circuit of the radio receiver on one transistor, microcircuit. It is customary to divide the input stages for FM, other frequencies. However, it concerns old models and modern ones. The high frequency amplifier is not recognized by the selective circuit - a broadband device. The explanation is simple. If the filters contained the section of the radio receiver's path, the cascades would have to be rebuilt parallel to the input resonant circuits. Complicates the design of the electrical circuit.

A fixed frequency signal is required for the detector to function properly. For FM - 10.9 MHz (frequency modulation), for LW, MW - 450 kHz (amplitude modulation). The input wave is mixed with the local oscillator frequency (high frequency reference oscillator), the output gives the difference, the values ​​are given above. The heterodyne and the mixer will essentially become amplifiers based on a transistor or microcircuit, the first one is set to the generation mode, the second works in a linear mode. The receiver is built on this type of cascade. These include the considered high-frequency amplifiers, intermediate frequency amplifiers, which we will turn to below.

Following the stabilization of the frequency, the radio receiver extracts the useful information of the broadcasting station from it. Carried out in detectors. Both stages are built on diodes, transistors, microcircuits, the difference is in the use of oscillations. With amplitude modulation, useful information is provided by the voltage swing. Consequently, the simplest diode cuts off the negative part, the envelope is obtained after filtering with an RC circuit. This is how the simplest amplitude detector works. The frequency variant is organized, for example, by a discriminator. A device in which the peak of the amplitude-frequency characteristic falls at resonance (10.9 MHz) decreases towards the edges. The result is a useful signal.

To avoid distortion, signal distortion, it must be balanced at 100% relative to the carrier. In reality, the traffic is moving, the Doppler effect, and other nuances shift the signal. Automatic frequency control comes into play. The cascade affects the resonant circuits, local oscillators, keeping the reception normal. The principle of operation is based on evaluating the symmetry of the incoming signal. The spectrum is mirrored from the carrier (in both directions). There are exceptions with one sideband, rarely used in household radios.

To save energy of the transmitter, the carrier is often cut off, leaving the pilot signal, which is usually not done for peaceful purposes, the design of the receiver becomes more complicated. The method is progressive, indicates the future. The receiver performs carrier recovery, the missing part of the spectrum according to the rule above.

The bass amplifier is a crucial part, quiet speech and music are not needed by the customers. The radio cascade is easy to find, it houses powerful microcircuits, transistors, equipped with hefty aluminum radiators. Regardless of the element base, you can achieve a screaming radio by spending power, a certain part is dissipated by heat. Overheating is blocked by radiators.

Important! Germanium is afraid of temperatures above 80 degrees Celsius. pn junctions from a semiconductor have favorable characteristics.We have to cool the power elements with radiators.

Radios have two or more channels. In case of stereo reception. The division of channels into left and right is adopted in broadcasting with frequency modulation, VHF range, including FM. The method of encrypting information is different, it does not matter when an independent repair of radio receivers is brewing. The low-frequency amplifier is a general stage, where information is fed from the amplitude detector immediately, from the frequency one - through the stereo detection circuit.

In general, it is necessary to split the radio into cascades. The purpose of the schemes was described. Forgot the power supplies for a reason, discussed the topic with reviews. In tube radios, a larger number of ratings are required. The cathodes of the lamps are heated with an alternating voltage of 6.3 V. By the way, the efficiency of the cascades can be assessed by the glow in the dark of the electrodes. Wait until the radio is warming up, then check for reddish reflections by turning off the light. You can easily understand the location of the breakdown. The burned-out lamps turn black. They can glow in a completely ordinary style. Repairing a tube radio is easier than repairing a modern one.

The device is visually divided into logical parts, you can approximately localize the malfunction. The radio receiver device often contains test contacts, another thing is where to find information. We believe that, if desired, information can be found on a specialized forum, in a technical library. Now it is not customary, remembering the good old days, to supply a radio receiver with a detailed electrical circuit, everyone who is good at it. In the case of hybrid electronics, the device can be one microcircuit, the low-frequency amplifier is separate. We'll have to find a new radio.

In other cases, you can repair transistor radios, repair tube radios. Postpone the latter to be discounted. Musicians still prefer tube amplifiers.

So, self-repair of the radio is carried out according to the indicated scheme:

1. Disassembly of the device for assessing the internal state, inspection.
2. Breaking an electrical circuit into logical parts.
3. Search for radio documentation by available channels.
4. Survey of radio amateurs on forums on topics.

We are talking about old devices - first of all we clean off the dust, watch the installation, check the tracks. If a light tapping on the device responds with the crackle of the speakers of the radio receiver, it is a broken contact. Solder cracks, peeling tracks, gaps - must be eliminated, take the trouble to re-check the functionality. In Soviet-era car radios, an inverter is used, the noise of which you will hear after switching on. Repairing old radios is useful for beginners, allowing you to learn how to use the equipment. The masters train daily. They study the types of radios, repair methods.

Many have Chinese radios in the kitchen, today we will tell you how to fix a very common breakdown with our own hands. This article will not open America to experienced radio amateurs, but it may well come in handy for novice Samodelkin. Today we will talk about how to fix the most common breakdown - crackling when working and adjusting the volume. It often happens that the receiver lives quietly and calmly, no one drops it, does not water it from the kettle, but it starts emitting a terrible rattle when trying to make it louder or quieter, and sometimes it is not possible to find the point at which the sound volume will be comfortable for you ...

The reason for this breakdown is that a low-quality variable resistor (in the form of a wheel) is installed in the receiver, on which the resistive layer quickly wears out and the contact no longer walks along the resistive layer, but along a rubbed groove in the glass-textolite base. Our experimental exhibit is a very common cheap Chinese radio receiver KIPO KB-308AC

So let's start repairing. We unscrew all the screws connecting the case, we see the board with the details.

Carefully unscrew the screws that secure the board to the case and very carefully lift the board. The fact is that from the reverse side to one of the components (variable capacitor) there is an indicator plastic plastic that runs along the display and shows the frequency to which the receiver is currently tuned.

Then we find our variable resistor and unscrew the wheel.

Having removed the wheel, you will see a plastic gasket, carefully pick it up and take it out.

And finally, before you is the hero of the occasion in all its glory.

The photo shows those trenches about which I spoke above, rubbed with a slider in the resistive layer.

Now, with the help of a match, we apply grease without skimping, here you cannot spoil the porridge with oil, you can fill the entire volume. Well, we collect in the reverse order.

We turn on, and…. it still cracks! Turn off the receiver, turn the regulator from extreme to extreme position about 30 times and ... Voila, everything works! The volume is adjusted softly and smoothly, like on his native conveyor in the Chinese village 🙂!

I hope the article will be useful to someone, during my life I have repaired many receivers in this non-tricky way.

Hello everyone, today I found a Chinese FM receiver KIPO in the attic, but what's the difference what it's called - they are almost all the same in design and scheme. I appreciated the state by eye - it seemed like everything was buzzing, the mains plug was really torn off, stripped the wires and into the outlet - silence. Yeah, we disassemble, we see everything is good, and then it dawned on me that he had been buggy for a long time, the frequency was gone, the volume disappeared, I wanted to repair it, but my hands did not reach, but no one knows how he ended up in the attic, or maybe I still remember. Let's go further - appearance.

We disassemble the receiver. To begin with, let's remove the battery compartment crimp to see if there are bolts, no - we go further and unscrew all the bolts except for the one under the antenna. You cannot touch it, it only holds a telescopic antenna. There is another hidden bolt under the handle.

So we remove the handle carefully so as not to break it, there we can see the hole on the right side, unscrew the bolt and finally remove the cover. We will unsolder all the wires, but remember where which one was.

I began to think that this was a worn out variable capacitor (with which we adjust the frequency) and of course a variable resistor (volume). Let's check. We solder the variable capacitor, since I found the same board from the receiver in the bins - here is the resistor and capacitor donor.

Below in the photo I have already soldered a variable capacitor, and clamped the contacts of a variable resistor with tweezers. Hurray, the receiver is alive!

Since the getinax is very fragile, especially the Chinese one, the tracks are very difficult to tolerate heating, they instantly peel off, broke a little but soldered the variable resistor, and to be sure, fixed it with hot glue, like this.

I forgot to say, the FM receiver is built on the popular SONY CX16918 microcircuit with very good parameters, in the future I will make another radio receiver with a sound signal amplifier on this microcircuit, and so on - winter is still ahead.

They brought me the Alpinist 320 receiver for repair with a complaint that the receiver does not catch anything but noise. But instead of simple repairs, it was necessary to expand the range of received frequencies, up to 95-108 MHz. It was decided to use a ready-made radio set.

There were a number of problems: the supply voltage of the module is limited to 7.5V, but it is better not to risk it and power the board from 5-6V, and the power supply of the receiver is 9V, a quick and hasty decision to use a roll. The internal antenna is ferrite and not suitable for FM. I removed a telescopic antenna from another radio receiver. And I bought the missing variable resistors without any problems, while the volume control left its own, although the recommended resistance is 100K according to the scheme, but the voltage between the extreme terminals is 1.25V, and I used an 8K variable resistor without any problems.
Here is the current look of the insides of the radio

But the decision to apply the roll was hasty, we have a classic power supply on one transistor, the only thing I needed to change was a zener diode, and from 9V I got 5V, there was no such zener diode, but there were two powerful ones at 2.7V, but got 5.2 - 5.3V due to a fall

Now we just take out the old insides and instead of them we attach the board of the new receiver

We solder the power wires, adjustments. ... Please note that the maximum frequency and volume are obtained by grounding the middle terminal of the variable resistors, and not by pulling it up to the power source!
To simplify the construction, I removed all unnecessary parts of the board, leaving only the resistor mountings. The antenna was soldered to a piece of PCB, which was screwed to the old PCB mount.

That's it, the new radio is in the old building, the reception is confident and clear.

JLCPCB is the largest PCB prototype factory in China. For more than 200,000 customers worldwide, we place over 8,000 online orders for prototypes and small batches of printed circuit boards every day!

Today I am starting a series of articles "Legends do not die", in which I will try to tell a little about the amazing and interesting things to which the prefix "retro" is usually added these days.

Old man ..., this magic word that caresses the ears of every connoisseur of good things, irrepressibly excites my imagination for the last couple of years. In search of interesting new products, I patrol the city markets and second-hand shops every weekend. About a month ago, a radio "Ocean - 214" got into my networks, which I mentioned in passing in my blog.

This solid apparatus of the end of the last century undoubtedly aroused the envy of ordinary mortals, since it had not only a wooden design, but also an appropriate price.

The monthly salary of an ordinary engineer is a solid jackpot for a small receiver.

And although I got this unit for a much smaller amount (in terms of today's prices), its condition left much to be desired.

Plus, after five hours, he stopped playing altogether.

Having become a little sad, I gathered my will into a fist and set to work, deciding at all costs to bring the pensioner to mind.

Restoration and repair of the radio receiver Ocean - 214

To begin with, I started disassembling.

This process is not very time consuming, but very interesting.

Good sound quality with just one paper cone speaker

While dismantling, I came across an interesting feature - the receiver either works or does not work. Most likely, bad contact has formed somewhere. The search began with the radio frequency unit,

to the extent that it was during its rotation that interruptions in work were observed.

Then he began to inspect the range shift knob.

It was then that the dog rummaged - shortened the power wire of the right backlight lamp.

After soldering, the receiver came to life and did not turn off.

Having completed a successful renovation, I decided to concentrate on the restoration. The plastic parts of the receiver have been thoroughly washed and dried. To give them a factory shine, I decided to use a colorless shoe polish.

The result was quite satisfactory for me - the details got rid of whitish stains.

The wooden body has been varnished in one layer.

Under no circumstances should the inner surface of the case be lapped, otherwise the receiver will lose all its sound properties.

The metal parts of the body have been thoroughly treated with a soapy old toothbrush.

The clear plastic windows were gently wiped with a soft monitor cloth.

On the threaded antenna tip,

clocked up a new limit switch presented to me by Mitrofanych from the radio market.

As a result of the assembly, the device acquired a solid look,

and pleased the household with such a good sound that my favorite JVC EX-A1 ​​respectfully asked permission to be photographed with the star.

Nokia 7250i also quietly crept in here.

The retired pensioner endured the move to another living space quite successfully, and even made a new friend for himself.

Solid set, for solid guys

So what do we have? Solid appearance, beautiful (albeit mono) trademark "wooden" sound, extended VHF range, and not a second of regret about the deal.

it becomes quite obvious - I invested my 422 rubles extremely well!

Until next time, friends! And as a keepsake, a modest group photo.

Thanks to my new master class, you will learn how you can repair a broken radio receiver with your own hands.

If, sorting through things in the attic or in the closet, you find an old radio, do not rush to get rid of it. With a satisfactory condition of its body, you can try to breathe life again into the device that has been lying idle for several years, or even decades, and it will still serve you in the garage, in the country or at work.

As an example, let us analyze here the situation with a radio receiver of the 2nd complexity group (which for a layman means a 2nd class receiver) Meridian-235, found by a neighbor in his bins and immediately brought in for repair.

In general, the situation is as follows:
no power cord;
when the batteries are connected, the indicators light up, but there is no sound;
the tuning knob rotates in both directions, but the tuning indicator bar does not move.

We arm ourselves with a screwdriver and open the receiver case. The naked eye can see that someone did their best: the speaker and amplifier unit LCHO-15 were removed.

The latter was used in portable radio tape recorders such as Tom, Nerl, Riga, Aelita and similar equipment, so the amplifier probably went to replace the faulty unit.

In addition, a power transformer and a power supply board were once located on the back cover - only a memory remains of them.

Despite the listed troubles, the receiver can still be restored: such speakers are still found on the radio markets; if it is not possible to find the amplifier unit LCHO-15, then the amplifier can be assembled with your own hands - on the same K174UN7 microcircuit or any other one that is suitable in terms of power and supply voltage.

The power supply board can also be made independently, and the transformer is not difficult to choose - now there are a lot of them on the market and there is plenty to choose from.

Unscrew the screws securing the board to the case and take it out. As expected, the bar of the adjustment indicator was broken: two holders are visible in the photo, and the third, located in the middle and fixing the bar on the cord of the vernier mechanism, is broken.

Repair of any radio receiver begins with checking or repairing a low-frequency amplifier. Since in our case it is completely absent, we will restore it according to the "native" scheme, except that due to the absence of a standard heatsink for cooling the microcircuit, the arrangement of parts and the layout of the tracks will change.

The new amplifier is assembled on a 42 × 60 mm board; the K174UN7 microcircuit can be found in the depths of Soviet color TVs 2USTST-3USTST and even later. We will also borrow a radiator from there.

A few words about the diagram and details.

It often happens that different manufacturers use parts with rather significantly different ratings during installation. So it is quite possible to use details of the following denominations:
C3 - 100-500 uF;
R2 - 39-68 Ohm;
C5 - 2700-4700 pF.

The parts are inserted and sealed, the ULF unit is ready for installation.

It is possible that the components listed in the previous step will have to be selected more accurately in order to set the gain to your own taste and correct the frequency response (amplitude - frequency response).

If there is a difficulty in acquiring a plastic 5-pin connector, then the same can be removed from the old SK-D-24 block, which was used in semiconductor TVs of 1980-2000.

It happens that in a hurry you sometimes forget to make a markup on the board for any part - and that's it, the board is already unusable, you need to do it again.

However, everything is not always so bad: in the red circles, you can see the soldering of the terminals of the “forgotten” capacitor - in the photo above it is red and installed across the board.

In the red rectangle you can see an SMD resistor and a capacitor under it; if necessary, the missing parts can be set in this way.

We insert the ULF into the socket and turn on the receiver. In response, we hear only noise, which increases with increasing volume, which means that our amplifier is working.

Now we are trying to tune in to some radio station of the MW or DV range. On medium waves, nothing can be found, on long waves - only one station.

Since in this receiver, instead of a KPI, an electronic tuning system is used using a resistor, we measure the voltage at its terminals - one of the extreme contacts must have a tuning voltage of 27 to 30 volts.

Checking the voltage across the variable resistor showed that the power supply was too small and was only 2 volts. If power is supplied to the PN-15 voltage converter, then its output should be 27-30V.

In the photo, the converter block is indicated by an arrow. On the reverse side of the board, on the unit contacts, we measure the voltage - and again 2V when powered by 9V.
This indicates a malfunction of the voltage converter, and in the next master class we will talk about its repair and the manufacture of a power supply for the receiver.

What is FM Receiver? A radio receiver is an electronic device that receives radio waves and converts the information carried by them into useful information for human perception. The receiver uses electronic filters to separate the desired RF signal from all other signals picked up by the antenna, an electronic amplifier to increase the signal strength for further processing, and finally recovers the desired information through demodulation.

Of the radio waves, FM is the most popular. Frequency modulation is widely used for FM broadcasting. The advantage of frequency modulation is that it has a higher signal-to-noise ratio and therefore emits RFI better than an equal power amplitude modulation (AM) signal. We hear the sound from the radio clearer and richer.

VHF (Ultra Short Wave) range with FM (Frequency Modulation) in English FM (Frequency Modulation) has a length of 10 m to 0.1 mm - this corresponds to frequencies from 30 MHz to 3000 GHz.

A relatively small area is relevant for receiving broadcast radio stations:
VHF 64 - 75 MHz. This is our Soviet range. There are many VHF stations on it, but only in our country.

Japanese range from 76 to 90 MHz. This range is broadcast in the land of the rising sun.

FM - 88 - 108MHz. Is the western option. Most of the receivers on sale nowadays necessarily work in this range. Often now, receivers accept both our Soviet range and the western one.

VHF radio transmitter has a wide channel - 200 kHz. The maximum audio frequency transmitted in FM is 15 kHz, compared to 4.5 kHz in AM. This allows a much wider range of frequencies to be transmitted. Thus, the transmission quality of FM is significantly higher than that of AM.

Now about the receiver. Below is a schematic diagram of the electronics for an FM receiver along with a description of how it works.

• Chip: LM386
• Transistors: T1 BF494, T2 BF495
• Coil L contains 4 turns, Ф = 0.7mm on a 4mm mandrel.
• Capacitors: C1 220nF
• C2 2.2 nF
• C 100 nf х 2 pcs
• C4.5 10 μF (25 V)
• C7 47 nF
• C8 220UF (25V)
• C9 100 uf (25 V) х 2 pcs
• Resistances:
• R 10 kOhm x 2 pcs
• R3 1 kΩ
• R4 10 ohm
• Variable resistance 22kOhm
• Variable capacitance 22pf
• Speaker 8 ohm
• Switch
• Antenna
• Battery 6-9V

Below is a diagram of a simple FM receiver. A minimum of components for receiving a local FM station.

Transistors (T1,2), together with a 10k resistor (R1), a coil L, a 22pF variable capacitor (VC), make up an RF generator (Colpitts oscillator).

The resonant frequency of this oscillator is set by the VC trimmer to the frequency of the transmitting station that we want to receive. That is, it must be tuned between the 88 and 108 MHz FM band.

The information signal taken from the T2 collector is fed to the LF amplifier on the LM386 through a 220nF blocking capacitor (C1) and a 22 kΩ VR volume control.

Basic electrical diagram FM receiver

Reconstruction to another station is carried out by changing the capacity of the variable capacitor 22 pF. If you use any other capacitor that has a large capacity, then try to reduce the number of turns of the L coil to tune to the FM range (88-108 MHz).

Coil L has four turns of 0.7 mm diameter enamelled copper wire. The coil is wound on a mandrel with a diameter of 4 mm. It can be wound on any cylindrical object (pencil or pen with a diameter of 4 mm).

If you want to receive a signal from VHF stations in the range (64-75 MHz), then you need to wind 6 turns of the coil or increase the capacity of the variable capacitor.

When you wind the required number of turns, the coil is removed from the cylinder and stretched a little so that the turns do not touch each other.

The LM386 is a low frequency audio power amplifier. It delivers 1 to 2 watts, which is enough for any small speaker.

An antenna is used to pick up a high frequency wave. As an antenna, you can use a telescopic antenna of any unused device. A good reception can also be obtained from a piece of insulated copper wire about 60 cm long. The optimum length of copper wire can be found experimentally.

The receiver can be powered by a 6V-9V battery.

You have to fish in different places. It also happens where heating plants or other economic services discharge water used to cool the units of thermal power plants, and a few additional degrees sometimes lead to an increased concentration of some fish species in such places.

It is well known that at temperatures above 25 ° C in sedentary and shallow waters, the degree of oxygen saturation is practically zero, and this creates conditions in which it is difficult for fish of certain species to survive.

You can, of course, buy a thermometer-hygrometer, but it is interesting and cheaper to do it yourself. In view of the excess of free temperature sensors and some other details lying around, I decided to assemble this device, which is necessary in everyday life, on the ATmega168V and SHT21. Read more ...

On the drive2 website, you can find not a single activation of various functions in MediaNav, among other things, in other blocks too.

Owners of petrol versions of Renault cars, complete with standard autostart and MediaNav, were more fortunate - from the factory they have a BIC 283468105R unit installed in their car, which switches two car buses: CAN1 and CAN2, transmitting data from the on-board computer and ambient temperature to the MediaNav screen.

On our website information will be collected on the solution of seemingly hopeless situations that arise in you, or may arise, in your everyday life at home.
All information consists of practical advice and examples on possible solutions to a particular issue at home with your own hands.
We will develop gradually, so new sections or headings will appear as materials are written.
Good luck!

Home radio - dedicated to amateur radio. The most interesting and practical circuits of devices for the home will be collected here. A series of articles on the basics of electronics for beginner radio amateurs is planned.

Electrician - given detailed installation and schematic diagrams concerning electrical engineering. You will understand that there are times when it is not necessary to call an electrician. You can solve most of the questions yourself.

Radio and Electrics for beginners - all information in the section will be completely devoted to novice electricians and radio amateurs.

Satellite - describes the principle of operation and configuration of satellite television and the Internet

Computer - You will learn that it is not such a terrible beast, and that you can always cope with it.

We repair ourselves - illustrative examples are given for the repair of household items: remote control, mouse, iron, chair, etc.

Homemade recipes - this is a "tasty" section, and it is completely devoted to culinary.

miscellanea - a large section covering a wide range of topics. These are hobbies, hobbies, useful advice, etc.

Useful little things - in this section you will find useful tips that can help you in solving everyday problems.

For home gamer - the section is entirely devoted to computer games and everything connected with them.

Works of readers - the section will publish articles, works, recipes, games, advice from readers related to the topic of home life.

Dear visitors!
My first book on electrical capacitors, dedicated to novice radio amateurs.

By purchasing this book, you will answer almost all questions related to capacitors that arise at the first stage of radio amateurism.

Dear visitors!
The site contains my second book on magnetic starters.

By purchasing this book, you no longer have to look for information about magnetic starters. Everything that is required for their maintenance and operation, you will find in this book.

Dear visitors!
The third video for the article How to solve Sudoku has been released. The video shows how to solve a difficult Sudoku.