Schemes of detector receivers. Homemade radio receiver for young radio amateurs. Device and assembly

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 background

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:

1. Sensitivity is the ability to receive weak signals.
2. Dynamic range - measured in Hertz.
3. Noise immunity.
4. Selectivity (selectivity) - the ability to suppress extraneous signals.
5. Self-noise level.
6. 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:

1. Due to fluctuations in the electromagnetic field, alternating current appears in the antenna.
2. The oscillations are filtered (selectivity) to separate information from noise, i.e., its important component is isolated from the signal.
3. 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:

1. 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.
2. 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.
3. 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.
4. Ultrashortwave (UHF) - from 30 to 300 MHz (have a high penetrating ability, are usually reflected by the ionosphere and easily bend around obstacles).
5. - 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).
6. Extremely high frequency (EHF) - from 3 to 30 GHz (used for satellite communications, reflected from obstacles and operating within line of sight).
7. 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 oscillatory 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 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 the model of E. Solodovnikov, 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.

The detector radio receiver is not afraid of short circuits between parts or their incorrect connections, so it is convenient to carry out a wide variety of experiments with it, allowing you to better understand the principle of operation of the radio receiver and learn how to independently tune it to the desired radio stations.

The diagram of the simplest detector radio receiver is shown in Fig. R-1. Inductor L1 is one of the main elements of the radio receiver. Another such element is the tuning capacitor C1. Together with the inductor, it forms a so-called oscillatory circuit, which allows you to tune the receiver to the selected radio station. The trimmer capacitor consists of two parts: a fixed one, called the stator, and a movable one, called the rotor. By turning the rotor, the capacitance of the capacitor is changed and the circuit is tuned to the wavelength of a particular radio station. In this case, the signal magnitude on the circuit, that is, at the coil terminals, increases.

This signal is further fed to a device called a detector and consisting of a semiconductor diode VD1, a permanent capacitor C2 and headphones BF1. The detector converts the radio station signal so that an alternating audio frequency current begins to flow through the headphones. And it, in turn, is converted by phones into sound. Telephones allow you to hear radio broadcasts. In order for the transmission to be heard as loudly as possible, you need to connect a good outdoor antenna to the receiver (to socket XS1) and grounding (to socket XS2).

To build a receiver, you first need to purchase a tuning capacitor C1 type KPK-3 with tabs for mounting. As a last resort, a KPK-2 capacitor without legs will do, then it will have to be attached to the receiver board through the central hole with a screw and nut.

In any case, when the capacitor rotor rotates, its capacitance should change from 25 to 150 pF. These limits of change on the capacitor body are indicated as follows: 25/150. Capacitor C2 - KSO-2 or another, with a capacity of 2000 to 4700 pF. The diode can be taken from any of the D2 or D9 series (for example, D2A, D2B, D9A, D9B, D9V, etc.). Headphones must be high-impedance, for example TON-1, TON-2. If you have other types of phones, measure their resistance by connecting an ohmmeter to the pins of the plug - it should be at least 3000 Ohms. Otherwise, you will not be able to obtain sufficient sound volume. Perhaps the capsules will be high-resistance, but connected in parallel. Then connect the capsules in series to get the desired results.

Sockets XS1 and XS2 can be either ready-made (for example, terminals, clamps) or home-made. In the latter case, it is convenient to use the sockets of a regular power outlet. To do this, the socket is disassembled, the sockets are unscrewed, their shanks are bent and the sockets are attached to the receiver panel.

Connector XI can be easily made from tin from a tin can (Fig. P-2) and thick plywood or other insulating material. A plank is cut out of plywood and two holes with a diameter of 4.5 mm are drilled in it, the distance between their centers should be 19 mm (for a standard headphone plug). For nests, a blank is cut out of tin, cuts are made on it with scissors and the blank is pressed around a fork. The resulting cylinder is inserted into the hole of the plank, the edges of the cylinder are bent using cores (or thick nails) and the bends are straightened with a hammer. The strip with sockets is attached to the mounting panel of the receiver with an M3 screw, but pre-drill holes with a diameter of 7...8 mm in the panel opposite the sockets and pass conductors through them, pre-soldered to the bends of the sockets.

It is most convenient to wind the inductor coil (Fig. P-3) on a cardboard frame with the following parameters: outer diameter 20 mm, length 58... ...60 mm, wall thickness 1...2 mm. If you don’t have a ready-made frame, you can glue it together from thick paper. At the top and bottom of the frame, contacts are installed for the coil terminals. To do this, two holes are pierced in the frame with an awl and pieces of tinned copper wire are passed through them. In addition, if the frame is homemade, you need to attach two tin tabs to it at the bottom, with which the frame will be attached to the receiver panel. The coil is wound with copper wire in enamel insulation (wire grade PE, PEL and PEV) with a diameter of 0.15...0.25 mm. The beginning of the wire is soldered to the upper contact of the frame. To do this, remove the insulation from the end of the wire at a length of approximately 10... ...15 mm. This can be done using a razor blade or fine-grained sandpaper. Then the wire is tinned and only then soldered to the contact. The wires are wound turn to turn to form a continuous winding. A total of 135 turns need to be laid. The end of the wire is soldered to the bottom contact of the frame.

So, all the parts are prepared, you can place them on the receiver board (Fig. P-4). Cut the board itself from any insulating material (getinaks, textolite, plywood) with a thickness of at least 1.5 mm. Board dimensions 70X125 mm. On the board, pre-arrange the coil, trimmer capacitor, sockets, connector, mark their attachment points and drill holes of the required diameter. In the corners of the board, make holes with a diameter of 3 mm for stands - plastic caps from tubes of toothpaste.

In the places shown as dots in the drawing, install wire stud posts made of tinned copper wire with a thickness of at least 1 mm. If you do not have such wire among your supplies, take copper wire in enamel insulation, remove the insulation with a razor blade or sandpaper and tin the wire with a powerful ohm. Cut pins 8...10 mm long from this wire. Then drill holes in the board with a diameter slightly smaller than the thickness of the studs, and insert the studs into them so that they protrude approximately the same length from the bottom and top of the board. The pins, of course, must sit tightly in the board without popping out. As a last resort, they can be slightly flattened on both sides of the board with pliers. In the future, using this method, you will make circuit boards for all assembled structures.

It's time to fix the parts on the board and connect them together in accordance with the diagram. Fig. will help you with this. R-5. It shows a drawing of the circuit board and a diagram of the connections of the parts. They show the relative position of parts on the board and the connection of their pins. The leads of the diode and permanent capacitor are pre-bent, the ends are twisted into a ring and soldered to the studs. The coil contacts are connected to the studs with pieces of mounting wire (single-core copper wire can also be used). The input sockets are connected to the studs with copper wire. The sockets of connector X1 are connected to the pins, to which capacitor C2 is soldered, at the bottom of the board.

It's time to set up the receiver. Having connected the antenna to socket XS1, grounding to socket XS2, and headphones to socket X1, slowly rotate the rotor of the trimming capacitor. Its capacitance changes from minimum (25 pF) to maximum (150 pF) when the rotor is rotated half a turn, that is, 180°. But, unfortunately, there are no marks on the capacitor body for the initial and final capacitances. Therefore, you will have to turn the rotor a full turn and try to catch at least one radio station. Since the receiver is designed to operate in the medium wave range from approximately 600 to 400 m, the most likely station that can be heard over most of our country is “Mayak” (547 m).

If you are unable to receive any radio stations, try changing the receiver's tuning range. The easiest way to do this is to use a ferrite rod with a diameter of 8 mm and a length of at least 100 mm from the magnetic antenna of transistor radios. Slowly insert it into the coil frame (Fig. P-6). The receiver will tune to longer waves, and you will probably hear the local radio station. Having lowered the rod inside the frame to the possible length, smoothly tune the receiver with the adjusted capacitor in the new range.

It is possible that the station will be clearly audible if the rod is not fully inserted. Then make a simple clamp for the rod. Cut a strip of thick cardboard a little longer than the diameter of the frame and cut a hole in its center into which the rod should fit with friction. Place the strip on the coil frame and, holding it with your hand, move the rod to tune in to the radio station. Now the rod will be held in the desired position by the locking strip.

The insertion of the rod into the frame indicates that in order to receive a radio station that is clearly audible in your area, the inductor must have a larger number of turns. The task is, of course, simple, and you can easily cope with it. Unsolder the lower terminal of the coil from the contact, connect the end of the same wire to the terminal and wind up 165 turns (now the total number of turns of the coil will be 300). Winding must be done turn to turn. When you reach the end of the frame, wind the wire over the existing winding, but in the opposite direction - to the top contact. Connect the end of the winding to the bottom contact.

Tune the receiver to a radio station using the capacitor. By rotating the rotor in a circle, you will notice that the station is audible in two positions, since the capacitance of the capacitor will change its value twice from maximum to minimum. This feature of the capacitor design can be used to assess the correct selection of the number of turns of the coil. If both settings are a fair distance apart, everything is fine. When you notice that both settings are located next to each other or almost merge into one, it means that the number of turns of the coil is not selected accurately.

It remains to determine in which direction to change the number of turns of the coil. A ferrite rod will help answer this question. Insert it inside the coil frame so that the sound volume decreases, and then try to achieve the previous volume by rotating the capacitor rotor. If you managed to do this, then you need to increase the number of turns of the coil by several tens and check the tuning to the radio station again. If, when the rotor rotates, the volume drops even more, you will have to rewind several dozen turns. So, by unwinding or adding turns of the coil, you can tune the receiver to any long or medium wave radio station that is clearly audible in a given area.

You can do interesting experiments with the assembled detector receiver. After tuning into a radio station, try connecting a permanent capacitor with a capacity of about 200 pF between the antenna and the receiver (Fig. P-7, a). You will notice that the receiver setting has changed, and to get the same volume you will have to turn the trimmer capacitor knob towards higher capacitance.

Now select capacitors with a capacity of 150, 100, 51 pF and connect them as an additional capacitor. It is easy to see that in each case it is necessary to further increase the capacitance of the tuning capacitor. From this we can conclude that when a capacitor is connected between the antenna and the receiver, the tuning of the receiver changes towards shorter wavelengths. So, if previously the receiver was tuned to, say, a wave of 547 m, then when an additional capacitor with a capacity of 200 pF is turned on, it will be tuned to a wave of 500 m, and with a 150 pF capacitor - to a wave of 450 m. This property can be used to tune the receiver without changes in the number of coil turns.

But in order to tune the receiver to longer waves, you need to connect a constant one in parallel with the adjusted capacitor (Fig. P-7, 6). The larger its capacity, the more long-wave radio stations the receiver will receive.

The sound volume of the detector receiver is low, and each of you, of course, would like to increase it. One way is to replace the coil with another, better quality one. The fact is that the volume of the receiver largely depends on what kind of wire the coil is wound with. The thicker the wire, the greater the volume you can get. Naturally, the dimensions of the coil will also change - the frame for it should now have a diameter of 60... ...80 mm and a length of 120...150 mm (Fig. P-8). Wind 150 turns of PEL or PEV wire with a diameter of 0.6...0.7 mm onto the frame. When winding, make taps from the 25th, 50th, 75th turns, counting from the bottom terminal in the diagram (“grounded”). Make the bends in the form of loops, which are then cleaned with a razor blade or sandpaper and tinned. During the experiment, connect the “grounded” terminal of capacitor C1 to these taps (Fig. P-9). To do this, solder a conductor to the capacitor and solder it to one or another tap. You can do it another way: put an alligator clip under the end of the conductor and connect it to the terminals. The fewer turns are connected between the antenna and the conductor (or alligator clip), the shorter the waves the detector receiver will receive. Naturally, during the experiment the old receiver coil will have to be disconnected and a new one connected in its place. The coil itself can be located on the table next to the receiver board. In this case, tuning to the radio station is done with a tuning capacitor - first when the coil is fully turned on, and then after each tap switch. Don't forget about the ferrite rod: by inserting it inside the frame, you can achieve smoother tuning to the radio station.

Having assembled the first detector receiver and carried out experiments with it, you quickly became acquainted with the action of a ferrite rod. It is made of a material with very high magnetic properties. Such a rod can be found in any small-sized transistor receiver. It makes it possible to significantly reduce the size of the inductor coil and at the same time obtain a coil of higher quality compared to a conventional one (even wound with thick wire, as was the case in the last experiment with the detector receiver), without a rod. Using a ferrite rod, you can build a miniature detector receiver that allows you to receive several broadcast radio stations (with a good outdoor antenna and grounding, of course).

The diagram of the tiny detector receiver is shown in Fig. R-10. It is similar to the circuit of the previous receiver, with the exception of two parts: the inductor and capacitor C1. Next to the symbol of the coil, a straight line appeared along its turns. This is the designation for the ferrite rod on which the coil turns are wound. As for the capacitor, it is of variable capacity, although an adjustable one can also be used.

To build this receiver, first of all, purchase a small-sized variable capacitor. This could be, for example, a KP-180 capacitor, the maximum capacitance of which is 180 pF, and the minimum is 5 pF. Take capacitor C2 type PM-1, K40P-2, KSO-2 or another, with a capacity of 2000 to 6800 pF. The diode is the same as in the previous receiver.

Wind the inductor on a piece of ferrite rod about 35 mm long. There is no rod of this length on sale, so you will have to take a long rod and break off the desired section from it. They do it like this. Wrap the rod in cloth and clamp it in a vice so that part of the rod of the required length protrudes on top. Now a sharp blow with a hammer on the protruding part is enough, and it will break off. The sharp edges of the rod at the chip site are ground off with a file.

Wind the winding (it takes up about 20 mm on the rod) with PEV or PEL wire with a diameter of 0.1 7...0.2 mm. In total you need to lay 100 turns. Secure the beginning of the winding to the rod with glue or several turns of wire laid on top of the first turn. First, wind turn to turn at the specified length, and then continue winding over the turns of the first layer, but lay the turns as evenly and as closely as possible to each other. The end of the winding can also be secured with glue or a small piece of adhesive tape.

The next stage is making the board. Cut it out of getinax, textolite or other insulating material. As in the previous receiver, install mounting studs on the board - there should be four of them. Attach the coil rod to the board between two brackets made of thick wire. Attach the variable capacitor to the board with two screws through the holes in the board from below.

Solder the parts to the studs, as shown in Fig. R-11.

To give your receiver a finished look, consider making its case. This could be, for example, a box measuring 45X60X20 mm, glued together from thin plexiglass or plywood. It is better to make the base of the box removable in the form of a lid, then it will be easy to insert a board inside the box and connect it to the sockets and connector (install these parts on the side walls of the box). In this case, take the connecting conductors of the same thickness as the studs—this will eliminate the need to attach the board to the case.

Install the board so that the axis of the variable capacitor passes through the hole in the top wall of the case. Attach the adjustment knob to the axis (it is included in the kit of the KP-180 capacitor) with a countersunk screw.

The receiver does not require any setup and is ready for use immediately after connecting the antenna, grounding and headphones. Although with the given coil data the receiver operates in the medium wave range (500...300 m), it is not difficult to switch it to the long wave range. To do this, wind 250...300 turns of PEV or PEL wire with a diameter of 0.1-7...0.2 mm onto a ferrite rod (at a length of 20 mm).

Is it possible to assemble a radio receiver consisting of less than 10 parts? Can this radio work without batteries?
Of course, this can be done quite simply: detector radio receivers are not at all complicated and can operate without batteries, receiving electricity from radio waves. In this article I will tell you how you can collect DIY radio that works without batteries, spending no more than an hour on the whole process!

What is good about a detector radio?
Firstly, this radio receiver works without batteries. Secondly, all the parts necessary for its assembly cost about 10-15 rubles, and there are plenty of them in old household electrical appliances. Thirdly, anyone can assemble a detector radio receiver, regardless of existing skills (reading and soldering iron skills are welcome)
But there are also disadvantages. Most likely, only one radio station that has the strongest signal in your area will have good reception. The second drawback is low power. It will be enough to give more or less normal sound from a small earphone, nothing more.
But still, such a receiver can be useful in the country when there are power outages or it is difficult to buy batteries.

So let's start collecting radio operating without batteries!
Do we need it for assembly?
Constant capacitor 190-500 Pf
Capacitor 1000-2000 Pf
Any diode (except light)
Copper wire with a diameter of 1-0.1 mm
A cylinder with a diameter of 10 cm (for example, a coffee can)
Newspaper
Metal peg about 30 cm long for grounding
A small speaker, for example from old headphones (radio phones)

This is what the Oganov detector radio receiver circuit looks like:

Let's start with the simplest thing - grounding. We drive the previously prepared metal peg into the ground, having first secured the wire to it (for safety reasons, it is better not to use the heating battery as grounding). And remember, the better the grounding, the better the reception of your radio will be. It is advisable to install grounding on the side of the house where the sun gets the least amount of light, where the ground is always damp. We carry the free end of the grounding wire into the house and attach it to the corresponding terminal of the radio receiver.

Then we create the antenna. I have it under the roof, about 10-12 meters long. It can be made from copper wire. Practice shows that with an antenna 10 m long, only one station will be received, but loudly. With an antenna length of 1-3 m, other stations can be received, but they will be very hard to hear.
Next we assemble the coil. The coil consists of two equal parts, 20 turns each (this is for receiving medium waves, and to receive long waves you need to wind 60 turns). How to assemble a reel? Let's take something round with a diameter of about 10 cm (for example, a beer can), cover it with a double layer of paper. The first layer is secured to the can with tape, the second is screwed onto the first. In this case, the coil will be easy to remove after winding. Now we carefully wind the copper wire - turn to turn. Between the two parts of the coil we leave 5 centimeters of wire, and also do not forget to leave about the same amount of wire at the beginning and end. After you have wound the coil, you need to wrap it with electrical tape in two layers along the turns. And after removing it from the can, wrap it crosswise as well. That's it, we won't need the newspaper anymore, we can get rid of it!

We begin assembling a radio receiver that works without batteries!
The diagram above can be simplified to the following form:

In this form it is easiest to assemble, and there will be fewer wires.
Carefully clean all the parts and solder them to each other according to the diagram! We attach the coil, antenna, grounding, earphone and, if you did everything correctly, we enjoy good and high-quality reception of the signal caught by our radio
If you want to tune to a different frequency, or the reception quality does not suit you, assemble a coil of thicker wire.
The adjustment is made by moving one part of the coil relative to the other. For more precise tuning, you can take several variable capacitors that replace C1, by tuning them you can tune in to the station as accurately as possible.
What your radio will look like depends entirely on your imagination! Due to its small size, the receiver can be packed into any container.
I hope that this article will be useful to someone.

To receive a local radio station, you can assemble a simple detector receiver. And when using a small radio component - transistor you can amplify the signal tens or hundreds of times. The transistor consumes very little energy and is capable of operating even at a voltage of about 1 V!

Radio receiver circuit

The circuit of the receiver described below contains only one transistor (see figure). The thing is that the headphones are in the collector circuit. In this mode, the transistor provides greater signal amplification.

On a common ferrite rod there are two inductance coils - loop inductor L1 (with variable capacitor C1 it forms the already known oscillatory circuit) and communication coil L2. The number of turns of the coupling coil is significantly less than that of the loop coil, and only part of the received signal is received by the transistor. This is done so that the transistor does not affect the oscillatory circuit and thereby does not change its settings.

So, from the coupling coil the signal goes to the base of the transistor through capacitor C2. Here it is detected, that is, an audio frequency signal is extracted from it, which is then amplified by a transistor and sent to headphones.

Bias is applied to the base of the transistor through resistor R1. In the diagram, you see an “asterisk” next to the letter designation of the resistor. It shows that this resistor may have to be selected (that is, its resistance must be specified) when setting up the receiver. This will be discussed later.

Receiver installation

The coils are wound on a ferrite rod with a diameter of 8 mm and a length of 40 - 50 mm. Coil L1 contains 80 turns, and L2 - 20 turns of PEL or PEV wire with a diameter of 0.15 - 0.2 mm. The distance between the windings is about 5 mm, the winding is turn to turn.

Mount some of the receiver parts on a board (see figure) made of insulating material, which resembles a detector receiver board. After installation, check the correctness of all connections and only then connect the power supply, headphones, antenna and grounding to the board racks (see figure). Using the switch, apply power to the receiver (a click should be heard in the headphones) and immediately measure the voltage between the emitter and the collector of the transistor - connect the positive probe of the voltmeter to the emitter circuit, and the negative probe to the collector circuit.

Receiver setup

The voltmeter needle should show a voltage of about 4.5 V. If it differs significantly (by more than 20%) from the indicated one, select resistor R1 - install another one instead (with lower or higher resistance).

It is not difficult to find out which resistor is needed. If the measured voltage is lower, you need to install a resistor with a higher resistance than that indicated in the diagram (for example, 390 kOhm, 430 kOhm, 470 kOhm, etc.). Conversely, if the measured voltage exceeds the specified value, the resistor resistance should be reduced (install a resistor with a resistance of 300 kOhm, 270 kOhm, 240 kOhm). You can do it differently (see figure) - instead of resistor R1, connect two resistors connected in series: a constant resistor with a resistance of about 100 kOhm and a variable resistor (of any type, for example SP-1, SPO-0.5) with a resistance of -4 MOhm. By moving the variable resistor slider, achieve the desired voltage, measure the resulting total resistance (the circuit must be unsoldered from the board) and install a constant resistor with approximately the same resistance on the board. In practice, such an adjustment rarely has to be done, since the required current transfer coefficient of the transistor is specified (60 - 100), and when using a transistor with this parameter, the bias resistor indicated in the diagram ensures the desired mode of its operation. All of the above is true, of course, only when using a fresh battery. Therefore, measure its voltage with the receiver connected (in other words, under load) - it should not be lower than 8.5 V, otherwise the battery will have to be replaced.

After checking and setting the voltage on the collector, touch the transistor base terminal with tweezers (or just your finger). There should be a faint hum in the phones - an alternating current background. If the base is not touched, a slight noise should be heard in the phones, indicating normal operation of the transistor.

Now you can check how many radio stations and at what volume the homemade product you installed is receiving. If you notice that the sound in the phones is distorted, unwind one or two turns from the L2 communication coil. If the sound volume is excessive, connect a small permanent capacitor (10 - 15 pF) between the external antenna and the antenna socket of the receiver. In any case, you can change the operating range of the receiver using the same means as for the previous design.

Mount the board and parts that do not fit on it (sockets, connector, switch and battery) in a housing, which can be structurally the same as for the detector receiver. The power conductors can be soldered directly to the battery terminals or used to connect the battery to the receiver using a connector block from a worn-out Krona.

B.S. Ivanov, Electronic homemade products.

P O P U L A R N O E:

Anyone who has an old broken TV sitting idle, this article may be useful. TVs usually have wideband speakers ranging from 3 to 10 W. Today we will use them to make small acoustic systems - satellites. A satellite is a small speaker (up to 20 cm in height) that plays mid and high frequencies.

You will need just one chip to build a simple and complete FM receiver that is capable of receiving radio stations in the range of 75-120 MHz. The FM receiver contains a minimum of parts, and its configuration, 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 microcircuit, which can be bought without problems on our favorite Ali Express.

Receiver circuit

FM Receiver Board

Placing elements on the board

Receiver setup

Conclusion