The VHF receiver operates in the range 64 - 108 MHz and has a sensitivity of no worse than 5 µV/m. Rated voltage - 3 V. The entire high-frequency path, including the FM detector, UHF and local oscillator, is assembled on one specialized DA1 type K174XA34. This microcircuit is a UHF, mixer, local oscillator, amplifier, amplifier-limiter, FM detector, noise reduction and frequency deviation compression systems, which allows the use of a low intermediate frequency - 60-80 kHz. The principle of the receiver is shown in the figure below:
The signal from the antenna is supplied to the UHF through capacitor C1. The local oscillator tuning frequency is determined by elements L1, C4, C5, VD1. Setting at the station is carried out by resistor R1, which changes the voltage on the KB109 type varicap VD1.
Active RC filters on operational amplifiers are used as PPFs, the external elements of which are capacitors C6, C8, C9, C11, C12 and C13. The audio frequency signal through capacitor C16 arrives at the volume - resistor R3. The U3Ch of the receiver can be anything, including the K174XA10. Fixed resistors type MLT-0.125. The L1 coil is frameless with an internal diameter of 3 mm. It has 7 turns of PEV 0.31 wire.
Tuning consists of setting the range by adjusting capacitor C4.
The receiver uses two specialized K174 series microcircuits. K174PS1 is a mixer and local oscillator, and K174XA10 includes an IF path, a detector, and an ultrasonic amplifier.
The receiver operates at a fixed frequency in the range 27 - 29 MHz. The sensitivity of the receiver at a signal-to-noise ratio of 12 dB is about 1 µV/m. Adjacent channel selectivity is 32 dB and depends on the parameters of the piezoceramic filter used. Selectivity in the mirror channel is 26 dB. Audio frequency power - 100 mW into a load with a resistance of 8 ohms. The receiver operates with a supply voltage of 4 to 9 V. The principle of the radio receiver is shown in the figure below:
The signal from the antenna goes to the base of transistor VT1, which acts as a balun. Circuit L1, NW determines the selectivity of the receiver along the mirror channel. The amplified signal is supplied to the input of a frequency converter made on K174PS1, the frequency of which is stabilized by ZQ1 quartz. From the converter load, the intermediate frequency signal is fed to the ZQ2 piezoceramic filter, which selects an intermediate frequency of 465 kHz from a set of frequencies. The IF signal is supplied to input 2 of the DA1 chip. The output stage of the amplifier is connected according to a non-standard circuit; the role of the load of the amplifier is performed by resistor R8. This somewhat degrades the quality of detection, but allows you to abandon the use of IF circuits and their settings. From the output of the detector, audio frequency voltage is supplied to the volume of R10 and from it to the power input of this microcircuit. From the ultrasonic output, the signal through capacitor C13 goes to the load - a loudspeaker or headphones.
All resistances in the circuit are MLT-0.125 type, resistor R10 is SP1 type. Coil L1 is wound on a ferrite rod with a diameter of 2.8 mm and a length of 14 mm and contains 16 turns of 0.23 mm PEV wire.
Resistor R8 is selected to minimize audio distortion with a minimum noise level at the ultrasonic sound output. Circuit L1, NW is tuned to the frequency of the high-frequency signal.
Description of the K174PS1 microcircuit can be
The circuit of a simple radio receiver on the K174XA10 integrated circuit is shown in the figure below:
The K174XA10 multifunctional microcircuit contains high frequency and low frequency. direct amplification, shown in the diagram, is equipped with an automatic AGC control system and a volume control.
The printed circuit board with the elements placed on it is shown in the figure below:
A VHF (FM) radio receiver assembled on a specialized KXA 058 microcircuit is shown in the figure below:
This circuit runs on just one 1.5 V battery. An ordinary earphone with a total impedance of 64 Ohms is used as an audio playback device. The battery power passes through the headphone jack, so you just need to pull the headphones out of the jack to turn off the receiver. The sensitivity of the receiver is sufficient that several high-quality HF and DV stations can be used on a 2-meter wire antenna.
Coil L1 is made on a ferrite core 100 mm long. The winding consists of 220 turns of PELSHO 0.15-0.2 wire. Winding is carried out in bulk on a paper sleeve 40 mm long. The tap must be made from 50 turns from the grounded end.
Receiver circuit with just one field-effect transistor
This version of the circuit of a simple single-transistor FM receiver works on the principle of a super-regenerator.
The input coil consists of seven turns of copper wire with a cross-section of 0.2 mm, wound on a 5 mm mandrel with a tap from the 2nd, and the second inductance contains 30 turns of 0.2 mm wire. The antenna is a standard telescopic one, powered by one Krona type battery, the current consumption is only 5 mA, so it will last for a long time. Tuning to a radio station is carried out by a variable capacitor. The sound at the output of the circuit is weak, so almost any homemade ULF will be suitable to amplify the signal.
The main advantage of this scheme in comparison with other types of receivers is the absence of any generators and therefore there is no high-frequency radiation in the receiving antenna.
The radio wave signal is received by the receiver antenna and is isolated by a resonant circuit on inductance L1 and capacitance C2 and then goes to the detector diode and is amplified.
FM receiver circuit using a transistor and LM386. |
I present to your attention a selection of simple FM receiver circuits for the range 87.5 to 108 MHz. These circuits are quite simple to repeat, even for beginner radio amateurs, they are not large in size and can easily fit in your pocket.
Despite their simplicity, the circuits have high selectivity and a good signal-to-noise ratio and are quite enough for comfortable listening to radio stations
The basis of all these amateur radio circuits are specialized microcircuits such as: TDA7000, TDA7001, 174XA42 and others.
The receiver is designed to receive telegraph and telephone signals from amateur radio stations operating in the 40-meter range. The path is built according to a superheterodyne circuit with one frequency conversion. The receiver circuit is designed in such a way that a widely available element base is used, mainly transistors of the KT3102 type and 1N4148 diodes.
The input signal from the antenna system is fed to the input bandpass filter on two circuits T2-C13-C14 and TZ-C17-C15. The connection between the circuits is capacitor C16. This filter selects the signal within the range of 7 ... 7.1 MHz. If you want to work in a different range, you can adjust the circuit accordingly by replacing transformer coils and capacitors.
From the secondary winding of the HF transformer TZ, the primary winding of which is the second filter element, the signal goes to the amplifier stage on transistor VT4. The frequency converter is made using diodes VD4-VD7 in a ring circuit. The input signal is supplied to the primary winding of transformer T4, and the smooth range generator signal is supplied to the primary winding of transformer T6. The smooth range generator (VFO) is made using transistors VT1-VT3. The generator itself is assembled on transistor VT1. The generation frequency lies in the range of 2.085-2.185 MHz, this range is set by a loop system consisting of inductance L1, and a branched capacitive component of C8, C7, C6, C5, SZ, VD3.
Adjustment within the above limits is carried out by variable resistor R2, which is the tuning element. It regulates the constant voltage on the VD3 varicap, which is part of the circuit. The tuning voltage is stabilized using a zener diode VD1 and a diode VD2. During the installation process, overlap in the above frequency range is established by adjusting the capacitors SZ and Sb. If you want to work in a different range or with a different intermediate frequency, a corresponding restructuring of the GPA circuit is required. It’s not difficult to do this armed with a digital frequency meter.
The circuit is connected between the base and emitter (common minus) of transistor VT1. The PIC required to excite the generator is taken from a capacitive transformer between the base and emitter of the transistor, consisting of capacitors C9 and SY. RF is released at the emitter VT1 and goes to the amplifier-buffer stage on transistors VT2 and VT3.
The load is on the HF transformer T1. From its secondary winding, the GPA signal is supplied to the frequency converter. The intermediate frequency path is made using transistors VT5-VT7. The output impedance of the converter is low, so the first stage of the amplifier is made using a VT5 transistor according to a common-base circuit. From its collector, the amplified IF voltage is supplied to a three-section quartz filter at a frequency of 4.915 MHz. If there are no resonators for this frequency, you can use others, for example, at 4.43 MHz (from video equipment), but this will require changing the settings of the VFO and the quartz filter itself. The quartz filter here is unusual; it differs in that its bandwidth can be adjusted.
Receiver circuit. The adjustment is carried out by changing the containers connected between the filter sections and the common minus. For this, varicaps VD8 and VD9 are used. Their capacitances are regulated using a variable resistor R19, which changes the reverse DC voltage across them. The filter output is to the T7 RF transformer, and from it to the second stage of the amplifier, also with a common base. The demodulator is made on T9 and diodes VD10 and VD11. The reference frequency signal comes to it from the generator at VT8. It should have a quartz resonator the same as in a quartz filter. The low-frequency amplifier is made using VT9-VT11 transistors. The circuit is two-stage with a push-pull output stage. Resistor R33 regulates the volume.
The load can be both the speaker and headphones. Coils and transformers are wound on ferrite rings. For T1-T7, rings with an outer diameter of 10 mm are used (imported type T37 is possible). T1 - 1-2=16 vit., 3-4=8 vit., T2 - 1-2=3 vit., 3-4=30 vit., TZ - 1-2=30 vit., 3-4= 7 vit., T7 -1-2=15 vit., 3-4=3 vit. T4, TB, T9 - 10 turns of wire folded in three, solder the ends according to the numbers on the diagram. T5, T8 - 10 turns of wire folded in half, solder the ends according to the numbers on the diagram. L1, L2 - on rings with a diameter of 13 mm (imported type T50 is possible), - 44 turns. For all, you can use PEV wire 0.15-0.25 L3 and L4 - ready-made chokes 39 and 4.7 μH, respectively. KT3102E transistors can be replaced with other KT3102 or KT315. Transistor KT3107 - on KT361, but it is necessary that VT10 and VT11 have the same letter indices. 1N4148 diodes can be replaced with KD503. The installation was carried out in a three-dimensional manner on a piece of foil fiberglass laminate measuring 220x90 mm.
This article provides a description of three simple receivers with a fixed tuning to one of the local stations in the MF or LW range; these are extremely simplified receivers powered by a Krona battery, located in subscriber speaker housings containing a speaker and a transformer.
The schematic diagram of the receiver is shown in Figure 1A. Its input circuit is formed by coil L1, capacitor cl and an antenna connected to them. The circuit is tuned to a station by changing capacitance C1 or inductance Ll. The RF signal voltage from part of the coil turns is supplied to the diode VD1, which works as a detector. From variable resistor 81, which is the load of the detector and the volume control, low frequency voltage is supplied to the base VT1 for amplification. The negative bias voltage at the base of this transistor is created by the constant component of the detected signal. Transistor VT2 of the second stage of the low-frequency amplifier has a direct connection with the first stage.
The low-frequency oscillations amplified by it pass through the output transformer T1 to loudspeaker B1 and are converted into acoustic oscillations. The receiver circuit of the second option is shown in the figure. The receiver assembled according to this circuit differs from the first option only in that its low-frequency amplifier uses transistors of different conductivity types. Figure 1B shows a diagram of the third version of the receiver. Its distinctive feature is positive feedback carried out using the L2 coil, which significantly increases the sensitivity and selectivity of the receiver.
To power any receiver, a battery with a voltage of -9V is used, for example, “Krona” or made up of two 3336JI batteries or individual elements; it is important that there is enough space in the subscriber speaker housing in which the receiver is assembled. While there is no signal at the input, both transistors are almost closed and the current consumption of the receiver in rest mode does not exceed 0.2 Ma. The maximum current at the highest volume is 8-12 Ma. The antenna is any wire about five meters long, and the grounding is a pin driven into the ground. When choosing a receiver circuit, you need to take into account local conditions.
At a distance of about 100 km to the radio station, using the above antenna and grounding, loud-speaking reception by receivers is possible according to the first two options, up to 200 km - the scheme of the third option. If the distance to the station is no more than 30 km, you can get by with an antenna in the form of a wire 2 meters long and without grounding. The receivers are mounted by volumetric installation in the housings of subscriber loudspeakers. Remaking the loudspeaker comes down to installing a new volume control resistor combined with the power switch and installing sockets for the antenna and grounding, while the isolation transformer is used as T1.
Receiver circuit. The input circuit coil is wound on a piece of ferite rod with a diameter of 6 mm and a length of 80 mm. The coil is wound on a cardboard frame so that it can move along the rod with some friction. To receive DV radio stations, the coil must contain 350, with a tap from the middle, turns of PEV-2-0.12 wire. To operate in the CB range there must be 120 turns with a tap from the middle of the same wire; the feedback coil for the receiver of the third option is wound on a contour coil, it contains 8-15 turns. Transistors must be selected with a gain Vst of at least 50.
Transistors can be any germanium low-frequency of the appropriate structure. The transistor of the first stage must have the minimum possible reverse collector current. The role of a detector can be performed by any diode of the D18, D20, GD507 and other high-frequency series. The variable volume control resistor can be of any type, with a switch, with a resistance from 50 to 200 kilo-ohms. It is also possible to use a standard resistor of the subscriber loudspeaker; usually resistors with a resistance of 68 to 100 kohms are used. In this case, you will have to provide a separate power switch. A trimmer ceramic capacitor KPK-2 was used as a loop capacitor.
Receiver circuit. It is possible to use a variable capacitor with a solid or air dielectric. In this case, you can insert a tuning knob into the receiver, and if the capacitor has a sufficiently large overlap (in a two-section, you can connect two sections in parallel, the maximum capacity will double) you can receive stations in the LW and SW range with one medium-wave coil. Before tuning, you need to measure the current consumption from the power source with the antenna disconnected, and if it is more than one milliampere, replace the first transistor with a transistor with a lower reverse collector current. Then you need to connect the antenna and by rotating the rotor of the loop capacitor and moving the coil along the rod, tune the receiver to one of the powerful stations.
Converter for receiving signals in the 50 MHz range The IF-LF transceiver path is intended for use in the latter, superheterodyne circuit, with single frequency conversion. The intermediate frequency is chosen to be 4.43 MHz (quartz from video equipment is used)
Magnetic ferrite antennas are good for their small size and well-defined directivity. The antenna rod should be positioned horizontally and perpendicular to the direction of the radio. In other words, the antenna does not receive signals from the ends of the rod. In addition, they are insensitive to electrical interference, which is especially valuable in large cities, where the level of such interference is high.
The main elements of a magnetic antenna, designated in the diagrams by the letters MA or WA, are an inductor coil wound on a frame made of insulating material, and a core made of high-frequency ferromagnetic material (ferrite) with high magnetic permeability.
Receiver circuit. Non-standard detector |
Its circuit differs from the classical one, first of all, in a detector built on two diodes and a coupling capacitor, which allows you to select the optimal circuit load for the detector, and thereby obtain maximum sensitivity. With a further decrease in capacitance C3, the resonance curve of the circuit becomes even sharper, i.e., the selectivity increases, but the sensitivity decreases somewhat. The oscillating circuit itself consists of a coil and a variable capacitor. The inductance of the coil can also be varied within wide limits by moving the ferrite rod in and out.
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
Here is the receiver circuit itself. Two more microcircuits were added to it, so that in the end it turned out to be a completely finished device. Let's start looking at the diagram from right to left. The now classic low-frequency amplifier for a small dynamic head is assembled using the LM386 chip. Here, I think, everything is clear. A variable resistor adjusts the volume of the receiver. Next, a 7805 stabilizer is added above, which converts and stabilizes the supply voltage to 5 V. Which is needed to power the microcircuit of the receiver itself. And finally, the receiver itself is built on the TDA7000. Both coils contain 4.5 turns of PEV-2 0.5 wire 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 using a variable resistor. The voltage from which 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 with 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.Placing elements on the board
Used classic LUT technology to produce the board.
I printed it, heated it 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 hissing in the dynamic head. This means that everything is working fine for now. The whole setup comes down to setting up the circuit and selecting the range for reception. I make adjustments by rotating the coil core. Once the reception range is configured, channels in it can be searched for using a variable resistor.Conclusion
The microcircuit has good sensitivity, and a half-meter piece of wire, instead of an antenna, can pick up a large number of radio stations. The sound is clear, without distortion. This circuit can be used in a simple radio station, instead of a receiver on a supergenerative detector.Now we will make a real FM Radio based on two cheap chips TDA7000 and LM386. What is TDA7000 and how does it work. This is a real FM receiver, with a conventional local oscillator, mixer, limiting amplifier, and phase detector. The microcircuit also has automatic frequency control. But the noise reduction function is somewhat weak, to say the least. If necessary, connecting a 10K resistor from the power supply to pin 1 will disable the squelch.
Block diagram of the microcircuit
Block diagram of TDA7000 is used as for a normal FM receiver. Audio output is about 75 mV. For more details, see the documentation for 7000.
Before soldering the circuit, we strongly recommend that you look into the . It gives a good idea of the operation and usage of the chip. Please note that the TDA7000 is not suitable for receiving part in a stereo decoder. This is the price for simplicity and quality. If stereo is fundamental - .
Schematic parts list
Chip IC1 TDA7000 FM Radio
Chip IC2 LM386 Audio amplifier
18-pin connector (for TDA7000)
8-pin connector (for LM386)
Ceramic capacitors:
0.001 uF x 1 pcs
0.01uF x 1 piece
0.1 uF x 4 pcs
0.0022 uF x 1 piece
0.0033 uF x 2 pcs
0.022 uF x 1 piece
150 pF x 1 piece
180 pF x 2 pcs
220 pF x 2 pcs
330 pF x 2 pcs
Electrolytic capacitors:
220µF or 470µF or 1000µF - x 2 pcs
4.7µF - X 1 piece
Other radioelements:
10K (or 20 kOhm) trim resistor
C1 - Ceramics
L1 - Adjustable coils for tuning radio stations
10 ohms 1/4W or 1/6 W x 1 pcs
22K, 1/4 or 1/6 W x 1 piece
Speaker 8 Ohm 1 Watt
9V battery power
By the way, Philips did not stop at the TDA7000 in its 18-pin DIP package. Next came the TDA7010T which is the surface mount version. It comes in 16-pin SMD form. Next comes the TDA7021T chip, which is also designed for surface mounting, but is already stereo compatible with the decoder. And finally, there is the TDA7088T, which is mono only, but has automatic tuning search and operates on just 3V power. Unfortunately, the TDA7000 is no longer in production, having been discontinued in December 2003. Although they were produced for quite a long time - a little over 20 years.
Assembling a radio receiver on a TDA7000 chip
Together with the TDA7000, you can use the LM386 bass amplifier for the audio channel. At first a transistor amplifier was made, but the chip has a higher gain. Now the sound is very good.
We highly recommend this chip, where simplicity of circuit design is combined with high sound quality. Despite its ease of use, this is an excellent FM receiver.
VHF-FM receiver
This module can be built, for example, into an active computer speaker system, or an old AM receiver, even a tube radio, so that you can receive VHF-FM radio broadcast signals in the range of 87-108 MHz. The module is made on the TDA7088T chip, its main advantage is that setting up the receiver is extremely simple, you don’t even need any equipment. Just roughly set the range by adjusting the heterodyne coil, focusing on the reception of all local stations, and adjust the input circuit setting so that the sensitivity is greatest. Another advantage of the TDA7088T is its two-button electronic configuration. Disadvantage - there is no scale. All this allows you to embed the receiver anywhere where there is the necessary power and ULF. And also a place for the board. Buttons can be either on the board or remote.
The schematic diagram of the module is shown in Figure 1.
Figure 2 shows a drawing of the printed circuit board and wiring diagram. The microcircuit is located on the side of the printed conductors, and all the parts are on the other side.
The W1 antenna can be anything, either a telescopic rod or a piece of mounting wire. The input circuit is coil L1 and capacitors C1 and C2. The RF input is symmetrical and high-impedance, so the coil does not have a coupling coil or taps. Resistor R1 limits the input impedance of the antenna input. The input circuit is set to the middle of the range and is not adjusted when tuning across the range.
Heterodyne circuit on coil L2, capacitor C4 and varicap VD1. The tuning voltage for the varicap comes from pin 15 of the microcircuit. Settings are made using two buttons S1 and S2. When you press S2, the radio station is automatically searched. When pressed again, searches and moves to the next radio station. And so on until the end of the range. You can then return to the beginning of the range by pressing the S2 button. And repeat the setting again with the S1 button. This setup has an important advantage: you only need to install two buttons on the device panel. It is very simple and does not damage the device. But there is also a drawback - the lack of a setting scale.
The low-frequency output voltage is only 100 mV, which is not enough for the inputs of most equipment, so an additional ULF cascade on transistor VT1 is installed in the circuit. If the AF output voltage of 100 mV is sufficient, you can dispense with the cascade on VT1, and remove the low-frequency signal from pin 2 of the microcircuit.
Supply voltage from 3 to 6V. That is, from two to four galvanic cells. If the supply voltage of the device where the module is installed is higher, you can lower it with an integrated stabilizer, for example, 78L05.
Coils L1 and L2 are frameless. Inner diameter 3 mm. L1 - 7 turns, L2 - 9 turns. Wire PEV 0.43. Adjustment of coils by stretching and squeezing. After tuning, it is advisable to fix the heterodyne coil with a drop of paraffin, otherwise it may become microphonic.
Privalov Yu.
