VHF receiver on one chip. Stationary VHF-FM radio receiver from modules from old TVs
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In the last decade, VHF receivers have been widely and ubiquitously used. This is due to the constantly growing number of radio stations in various directions, as well as the high sound quality of FM receivers compared to AM and the possibility of stereo sound. However, in the post-Soviet space there are a number of problems with the quality of commercially available radios and their use in large cities, in the presence of a large number radio stations and difficult electromagnetic environment. The author of this article considers the position of the Russian market of VHF radio receivers, their shortcomings and options for solving these problems. All this is characteristic not only of Russia, but will be true in Belarus as well.
A look at the Russian market
Classifying household receivers according to consumer functions, one can see that the domestic market contains:
- battery powered miniature receivers;
- small stationary devices with mains/combined power supply;
- VHF receivers as part of music centers;
- car radios and car receivers.
But you will not find domestic household VHF receivers, with the possible exception of car radios of the Ural family. Why? The answer seems to be obvious - in the area portable devices, where the main thing is the minimum cost, you can’t compete with the products of the countries of the South-Eastern region (mainly China). There is no talk at all about music centers and car radios - the domestic industry has never been able to produce technologically sophisticated equipment for such a low price with high quality. In the same receivers of the Ural family, the mechanical components - both the tape drive mechanism and the CD player - are exclusively of imported origin. Stationary receivers with mains power, as it were, fell out of the circle of interests of manufacturers. What is available on the market today is either the same portable products with mains power, or VHF tuners as part of various devices(for example, alarm clocks) and music centers. The former, as a rule, have congenital functional deficiencies, the latter are quite high price. In addition, if desired, you can find a high-quality radio - but it will be multi-band. Does the mass consumer in the city need a long-medium-shortwave receiver today? After all, the quality of the received amplitude-modulated (AM) signal in these ranges is extremely low and cannot compete with the frequency-modulated (FM) VHF signal, especially in the city - due to both the properties of wave propagation and modulation features. And additional reception ranges in an expensive device are additional money paid for virtually nothing.
At the same time, in Russia the need for stationary VHF receivers may be even higher than in many other countries. In fact, even today a rare housewife in the kitchen (secretary in the office, saleswoman in the stall) does without a radio. And if there is not enough money for an expensive device, you have to use either radio broadcast receivers for wired broadcasting ("three-programmers"), or simple Chinese-made VHF receivers, at best - with the Panasonic brand. It is clear that radio broadcasting networks cannot compete with VHF stations - neither in the number of programs, nor in the quality of the transmitted signal. Therefore, VHF receivers - for summer cottages, for kitchens, even for work - will be sold in Russia for a long time to come. Suffice it to recall the size of the park of wire broadcasting receivers ("kitchen radio"), and the potential capacity of this consumer niche becomes clear. And here the national characteristics of this market may appear, providing a certain chance for domestic producers.
Features of the Russian air
What distinguishes the requirements for VHF receivers in Russia? Let's define that we are talking about inexpensive devices that use mains power and are designed for long-term listening. The latter means that the requirements for the quality of the reproduced signal are quite high - both in terms of the spectral composition and the presence of interference.
The first significant feature is that in Russia there are two VHF broadcasting bands: 65.8-74.0 and 88-108 MHz, Soviet and Western, respectively. And the differences here are not only in the actual frequency sections of the broadcast - the frequency grid pitch is different, respectively 30 and 100 kHz, as well as the frequency deviation of the FM signal - 50 and 75 kHz. Even the polarization of radio signals emitted by transmitters in the Soviet range is horizontal, and in the western range it is vertical!
In addition, our stereo coding standards are different than in the rest of the world. In stereo broadcasting, the FM signal is modulated with a so-called complex stereo signal (CSS). In the USSR, a system with a polar-modulated (PM) signal was adopted (standard of the International Organization of Radio Broadcasting and Television - OIRT). In this case, the audio signal modulates the subcarrier frequency of 31.25 kHz, but in such a way that the envelope of the positive half-cycles is modulated by the signal of the left stereo channel, and the negative half-cycles are modulated by the signal of the right one. The subcarrier is suppressed by 14 dB. In the standard of the International Advisory Committee for Radio Broadcasting (CCIR), adopted almost all over the world, the 38 kHz subcarrier is completely suppressed during the formation of the CCC, and a 19 kHz pilot tone is transmitted in the receiver to restore it (Fig. 1).
Fig.1. Formation of a complex stereo signal (a) and its representation in the OIRT (6) and CCIR (c) standards.
In addition, in Russia, in the conditions of megacities, there are additional problems associated with the location of transmission centers. For example, for Moscow, Ostankino, Oktyabrskoye Pole, Balashikha, Shabolovka is far from a complete list of transmitter geography. As a result, depending on the receiving point, the signal level on adjacent channels (with a spacing of about 300-400 kHz) can differ by tens of decibels, which imposes special requirements on the dynamic range and selectivity of receivers.
Anatomy of a VHF receiver
The classical scheme of the VHF receiver of the FM signal is shown in fig. 2. This is a single frequency conversion receiver (superheterodyne circuit). The signal from the antenna enters the high-frequency (HF) path, which includes a preselector (input band-pass filter and high-frequency amplifier - UHF), as well as a local oscillator with a mixer. UHF not only amplifies the signal, but also filters it in a given band. The amplified RF signal enters the mixer, which ideally implements the function U=u n cos(2n f n t)· u ub> G cos(2n f G t), where f n , u n and f G u G- frequency and amplitude of the input signal and the local oscillator signal, respectively. After the mixer, the signal (up to amplitude) has the form cos2p( f n +f G)t+cos2p( f n - f G)t, which corresponds to modulated carrier signals f n +f G and | f n -f G|. Difference component - intermediate frequency (IF) f pch =|f n -f G| - allocates with a band-pass filter and further work with it.
The IF signal is filtered and amplified, after which the signal will go to a frequency detector - an FM demodulator (frequency-to-voltage converter). After demodulation, the low-frequency signal is amplified to an audio frequency amplifier and then to playback devices. When broadcasting stereo programs, after the frequency detector, the signal first arrives at the stereo decoder. Of course, we have listed only the most basic functional blocks - without considering such important functions for a home receiver as automatic frequency control, noiseless tuning, comfort noise generation, automatic level control, etc. Tuning to the station frequency occurs by simultaneously changing the frequency of the local oscillator and the LC circuits of the preselector.
Fig.2. Generalized block diagram of a superheterodyne FM receiver.
In superheterodyne circuits, one of the main problems is the need to suppress the signal in the so-called mirror channel. Its nature is clear - since after the mixer, f pch =|f n -f G|, can get into the IF path as a signal with a frequency f n =f G -f pch(if the local oscillator frequency is higher than the tuning signal), and with f h =f G +f pch, i.e. a signal located symmetrically to the tuning frequency relative to the local oscillator frequency. Consequently, f h =f n±2 f pch depending on whether the desired signal is above or below the local oscillator frequency. It is clear that it is necessary to suppress the signal in the mirror channel in the preselector, before the mixer. Moreover, the higher the IF, the greater the separation of the main and mirror channels and the easier it is to solve this problem. But even for a standard 10.7 MHz IF, the mirror channel of the "Soviet" VHF range turns out to be in the 87.2-95.4 MHz region, where some television channels and their soundtrack are located in Russia, and now also radio stations of the western broadcasting range. The paper shows that in this case, the selectivity for the image channel should be at least no worse than 78 dB - and in some cases even as much as 100 dB. Whether it is possible to achieve such a high selectivity in household equipment is a big question.
Not less than important characteristic is the selectivity in the adjacent channel. And for VHF, the allowable separation of adjacent channels when broadcasting various programs from neighboring zones is only 180 kHz. Of course, in almost one zone it is 300-400 kHz. Adjacent channel selectivity is especially important for cities where broadcasting is carried out from several centers, and radio stations adjacent in frequency, but spaced apart in space, can induce signals in the antenna that differ in level by tens of decibels.
Fig.3. Construction of a UKB-receiver on a Philips IC kit.
Fig.4. Structural diagram of the TDA7021 IC.
However the main problem VHF receiver - the need to ensure its low cost, since technically all of the listed difficulties are completely solvable. In fact, this is the problem of all household appliances, and it is solved in a standard way - by the release of mass ICs, into which as many functional blocks of the device as possible are integrated. One of the first single-chip tuners was released by Philips back in 1983 - it was the famous TDA7000. The solutions embedded in it turned out to be so successful that it served as a prototype for many ICs - both direct analogues, for example, KS1066XA1, K174XA42, and more advanced circuits from Philips itself. These are ICs such as the TDA7021 with extended bandwidth for stereo reception, and the TDA7088, which includes a search engine and auto tuning to the station frequency. The main advantage of such schemes is the ease of implementation of the device with a minimum of additional components. An example of a completed receiver circuit on the TDA7021 with a stereo decoder (TDA7040T) and an amplifier (TDA7050T) is shown in Fig. 3. Note that for a miniature mono receiver, the last two ICs are not needed.
The downside of this by far the cheapest solution is the low IF, around 70kHz (typically 69-76kHz). Such a low IF made it possible to use active band-pass filters based on operational amplifiers that are part of the receiver IC (Fig. 4). But in this case, the mirror channel turns out to be less than 150 kHz away from the tuning frequency, therefore, there is no selectivity in the adjacent channel. The only thing that saves is that the broadcast channels are actually separated by 300-400 kHz. However, the interference from the image channel increases the noise figure of the receiver by at least 3 dB. It is clear that an increase in sensitivity at such a low selectivity will not lead to anything good. In addition, in the range of 88-108 MHz, the maximum deviation of ±75 kHz practically coincides with the IF, and in the path of such an IF, nonlinear distortions of the FM signal are inevitable. Therefore, a negative frequency feedback (SFN) is introduced into the circuit, which limits the frequency deviation of the received FM signal. Thanks to the SFN, not only the deviation is reduced to 15-20 kHz, but also the local oscillator tuning accuracy is improved - frequency auto-tuning is implemented. The SFN signal is formed by a limiting amplifier after the frequency demodulator, and it controls the tuning varicaps of the local oscillator (see Fig. 4). However, as the bandwidth of the signal decreases, its dynamic range decreases, and therefore the quality of the audio signal deteriorates. The inevitable distortions at the peaks of deviation also lead to a deterioration in perception. Since the same varicap is used in the IC both in the frequency-setting local oscillator circuit and in the frequency feedback loop, the local oscillator tuning slope is different at the beginning and end of the range, and, consequently, the level of the output low-frequency signal is also different. ICs of the TDA70xx family and their analogues are described many times and in detail (for example, in work). It is important for us to state that VHF receivers based on these ICs are unacceptable for Russian megacities, if we are not talking about toys.
Of course, all of these problems are well known, so many specialized ICs for radio equipment with a standard 10.7 MHz IF are produced. One of many examples is the TEA5711 stereo AM/FM receiver (Figure 5). The scheme of its inclusion is shown in Fig.6. This IC contains a stereo channel decoder - but in the CCIR standard. Philips also produces a VHF receiver IC without a stereo decoder - TEA5710. Actually, there are quite a lot of similar circuits (with and without a stereo decoder) today - they are produced by companies such as Sony (CXA1238 and 1538), Sanyo, Matsushita, Rohm, Toshiba, etc. (the element base of modern receivers is considered in more detail, for example, in the work) .
However, with all the diversity of the modern element base, almost all inexpensive models in Russia are represented by fairly similar Chinese-made receivers, at best with an IF of 10.7 MHz, supporting the ranges of 65.8-74 and 88-108 MHz, with tuning to the station by rotating vernier. As a rule, these are single-band receivers designed for a frequency interval of 65-108 MHz. As a result, the received frequencies are at the edges of their operating range. With such a large overlap, it is extremely difficult to ensure the coupling of the input filter and the frequency-setting local oscillator circuit - and the tuning is carried out by simultaneously tuning the variable capacitors in these LC circuits. They have a different overlap ratio and, as a rule, good pairing can be achieved at three points - at the edges and in the middle of the range, which leads to uneven receiver sensitivity over the range. In addition, such a large overlap with an uneven distribution of broadcast channels (at the edges) makes it extremely difficult to tune into a station - often the program is separated from the program by turning the tuning knob by fractions of a degree. It is clear that it is impossible to determine the frequency value on the tuning scale of such a radio receiver.
Fig.5. Block diagram of the TEA5711 stereo tuner IC.
In addition, the need for high noise immunity of the urban receiver imposes increased requirements on the accuracy of tuning all circuits - and there are several of them, and they contain high-quality inductors made as a separate element. Setting up these nodes does not fit well with the ideology of mass production through low-skilled personnel. As a result, almost all Chinese-made VHF receivers differ not only in rather primitive circuitry and ill-conceived design in terms of noise immunity. For the most part, their internal nodes are simply not configured - after all, the receiver somehow works somewhere, and how well the manufacturer is not interested.
What kind of receiver does Russia need?
A few years ago, employees of the Postamarket company asked this question, announcing, with the participation of the Ekho Moskvy radio station, a competition for the best VHF receiver solution for Russia. As mandatory requirements, work in two VHF bands was indicated, the possibility of digital tuning with memorization of at least 10 stations, indication of the tuning frequency, the presence of a socket for connecting an external television antenna, external mains power, confident operation in a complex electromagnetic environment of a metropolis, high manufacturability and low cost. Unfortunately, the organizers were presented with only one interesting solution from the development team of the Research Institute of RP - but it really met their difficult requirements. What is its essence? The developers decided to abandon classical scheme superheterodyne receiver with a single frequency conversion and proposed the generally known principle of infradyne reception, when the IF is significantly higher than the operating frequency range. This method sometimes used in expensive stationary AM receivers, but in the VHF band this approach seemed prohibitively expensive. However, the elemental base is developing, and what was exclusive yesterday, today turns out to be massive and inexpensive.
Fig.6. Wiring diagram for TEA5711 with ULF TDA7050T.
With the infradyne scheme, the preselector is made non-tunable and broadband - for the entire reception range, which greatly simplifies its design. True, the inevitable price for this is that the input circuits (filters, UHF, mixer) must have a wide dynamic range and high linearity. But this is already a circuitry problem, which can be completely solved with a modern element base. Tuning to the station is carried out exclusively by tuning the frequency of the first local oscillator.
The scheme proposed by the developers (see Fig. 7) uses two separate input band-pass filters for the ranges of 65.8-74 and 88-108 MHz and double frequency conversion. The first IF is 250 MHz, therefore, the frequency of the first local oscillator should be in the range of 315-360 MHz. Thus, the mirror channel turns out to be very far from the working one - above 565 MHz, and there are no problems with its suppression by the input filter.
Perhaps the key element of this receiver is the IF filter. Its frequency response should be almost rectangular, with a bandwidth of 250 kHz at a center frequency of 250 MHz. Having managed to decide this problem, the developers received a receiver with only one tunable element (the first local oscillator). After the IF filter, the signal is converted to the second IF - already standard, 10.7 MHz. In this case, the second local oscillator is tuned to a fixed frequency, and all further signal processing is implemented by standard elements of a well-developed and cheap 10.7 MHz IF path. In other words, the local oscillator frequency is fixed in a standard superheterodyne receiver, and instead of a tunable complex preselector, a broadband non-tunable preselector and a highly linear high-frequency path up to the first IF are introduced. This made it possible to solve the problems of selectivity in the mirror and adjacent channels and to prevent non-linear combination noise.
Fig.7. Functional diagram of an infrared ultrasonic receiver with a broadband preselector.
Note that until relatively recently, a significant problem was the lack of a stereo decoder IC that supports both the CCIR (pilot tone) and OIRT (PM) standards. However, it has disappeared since Angstrem began producing IC KR174XA51 - a stereo decoder with PLL synchronization, with automatic and forced determination of decoding standards (Fig. 8).
However, Angstrem produces an IC kit for a VHF receiver. But since this enterprise is focused on the market of the South-Eastern region, the KR174XA34 tuner IC produced by it is designed for low IF, about 70 kHz. Above, we talked about the lack of such tuners and their unsuitability for high-quality receivers, especially in Russia. However, the market for tuner ICs is quite large and there are plenty to choose from. For example, the Minsk NPO Integral produces ILA1238NS and ILA1191NS microcircuits - analogues of well-known ICs Sony CXA1238 and CXA 1191 (stereo and mono receivers rated for 10.7 MHz IF).
An extremely important aspect is receiver control. There are more than thirty radio stations in both VHF bands in Moscow, and not much less in other large cities. Therefore, digital tuning with a memorization of at least 10 stations and an indication of the receiving frequency is not a luxury, but a necessary requirement for a stationary receiver. But with today's variety of frequency synthesizers, indicators of all types and their controllers, as well as universal microcontrollers, there are no problems with an inexpensive implementation of this function - up to control via infrared. There is no digital tuning in cheap Chinese models, and this is another potential "plus" for domestic manufacturers. However, there are cheap Chinese VHF receivers with digital tuning. (As a rule, the tuning system works in them too, but not in the receiver itself.)
Thus, there are prerequisites for the production of a unique domestic receiver - a "kitchen VHF radio". First of all, inexpensive foreign models cannot cope with the difficult interference environment and broadcasting features in large Russian cities. In addition, they have a primitive, and therefore too inconvenient user interface. Finally, only expensive models fully support operation in two Russian VHF bands, especially in terms of stereo reception (but the inherent disadvantages of devices with a standard 10.7 MHz IF remain with them). At the same time, the implementation of all additional functions is a rather simple task compared to high-quality signal reception and does not significantly increase the cost of the product, especially in mass production. But the circuit of the tuner itself deserves the closest attention, and the concept of an infra-deep VHF receiver proposed and tested by the developers of the Research Institute of RP can become the very missing link that can connect high quality and a low price - unless, of course, someone offers more optimal solution.
What is not in Russia
The only thing that is not available in our country for mass VHF receivers is the possibility of manufacturing modern cases. After all, a radio receiver, like any household appliance, is not only a carrier of a technical function, but also an interior element, an object that should please the eye. And without a variety of high-quality cases, the most interesting and promising development will remain inside the breadboard box. Without solving the problem of producing high-quality plastic products, so seemingly far from electronics, the production of electronic household appliances in Russia is impossible. And this is a matter of investing money in the purchase of equipment and, most importantly, in mold development technology. One manufacturer probably can't afford it. Of course, cases (or molds) can be ordered in the same China - but, firstly, this is quite an expensive pleasure, and secondly, in this case it is extremely difficult to guarantee that these cases will be not only with their customer, but and from everyone who wants to buy them. to copyright and pirated copies they are treated in a very peculiar way - according to Western concepts. And protection from this is again a lot of money.
But maybe radio stations are interested in their programs reaching as many potential listeners as possible. And that the reception quality of their signal was high enough? So isn't it time in Russia to organize a consortium of developers, manufacturers of VHF equipment and broadcasting enterprises? Similar consortiums for the development of advanced technologies are common throughout the world. Although VHF broadcasting is not a new technology, but since in Russia there is a problem that is beyond the strength of one manufacturer, but many are potentially interested in solving, maybe the path of cooperation will bring results?
Sources
- Kononovich L.M. Modern broadcasting receiver - M .: Radio and communication, 1986.
- Polyakov V. Single-chip FM receivers. - Radio, 1997, No. 2.
- Kulikov G., Paramonov A. Radio receiving paths of household audio equipment (parts 1 and 2). - Repair of electronic equipment, 2000, No. 2-3.
VHF-FM radio receiver
Currently, there are many Chinese-made radios on sale, which, due to low sensitivity, do not work equally well everywhere. However, it is not at all difficult to make a radio receiver using ready-made blocks from old TVs. As practice shows, such receivers have a sufficiently high sensitivity, which is important for amateurs who live far from the location of the antennas of transmitting stations, especially in mountainous areas. It is convenient to use such "free" stationary receivers in garages, workshops, boat stations, etc.
In TV sets released in the CIS, the principle of obtaining an intermediate frequency of the sound was used as the difference between the frequencies of the image carrier and the sound carrier; which is equal to 6.5 MHz. On admission television signal at the output of the channel selector, after conversion, there are signals of intermediate frequencies of the image fpch = 38 MHz and the sound fchz-| = 31.5 MHz, from which the signal of the second intermediate sound (difference frequency) fpchz-|| = 6.5 MHz. It is clear that it is impossible to receive broadcast signals from the air, having only one carrier frequency of sound without a second signal, to a television receiver, since it is a superheterodyne with double frequency conversion. If, instead of fpchi, a signal with a frequency of 38 MHz from an additional generator is fed into the circuit, then we will be able to receive broadcasting stations with frequency modulation (FM-FM).
In other words, to solve this problem, it is necessary to manufacture an external local oscillator (a 38 MHz sinusoidal signal generator with high frequency stability) and apply a signal from it to the input of the UCHI. Tuning to the station is performed using a tuning potentiometer by changing the voltage on the varicaps SK-M-24-2S.
It should be noted that when the power supply of the additional generator is turned off, the broadcasting station will not be listened to.
principled circuit diagram additional generator is shown on fig.1. This is a classic capacitive three-point with a QZ1 quartz resonator at 38 MHz. The circuit in the collector circuit of the transistor VT1 is tuned strictly to the first harmonic of the frequency of this resonator using a tuning capacitor C3.
Structural data of the coils of the generator circuit:
frame from television receivers UNT-47-III with a diameter of 8 mm (cylindrical screen);
L1 - the loop coil contains 10 turns of PEV-1 wire with a diameter of 0.5 mm with a tap from the 3rd turn (counting from the upper end of the coil).
L2 - the communication coil contains 2 turns of PEV-1 wire with a diameter of 0.5 mm.
In the manufacture of the contour, first L2 is wound at the bottom of the frame, and then L1. A carbonyl iron core of the SCR-1 type is inserted into the end of the coil L1, which allows, if necessary, to change the inductance of the coil L1.
A drawing of the printed circuit board of the 38 MHz generator is shown in Fig. 2, and the location of the parts is in Fig. 3. PCB dimensions 67x43 mm.
The author made several stationary receivers from ZUSTST TVs, usually faulty. If space allows, for example, in a garage, then all the necessary alterations can be made without disassembling the TV completely, right in its case.
Since the receiver from the TV is used by the author only to listen to the soundtrack of TV programs and radio broadcasts, the power supply from the kinescope, the deflecting system, the TVS with a multiplier and the horizontal scanning transistor (KT838) are removed from the TV.
The VHF channel selector (SK-M-24-2S) has a control socket “Out. IF”, to which a prefabricated 38 MHz signal generator is connected through a 1.5 pF capacitor. Thus, the frequency from the additional generator will go to the submodule of the SMRK-2 radio channel, where it will be used to obtain a difference frequency of 6.5 MHz. When receiving sound from TV channels, the external generator power is turned off by an additionally installed switch.
Reception of broadcasting stations is made in the TV band |-|| (TV channels 1-5), which corresponds to an overlap in frequency of 49.75 ... .99.75 MHz, but in practice SK-M-24-2S receives signals with a carrier frequency of up to 107 MHz.
Although broadcasting generally uses vertically polarized waves, a conventional meter-wave television antenna generally provides normal reception. Nevertheless, for better reception of distant radio stations, it is better to use an antenna with vertical polarization or a conventional one. television antenna by rotating it 90°.
It should be noted that the sensitivity of such a receiver is quite high, and even a telescopic antenna can receive many broadcasting stations under favorable conditions.
If desired, the receiver can also be assembled in a case much smaller than the TV case. In this case, it is enough to remove only one module from the TV for use entirely - the radio channel module, for example, A1 MRK-2. On the board of this module, a UHF channel selector of the SK-D-24S type, an MB channel selector of the SK-M-24-2S type, a submodule of the radio channel SMRK-2, and a synchronization submodule of the USR are installed and interconnected. When receiving radio broadcasting and sound accompaniment of TV programs, the A1.4 (USR) board is not used, and it can be removed.
In order to simplify the receiver circuit, frequency tuning is carried out using a potentiometer connected to a rectifier with a voltage of 32 V. The potentiometer must have linear characteristic dependence of resistance on the angle of rotation of the movable contact (group A).
The 38 MHz additional signal generator is the same as described above. It is connected to the SK-M-24-2S to the “Out. IF" through a 1.5 pF capacitor. From the output of the SMRK, the audio signal is fed to the audio frequency power amplifier (UMZCH). UMZCH can be used with any sensitivity of the order of 70 mV. You can also use UMZCH on the K174UN7 chip from the same TV, which is located on the A9 board (BU-2-2 control unit). The supply voltage + 12 V is supplied to the UMZCH. The pin numbers of the connectors of the A1 board for connecting power, switching on the ranges, supplying the tuning voltage and the low-frequency signal output are shown in the block diagram of Fig. 4.
Using the SA1 switch, select the desired range, and when receiving broadcasting stations, you must turn on the SA2 switch ("PB") and apply power to the 38 MHz generator, and when receiving the sound of TV broadcasts, the SA2 switch must be turned off (the "TV" position),
The receiver, assembled from blocks from the TV and two additional circuits, is powered by a stable voltage of +12 V and +32 V (to change the capacitance of the varicaps) from the power supply, the circuit of which is shown in Fig. 5.
This power supply uses a power transformer T1 type TS40-2, the half-windings of the secondary windings T1 must be turned on according to the diagram in Fig. 5.
In principle, in this PSU, you can use any power transformer with a power of 20 ... 30 W with suitable voltages for secondary windings 12.5...14V and 18...20V.
The power supply circuit has no features. To power the UMZCH and the radio channel, a bridge rectifier on VD3-VD6 diodes was used, and to control the varicaps, a circuit with voltage doubling on diodes VD1, VD2. The supply voltages are stabilized by the simplest stabilizers. To compensate for the voltage drop across the transistor VT2, a VD11 diode is introduced into the circuit.
Literature
1. Kuzinets L.M., Sokolov V.S. Nodes of television receivers. Directory. - M.: Radio and communication, 1987.
2. Schematic diagram of the TV Photon 381D.
S.Babyn. town Kelmenci, Chernihiv region
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Dual-band VHF FM radio receiver The basis of the device is a specialized microcircuit of the VHF FM radio receiver K174XA34A, it is equipped with an LED tuning indicator and UHF on the TDA2003 microcircuit.
Main specifications dual-band VHF FM radio receiver:
Operating frequency ranges,
MHz…………………65.8…74 and 87.5…108
Supply voltage, V……7.5…15
Sensitivity, µV……………..5
Minimum current consumption, mA………………50
Output power at a supply voltage of 9 V at a load with a resistance of 4 ohms, W……… 1.5
The signal received by the antenna, through pin 3 of the XT2 block, is fed to the input circuit L1C3C4 and then to the input of the RF receiver DA1. Tune to a radio station by changing the resonant frequency oscillatory circuit a local oscillator consisting of an inductor L2, a capacitor SU and a varicap VD1. A constant voltage is supplied from the variable resistor R7 to the varicap VD1, changing its capacitance, and hence the frequency of the local oscillator of the receiver DA1. The applied KV132A varicap provides coverage of two VHF FM broadcasting bands - 65.8 ... 74 and 87.5 ... 108 MHz and allows you to receive audio from television channels located between these bands.
On the transistor VT1 and the LED HL1, an indicator for tuning to a radio station is assembled. At pin 9 of the DA1 chip, constant pressure, inversely proportional to the level of the received signal. With fine tuning to the radio station, the voltage at pin 9 of DD1 decreases, the transistor VT1 opens and the HL1 LED turns on. The sensitivity of the indicator is set by selecting the resistor R5. The output signal 34 through the capacitor C16 is fed to the input of the pre-amplifier on the transistor VT2, and after amplification - to the volume control R13. Power amplifier 34 is assembled on a DA3 chip without the use of a heat sink, and its output power should not be more than 1.5 W. To obtain more power, the specified microcircuit should be installed on a heat sink. The receiver chip DA1 is powered by an integrated voltage regulator DA2.
All elements, except for variable resistors, are mounted on a printed circuit board made of one-sided foil fiberglass, the drawing of which is shown in fig.
Fixed resistors - MLT, S2-23, variable resistor R7 - SPZ-23A, SPO, SP4-1 with a resistance of 100 ... 220 kOhm, R13 - SPO, SP4-1 or SPZ-4V with a power switch. Oxide capacitors - K50-35 or imported, the rest - K10-17.
The K174XA34A chip can be replaced with its upgraded version of the KR174XA34R or the foreign analogue TDA7021, and the TDA2003 chip with the domestic K174UN14 chip. Analogues of the integral stabilizer KR142EN5A - 7805, VC7805CT
The KT361B transistor can be replaced with any of the KT203, KT209, KT361 series, and KT315B - with any of the KT312, KT315, KT342 series, the LED is red with a rated current of up to 20 mA. All coils are frameless, L2 is wound with PEV-2 0.8 wire, on a mandrel with a diameter of 6 mm and contains 7 turns, and L1 is wound with PEV-2 0.5 wire on a mandrel with a diameter of 5 mm and contains 5 turns. Dynamic head VA1 - any power up to 10 W and a voice coil resistance of 4 ... 8 ohms, for example 4GDSH-4. The receiver chip is installed in the panel. Terminal blocks - series 308 with a contact pitch of 2.54 mm.
When using a dual-band VHF FM radio receiver in adverse reception conditions (low ground, a great distance from the radio station), as well as to increase sensitivity, you can use a resonant radio frequency amplifier. Before setting up the receiver, an antenna is connected to pin 3 of the XT2 block - a piece of wire 1 ... 1.5 m long, and a dynamic head is connected to pins 1 and 2 and power is supplied. Tuning into radio stations, determine the tuning range. Comparing it with an exemplary radio receiver, the boundaries of this range are corrected by stretching or compressing the turns of the L2 coil. The range width can be changed by selecting the resistor R6, with a decrease in resistance, the range expands. By selecting the resistor R5, it is necessary to achieve a clear turn-on of the HL1 LED when fine-tuning to the radio station and turn it off when tuning. The maximum sensitivity is set by first tuning into a radio station near a frequency of 88 MHz. To do this, by reducing the length of the antenna, stretching or compressing the turns of the L1 coil, they achieve the best reception quality. At the end of the adjustment, the coils are fixed on the board with paraffin.
The idea to assemble a survey VHF receiver was born back in 1993, when television channel selectors with a frequency synthesizer appeared in the CIS. This opened up very interesting prospects, because the frequency stability of these selectors is very high and is determined only by the reference quartz resonator. But any television all-wave channel selector (SLE) also has such disadvantages as:
1. Large overlap ratio of resonant circuits in the range (only 3 sub-bands at 800 MHz). This spoils the selector and noise characteristics of the selector.
2. To branch the input signal over 3 subbands, it is necessary to make a complex system for matching the input circuits of the subbands. This inevitably leads to losses and, therefore, the SCR is slightly inferior in its noise parameters to the channel selectors of the meter or decimeter range, although the input amplifiers used in it, according to passport data, have a noise factor of 1.2 -1.4 dB.
A lot of other advantages of SLE compensate for these shortcomings and we decided to try it.
The first receiver on the Lithuanian "digital" selector KS-H-62 was designed to receive narrow-band FM stations of the 144 and 430 MHz amateur radio bands and was tested in 1994. The control program at that time was written by our friend A. Samusenko. The receiver had very good characteristics:
- continuous range from 50 to 850 MHz with a tuning step of 62.5 kHz;
- selectivity for the mirror channel - no worse than 70 dB;
- the bandwidth for the second 10.7 MHz IF was 15 kHz;
- sensitivity about 0.5 μV;
- frequency instability at room temperature is not worse than + - 1 kHz / hour at a frequency of 850 MHz;
The narrow-band FM detector was made on a K174XA6. The main selection for 10.7 MHz IF was determined by the FP2P-307-10.7M-15 quartz filter. In the future, with the advent of new interesting broadcasting stations on VHF, the receiver was finalized.
The new receiver is primarily intended for high-quality reception of broadcasting mono and stereo stations of the European standard and sound accompaniment of television stations in the MV and UHF bands. The receiver has a low-frequency block that allows you to receive stereo broadcasts with good enough quality. The receiver is designed so that it can be modified for specific conditions by connecting additional submodules to the RF unit. For example, to receive narrowband stations, you need to make a small submodule that can be easily connected to the main version. This will be useful for ultrashortwave radio amateurs and those involved in the repair of radiotelephones and radio stations. For large cities, it is desirable to improve the selectivity of the adjacent channel by making an additional IF filter submodule. To reduce the dimensions, this submodule is assembled on chip elements and soldered into the board instead of a single piezoceramic filter on the RF unit. The range of received frequencies can be extended up to 900 MHz using an imported channel selector designed for reception in the UHF range not up to 60, but up to 69 American standard channels. The program provides for such an option.
Main characteristics of the receiver:
Sensitivity (worst point) at 20 dB SNR - 2 µV (wide band);
Sensitivity (worst point) at 10 dB S/N ratio - 0.5 µV (narrow band);
The range of received frequencies is continuous from 50 to 850 MHz;
Selectivity on the mirror channel at frequencies from 50 to 400 MHz - 70 dB,
From 400 to 850 MHz - 60 dB;
Bandwidth for the first IF - 31.7 MHz for the level - 3 dB - 600 kHz;
The bandwidth for the second IF is 10.7 MHz in terms of level - 3 dB - 250 kHz;
The bandwidth for the second IF is 10.7 MHz in terms of level - 20 dB - 280 kHz;
Bandwidth for the third IF - 465 kHz in terms of level - 3 dB - 9 kHz;
Frequency tuning step - 50 kHz;
LF output power with a load resistance of 4 ohms - 2 x 15 W - nominal; 2 x 22 W - maximum;
The frequency range of the LF tract is from 20 Hz to 18 kHz with a frequency response unevenness of less than 3 dB.
ULF harmonic coefficient (at an output power of 15 W) - 0.5%;
The receiver supply voltage is 16 V (12 V is possible with a corresponding decrease in output power);
The receiver has:
- convenient digital indication of the tuning frequency and levels of volume, balance, treble and low frequencies, called channel number;
- 4 x 4 keyboard that allows direct dialing, recording and recall of 41 recorded channels, automatic search for stations up and down in frequency, step-by-step tuning (step - 50 kHz) up or down;
- silent reception mode;
- switching modes "narrow \ wide band";
- audio control - adjustments (volume, balance, bass timbre, treble timbre, switching to an external audio input, switching audio effects: Linear Stereo (linear stereo), Spatial Stereo (spatial stereo), Pseudo Srereo (pseudo-stereo) and Forced Mono ( forced mono), as well as when switching inputs, the audio processor can operate in Stereo, Stereo A and Stereo B modes.
- a non-volatile memory that stores the above audio adjustments for each channel;
- indication of the level of the input RF signal (S-meter);
- silent search and channel switching;
- remote control RC-5 remote control;
- quiet listening (MUTE mode), while listening to on-air programs through a separate amplifier for stereo phones and all audio adjustments are provided, and the ULF final stage is closed;
Receiver block diagram:
The receiver consists of four main blocks (Fig. 1):
1. On the RF block (A1) there is an all-wave channel selector (A1.1). The unit performs double frequency conversion, frequency detection and amplification of the received LF voltage or complex stereo signal (CSS). Also, a 5 \ 31 V voltage converter, a silent tuning circuit, AGC and an S-meter are made here. Submodules of narrowband reception (A1.3) and additional filter (A1.2) can be connected to the block.
2. The LF block (A2) performs stereo signal decoding, preamplification, bass and treble tone control, switching of stereo effects, bass power amplification and allows you to listen to programs through stereo phones, connect an external signal source to the receiver amplifier, connect speaker systems with an impedance of 4 to 8 ohms to the receiver power amplifier. The unit also contains three voltage regulators needed to power the rest of the receiver units.
3. The control unit (A3) incorporates a microcontroller that forms the I 2C control bus, an 8-digit dynamic indication, and a 4x4 keyboard. The current settings are stored in non-volatile EEPROM separately for each memory location. All major adjustments can be made from the remote control with RC 5 protocol.
4. The power supply generates a voltage of 16 V, which is necessary to power the entire receiver. The maximum load current is up to 4.5 A.
Consider the electrical circuit diagram of the receiver:
RF block (A1):
The receiver (Fig. 2) is built according to the superheterodyne circuit with double (with narrow-band reception, with triple) frequency conversion. The first conversion is carried out by a small-sized 5 V channel selector A1.1 - 5002 PH 5 (Temic) or KS-H-132 (Selteka) or SK-V-362 D (Vityaz), which incorporates a frequency synthesizer. The channel selector is controlled by the I2C bus formed by the control unit. The SAW filter of the 1st IF 1ZQ1 UFP3P7-5.48 is connected to the symmetrical output of the selector (pins 9.10) with a center frequency located in the range from 31.5 to 38 MHz (in our receiver it is 31.7 MHz) and a bandwidth in terms of level - 3 dB at about 800 kHz. Similar filters are used in televisions with a parallel sound channel and are available in small quantities from the authors. The filter output is matched by the 1L1 coil, which creates an oscillatory circuit with the filter output capacitance tuned to resonance at the operating frequency. This makes it possible to reduce the losses in the filter to 3-4 dB and narrow the bandwidth for the first IF to 500-600 kHz. Instead of a SAW filter, you can use a 3-circuit FSS - with coupling coils on the first and last circuits. In this case, the dimensions will only increase. The output impedance of the selector is purely active and is equal to 100 ohms. You can try to use here the usual 38 MHz SAW filter with a “two-hump” frequency response, used in radio channels modern TVs, but due to the fact that the bandwidth for the 1st IF in this case will be about 7 MHz, noise will probably increase and selectivity in the adjacent channel will drop (not tested).
After the 1st IF filter, a frequency converter on 1DA1 K174PS1 follows, at the output of which there is a 2nd IF filter - 10.7 MHz, made on one piezoceramic filter 1 ZQ 2 and matched by the contour 1L3,1L4,1C9. The local oscillator of the 1DA 1 microcircuit is stabilized by a quartz resonator 1B Q1 - 21 MHz, the coil 1L 2 (3.9 μH) is used to fine-tune the frequency of the quartz resonator. The filtered signal of the second IF is fed to 1DA 2 K174XA6, in which further amplification, limitation and detection of FM signals take place. The circuit 1L 7, 1C 21 is the circuit of the quadrature FM detector. In parallel, the IF signal is fed to the AGC, BSHN, S-meter circuit, assembled on transistors 1VT2 - 1VT6. Similar internal circuits K174XA6 are not used in this case. due to the high level of the input signal coming to its input, they work inefficiently. The transistor circuit has a large dynamic range and performs better. The filtered IF signal is amplified by a 1VT 2 resonant stage tuned to 10.7 MHz, then fed to a logarithmic detector made on a 1VT 4 transistor and a 1VD 4 diode. At low signal levels, the input impedance of the cascade is high due to the high resistance of the closed diode 1VD 4 in the 1VT 4 emitter circuit. The cascade works as a linear detector. With an increase in the signal level, the 1VD 4 diode begins to open, the input resistance of the cascade drops and shunts the input signal. From this point on, the cascade begins to work as a logarithmic detector. The detector characteristic can be changed by the base bias of the 1VT 4 transistor and the selection of the 1VD 4 diode. The rectified voltage is integrated on 1C 38 and the resistance 1R 20 + the input resistance of the emitter follower on 1VT 5 . The voltage, inversely proportional to the input signal, from the output of the 1VT 5 emitter follower through the dividers to 1R 25 and 1R 28 is supplied, respectively, to pin 1 of the channel selector (AGC) and to the key stages on transistors 1VT 6 and 1VT 3, in which the control voltage is double inverted and approaching it to the TTL signal, which is used to control the squelch and stop autoscanning. The complex stereo signal from pin 7 K174XA6 is fed to the operational amplifier 1DA4 KR544UD2. The amplifier amplifies the CSS by almost 3 times to the level of 300-600 mV, which is necessary for the normal operation of the stereo decoder
On the printed circuit board of the RF unit (A1), from the side of printing on the CHIP elements, a 5V \ 31V converter is assembled on a 1VT1 transistor. The converter is a self-oscillator with an operating frequency of about 400 kHz. This scheme is characterized by simplicity, the absence of home-made winding products (used in the coil circuit 1 L 5, 1L 6 - 1000 μH, are purchased products manufactured by many companies and available for sale in the Chip and Dip store in Moscow) and a low level of radiation. The main task of this converter is to get a voltage of 1-2 V more than the frequency synthesizer requires at a given tuning point. Therefore, at a frequency of 850 MHz, the voltage at the selector input will be about 33 V, and at a frequency of 50 MHz it may be 5-7 V due to the increased load. This must be taken into account when setting up the converter. It is best to check it without a selector at idle. The open circuit voltage should be 35-40 V. If there is no desire to assemble this circuit, then a separate winding on a transformer with a rectifier and a stabilizer on the KS531V is perfect.
On the circuit diagram of the RF block (A1) there is a chip 1 DD 1 PCF 8583 is a clock controlled by the I 2C bus, but, unfortunately, the clock is not yet used in this version of the program. There is a place for 1DD 1 on the printed circuit board. In the future, we plan to use it and this will not require any modifications to the circuit.
Details and possible replacements:
1. Channel selector A1.1
The selectors may differ from each other in the I2C bus exchange protocol, depending on the type of frequency synthesizer chip used. This receiver can use selectors with microcircuits of the series TSA 552x (Philips), allowing you to select the division ratio of the reference divider. We are interested in a step of 50 kHz or Ko = 640. Without changing this program, the following channel selectors allow you to do this: 5002PH 5 (Temic), KS-H-132 (Selteka), SK-V-362 D (Vityaz). They use the TSA 5522 frequency synthesizer. There are many others (for example, almost all Temic, Philips f.f. selectors with TSA 5520 and TSA 5526 microcircuits), but for them you will have to adjust the control program for a different I 2C exchange protocol. You can generally abandon the 5-volt selector and use a 12-volt one. According to the exchange protocol on the I 2C bus, selectors such as: KS -H -92 OL (Selteca), SK-V-164 D (Vityaz) are suitable.
In this case, you will also have to abandon the AGC system, because with these selectors the AGC should be 9 volts. The pinout and dimensions of these selectors also differ from the 5 volt version. The sensitivity and selectivity of the receiver will not change.
2. Inductors:
1L1 - 25 turns of wire PEV2 - 0.25 on a frame Ф5mm with a tuning core made of carbonyl iron or an RF choke with an inductance of 2.2 μH (for filters used by the authors).
1L3, 1L4 - standard coil with built-in capacitor f. TOKO or similar with lilac or orange color marking. Such coils can be purchased at radio markets or soldered from any broken Chinese-made soap box.
You can wind it yourself - 24 turns and 4 turns, respectively, on a 4-section standard polystyrene frame with a screen used in TVs of the 4th, 5th generations. Coil 1L4 is located in one of the sections on top of 1L3.
1L7 - Standard coil with built-in capacitor f. TOKO or equivalent with green or pink color coding. You can wind it yourself - 24 turns on a 4-section standard polystyrene frame with a screen, like coils 1L3, 1L4.
1L5, 1L6 - high frequency chokes EC24-102K - 1000 uH + -10%.
1L2, 1L8 - high frequency chokes EC24-3 R 9K - 3.9 μH + -10%. 1L 2 can be used the same as 1L 1.
3. Resonators and filters:
Resonator 1BQ1 - 21 MHz, 1BQ2 - 32768 Hz. 1ZQ1- described above.
1ZQ2 - small-sized piezoceramic filter at 10.7 MHz - (for example L10.7MA5 f. TOKO).
4. Semiconductors:
1VT1 - KT315 with any letter, 1VT3, 1VT4, 1VT6 - KT3102 with any letter. 1VT2 - KP303B,G,E, KP307B,G. 1VT5-KT3107 with any letter. All diodes - KD521, KD522 with any letters.
5. Resistors: Permanent - C1-4 0.125 or MLT - 0.125, tuning - SP3-38B.
6. Capacitors: K10-17B - M47, K50-53 - 6.3V; 10V.
7. Connectors: XS 1, XS 2- OWF-8.
Additional filter submodule (A1.2) :
If in your area you can receive more than 7-10 stations in the "upper" broadcasting range, then to increase the selectivity in the adjacent channel, the printed circuit board provides for the installation of a more complex IF filter on two piezoceramic filters (Fig. 3). The total attenuation in this filter is 6-8 dB and is determined by an aperiodic compensating amplifier made on DA 1 S 595 (f.Temic). The gain of the cascade should compensate for the losses in the second filter ZQ 2 and it can be selected with a resistor R 1. It does not make sense to increase the gain and compensate for the losses of the two filters, because after the channel selector, which has a gain of at least 40 dB and K174PS1 - 20 dB, the signal level of the second IF is units and tens of millivolts. The filter with a compensating amplifier is made on chip elements and assembled on a separate board, which is soldered vertically instead of a single filter (points 1,2,3). The +5V power supply is brought to this board by a hinged mounting conductor, with a jumper located nearby on the RF unit (point 4).
About details:
Semiconductors:
Amplifier DA 1 S 595T (Temic) can be replaced by S 593T, S 594T, S 886T, BF 1105 (Philips) (this amplifier is a microcircuit consisting of a double-gate field-effect transistor with internal bias circuits along the first gate and source. Widely used in input circuits modern channel selectors).
Filters:
ZQ1, ZQ 2 - small-sized piezoceramic filters at 10.7 MHz - (for example L10.7MA5 f.TOKO).
L1 - RF choke EC24-3 R 9K - inductance 3.9 μH. It is possible to use any CHIP or MY coil (for example, manufactured by the Monolit software, Vitebsk with an inductance from 2.2 to 4.7 μH) to reduce the dimensions of the submodule.
Narrowband reception submodule (A1.3) :
The radio receiver allows you to receive stations with narrow-band FM. To do this, you need to make a narrowband reception submodule. circuit diagram submodule is shown in Figure 4. Narrowband receiver on a chip MC 3361 has no features and is assembled according to a typical scheme, repeatedly described in the literature. It allows you to receive high-quality radio stations with a frequency deviation from 1 to 5 kHz. This block is made on a separate printed circuit board and may not be manufactured. Switching SHP \ UP is carried out by the processor of the control unit, by pressing the button 3S 1 or from the remote control. This turns on the LED 3VD 1, logical “0” with P 3.6 (point 9) of the processor opens the transistor VT 1 of the submodule, which controls the relay K 1 of the submodule. The input of the operational amplifier 1DA 4 through the freely open contacts of the relay K 1 receives a low-frequency signal from MC 3361, where it is also amplified (the 10.7 MHz input is always connected and not switched). When connecting this unit, you need to remove the jumper J 1 on the RF unit. On the printed circuit board, this jumper is made in the form of a gap on the printed conductor between the 7th output of 1DA 2 and 1C 36 and is easily installed or not installed with a drop of solder during soldering. If possible, use a short, coaxial cable to connect the 9th point of the RF unit with the 8th point of the submodule. Further passage of the low-frequency signal through the stereo decoder does not affect the signal quality in any way.
Narrowband stations can also be received on the main version of the receiver without making a special submodule. To do this, increase to 10 kΩ resistor 1 R 8 (not forgetting to reduce it when receiving broadcasting stations) on block (A1). This resistor allows you to change the slope of the discriminator, so you can get a higher level of low-frequency signal from a small deviation. At the same time, you need to put up with the poor performance of the squelch due to the low levels of the RF signal of narrow-band stations and, nevertheless, the low level of the low-frequency signal. Resistor R 6 sets the squelch threshold.
If the frequency tuning step of 50 kHz is insufficient, then a smooth tuning of + -25 kHz can be introduced in the submodule by removing the quartz resonator BQ 1 at 10.235 MHz, capacitor C 4 and applying a signal to the 1st output of the DA 1 chip from a separate smooth generator with a level of 100-200 mV and a frequency from 10210 kHz to 10260 kHz.
About details:
Semiconductors:
DA1- MC3361 it can be replaced by KA3361, with a change in the circuit and printed circuit board - on K174XA26, MC3359, MC3371, MC3362.
Transistor VT1- KT3107, KT209.
Resonators and filters:
ZQ1 is a piezoceramic filter at 465 kHz. Any domestic or imported from radio receivers is suitable here.
BQ1 - quartz resonator 10.235 MHz.
L1 - standard coil with built-in capacitor C12 f. TOKO or equivalent for 465 kHz with yellow marking.
LF block (A2):
With 8 pin connector XP2 KCC goes to the stereo decoder circuit made on chip 2 DA1 LA3375 woofer block (Fig. 5).
Initially, the circuit used a cheaper TA7343P stereo decoder, but it did not stand up to criticism - the cascades following it were overloaded with a powerful subcarrier - 19 kHz, which appeared only on stereo stations and on the oscilloscope was 3 (!) Times more useful signal. Only LA3375 completely solved this problem. The LA3375 switching circuit is typical. The output of this microcircuit can additionally be used as a line output of the receiver.
Further, the low-frequency stereo signal is fed to the 2DA2 TDA8425 (Philips) audio processor, where amplification, frequency correction and all adjustments take place. sound signal. Then the low-frequency signal is fed in parallel to the 2DA6 TDA1552Q power amplifier and to the 2DA5 TDA7050 stereo telephone amplifier. The 5V power supply of this microcircuit (maximum 6 V, not 16 V as indicated in some reference books) is stabilized by a separate small-sized stabilizer KR1157EN5A (78 L05) 2DA5 . The TDA1552Q chip has a MUTE pin, which is controlled by the control unit processor through a 2VT1 transistor with a 2R17,2C43,2C45 delaying RC circuit and allows for absolutely silent channel switching. In the receiver, the MUTE mode is simultaneously turned on both in the terminal ULF and on the bus I2C for audio processor. Phones will hear a slight click when switching channels due to the fact that the MUTE mode of the audio processor is more inertial, as it is selected via the I2C bus. The unit has an additional linear low-frequency input (XS4) and can be used as a conventional power amplifier with convenient service. In this case, you can turn on the mode in which the signal from one input channel A or B goes to two channels of the amplifier at once.
Stabilizers 2 DA4, 2DA7 allow you to get rid of processor noise and dynamic indication as much as possible and serve to power the analog and digital parts of the circuit, respectively.
Details and possible replacements:
1. Semiconductors
2VT1 - KT3102 with any letter. Instead of bridge ULF 2 DA6 TDA1552Q, you can use similar -TDA1553Q, TDA1557Q by adding a 100 uF –16 V capacitor to pin 12. There is a place for it on the printed circuit board.
2DA3 - small-sized voltage regulator 78L05 or KR1157EN5A.
2. Resistors constants - C1-4 0.125 or MLT - 0.125, variables - SP3-38B.
3. Capacitors: K10-17B - M47, K50-53 -16 V. 2S32, 2S37-K50-53 - 25 V.
4. Connectors: XP2-OHU-8.
Control unit (A3) :
The control unit (Fig. 6) is made on an AT89C52-12 PC 3DD4 microcontroller with 8 kB internal ROM and generates control signals via the I2C bus to control the 1A1 channel selector (HF unit (A1)) and the TDA8425 2DA2 audio processor (LF unit (A2)) , non-volatile ROM 3DD1 (later also single-chip clock 1DD1PCF8583) . The control unit has a keyboard 4x4 3S3 - 3S 18 + 2 additional buttons 3S 1, 3S2, 9-digit led indicator 3HG1-3HG3 TOT3361AG (only 8 digits are used), LEDs 3VD6 - “STEREO”, 3 VD1 – “NARROW BAND”, photodetector 3DA1. Powerful repeaters KR1554LI9 3DD2, 3DD3 are used to increase the load capacity of the processor port P0. When the "quiet opening" is turned on, the dynamic indication is turned off, which serves as a source of interference. When the "NARROW STRIP" mode is enabled, LED 3 turns on VD1, the control signal from the same output of the microcontroller is fed to the narrowband reception submodule and the outputs of the low-frequency circuits K174XA6 and MC3361 are switched.
Signals coming from the control unit:
- serial two-wire bus I2C (SDA, SCL);
- MUTE signal - controls the output ULF TDA1552Q;
- switching signal UP\SHP
Signals incoming to the control unit:
- LED control “STEREO”;
- carrier identification signal;
- +5V digital;
The unit does not require any configuration and, if installed correctly, works immediately. You just need to memorize the current settings - more on that below.
A little about the details of the block:
1. Semiconductors:
3VT1-3VT8- KT3107, KT209.
3VD1, 3VD6 - AL307, 3 VD2-3VD5- KD521, KD522.
3DD2-3DD3 KR1554LI9, IN74AC34N.
3DD1- 24C04 (any non-volatile EEPROM with a capacity of 1 kB, controlled by bus I2C).
3DA1 SFH-506 - integrated photodetector. Can applyany from TVs of 5-6 generations or imported, such as ILMS5360.
3DD4 - AT89C52-12PC or any of this family with 8 kB of memory.
2. Buttons : 3S1-S18 - PKN-159 or TS-A1PS-130.
3. Resonator – 10 to 12 MHz of any type.
4. Resistors - C1-4 0.125 or MLT - 0.125, SP3-38B.
5. Capacitors: K10-17B - M47, K50-53 - 6.3 V.
6 . Connectors: XP1-OHU-8.
Power supply (A4) :
Received power supply parameters:
Load current - 4A
Voltage - 16V
Voltage instability at a pulse current load of 4A - no more than 0.1 V.
Emission of interference, even in close proximity to the receiver and without shielding, was not detected either at low frequency or at the operating frequencies of the receiver. The interference spectrum is concentrated in the region of 8-9 MHz with a level of about 500 μV at a distance of 0.5 cm from the pulse transformer.
It was decided to make this power supply according to a single-cycle scheme and squeeze out the maximum power and minimum interference radiation from it. Schematic diagram of the power supply is shown in Fig.7. Management is performed on a very common and cheap microcircuit 4DA2 UC3844 or UC3842. key element is a MOSFET 4VT1 (BUZ 90, KP707G, IRFBC40). Current feedback is removed from the source 4VT1. The output voltage is controlled by a parallel-type stabilizer 4DA2 TL431 (KR 142EN19). Feedback by voltage with p The decoupling of the primary and secondary circuits is carried out through an optocoupler 4DA1 AOT128A (4N35). The rectifier of the secondary circuit is made on a double Schottky diode 4VD8, 4VD9 KDS638A. The 4T1 power filter transformer is made on a ferrite ring magnetic core K20x12x6 M3000NMS. Transformer 4 T2 is made on an imported magnetic circuit with a frame f. Epcos and consists of 3 parts (described in the Radio magazine N 11 2001 and sold in the Chip and Dip store in Moscow):
1. B66358-G-X167 Ferrite N67 ETD29EPCS (2 halves with 0.5mm gap);
2. B66359-A2000 , transformer brace ETD29EPCS ;
3. B66359-B1013-T1 , transformer frame ETD29EPCS ;
Transformer winding data :
4T2- winding 7 - 13it is wound in 2 layers of 34 turns, evenly laid along the entire length of the frame with a PEV 2-0.4 wire. Winding 9 - 12 and 4 -5 are laid between winding layers 7-13. Winding 9-12 contains 9 turns of PEV 2-0.4 wire, laid evenly along the entire length of the frame. Winding 4-5 is wound in two wires and contains 10 turns of PEV 2-0.63 wire laid evenly along the entire length of the frame.
Structurally, the power supply consists of two printed circuit boards– control and power boards. On the diagram, the points of their connection are indicated by respectively numbered points. For example 1-1^ . To reduce the size, both boards are placed on racks one above the other. Feedback voltage from the output of the power supply to the control circuit 4R19-4R21, 4DA2 is supplied with a short shielded wire. The power supply has no other features and, with proper assembly, starts working immediately.
RECEIVER SETUP
- RF generator G4-176;
- Oscilloscope S1-99 (S1-120);
- Frequency response meter X1-48;
- LF generator G3-112;
- HP ESA-L1500A - spectrum analyzer.
RF block(A1) :
Without soldering the outputs of the channel selector to the board, you need to connect one of the filter inputs to a common wire, and apply an FM signal with a frequency of 31.7 MHz with an amplitude of 50 mV and a deviation of 50 kHz to the second one. Apply power 8-9 Volts to the input of the stabilizer 1DA3. Oscilloscope to control output 18 1 DA2. With tuning cores of coils 1 L1 and 1 L3, it is necessary to achieve the maximum amplitude of the signal at the input of the K174XA6 microcircuit. Depending on the filter used 1st IF, 1L1 can be replaced by a constant RF coil from 1.5 to 3.9 μH (maximum resonance), the same type as 1L2, 1L5, 1L6, 1L8. An additional sign of inaccurate contour tuning can be the appearance of AM modulation of the RF signal, which is clearly visible on the oscilloscope at a slower sweep time. The oscilloscope probe must be connected to the connection point of the 1C33 capacitor with the 1R13 resistor and achieve a maximum swing of 10.7 MHz at this point by adjusting the 1C31 capacitor.
Using an oscilloscope, check the output of the KSS on the contact 8 connectors XS2 . The LF signal must have a correct sinusoidal shape. To achieve an undistorted form of the low-frequency signal, you need to adjust the coil discriminator 1 L7, while an oscilloscope with a closed input needs to control pin 7 of microcircuit 1 DA2.
Check the collector of the transistor with an oscilloscope 1 VT1 converter 5V / 31V. If the cascade is operational, then the collector should have a sinusoid with a frequency of about 400 kHz and a span of 15-20 V. If there is no generation, then there is an 80% chance that you have a break in one of the coils 1 L5, 1 L6 or one of the chip capacitors is broken . 20% chance that one of the capacitors is out of specification.
After that, you can connect the channel selector and apply an input signal with an amplitude of 50 mV, a frequency of 100 MHz to its RF input. Frequency deviation 50 kHz.
Using a high-resistance voltmeter or oscilloscope, check the selector pin 1 (AGC voltage). Trimmer resistor 1 R25 set the voltage to 3.5-4V without an input signal and with an input signal of 50mV, the voltage should drop to 1.5-2V. the drain of transistor 1 VT2, trimming the trimmer 1C31 or replacing transistor 1 VT2 with a transistor with a greater slope S. In rare cases, the selection of a resistor 1R15 is required.
Reduce the voltage of the RF generator to 10 - 15 µV. Trimmer resistor 1 R2 8 it is necessary to achieve a clear operation of the BSHN system when the RF signal is turned on and off. The same trimming resistor automatically sets the threshold for stopping the scan. Scanning stops when a carrier appears, typically 2-3 steps from the broadcaster's center frequency. In this regard, fine tuning to broadcasting stations is done manually.
With a 1R21 trimmer, you can calibrate the S-meter in units that are convenient for you. For example, according to the 9-point S - scale adopted by radio amateurs on short waves (since this receiver close in sensitivity to HF, and not to VHF equipment). Then the maximum signal level can be taken as 9 + 60 dB, which corresponds to a voltage at the selector input of 50 mV (if a collective TV antenna is used, then such levels are quite possible). 9 points + 40 dB - 5 mV, 9 + 20 dB - 500 μV, 9 points - 50 μV, 8 points - 25 μV and so on through 6 dB. Less than 5 points should not be calibrated. this is already at the threshold of sensitivity of the AGC system. You can see the end-to-end frequency response of the receiver by applying a signal from the MFC of the frequency response meter X1-48 at a frequency of 100 MHz to the selector input. Set the meter marks to 1+ 0.1 MHz. Detector RF head control 18 output 1 DA2. The frequency response should have a regular bell-shaped shape without kinks and protrusions (it can be double-humped with a dip of no more than 2-3 dB) centered at a frequency of 100 MHz. The frequency response should not change shape at input signal levels from -60 dB to -30 dB. The shape of the frequency response can be slightly adjusted with the tuning cores of the 1L1 and 1L3 coils. If it is not possible to achieve the required parameters, then you need to choose piezoceramic filters 4ZQ1, 4ZQ2 from the same batch. In case of installing a single piezo filter 1ZQ2 requirements for it are simplified.
Coil 1L2 allows you to accurately set the frequency to 21 MHz. The printed circuit board provides for the option of installing both a standard choke (3.9 μH) and a coil with a tuning core, made according to the same data as 1L1. This is necessary to accurately hit the channel if a narrowband block is used. To obtain an accurate VCO frequency, it is also desirable to accurately set the frequency of the 4 MHz reference oscillator of the channel selector frequency synthesizer.
The reference oscillator is best tuned in narrowband reception mode, at the highest operating frequency of the channel selector - 850 MHz. Tune the receiver to this frequency in narrowband reception mode. Perhaps the actual tuning frequency will differ by + - 30 - 40 kHz - find it by adjusting the generator. The signal level from the G4-176 generator is about 5 0 µV, frequency deviation 5 kHz. Carefully unsolder or remove the upper and lower selector covers. Find a quartz resonator. On the print side, find a chip - a capacitor connected in series with the resonator. It is necessary to select its capacitance in the range from 18 to 22 pF with 1-2 pF chip capacitors (most often soldering in parallel with the main one) and at the same time adjust the frequency of the RF generator until you achieve “hit in the channel”. With narrowband reception, it is well audible. If it is possible to use a spectrum analyzer, then everything is simplified. You need to "see" the VCO frequency and set it by selecting capacitors with an accuracy of + - 1 kHz. This work is best done with a soldering iron with a tip of about 2 mm in diameter. We achieve by this method a frequency mismatch of no more than + - 500 Hz at 850 MHz, which is quite enough. If you do not have experience with chip elements, then it is better not to do this work, but to accept the fact that the frequency on the indicator may differ slightly from the real one (at frequencies up to 200 MHz, no more than 2-3 kHz - depends on the RMS) . In this case, you can make a smooth 10.235 MHz oscillator, which compensates for the frequency mismatch and allows you to receive stations that do not fall into the 50 kHz step.
Additional filter submodule ( A1.2) :
It does not need to be configured. When installing in the receiver, you need to make sure that the submodule is working correctly. This can be done with an oscilloscope or frequency response meter. If the IF voltage of 10.7 MHz is approximately the same at the input and output of the submodule, then the circuit is working. The shape of the frequency response can be corrected by adjusting the circuit 1L3, 1L4, 1C9 on the RF unit.
Narrowband reception submodule ( A1.3) :
The submodule is configured prior to installation in the receiver. At the input (point 8), you need to apply an FM signal with a frequency of 465 kHz, a deviation of 3 kHz, an amplitude of 10 μV. All customization is contour tuning L1 until the maximum amplitude of the low-frequency signal at the output of the submodule (14 pin DA1) is reached. Then, as part of the receiver, you need to set the noise suppressor threshold with resistor R6. To do this, you need to apply a signal to the receiver input from a generator with a frequency of 145 MHz, an amplitude of 20 μV, a deviation of 3 kHz, turning the generator output voltage on and off. The noise suppressor should operate steadily when an input signal of about 0.5 - 1 μV is applied.
LF block(A2) :
In this block, only the stereo decoder needs to be configured.
In the absence of a stereo modulator, we tuned the stereo decoder according to the signal of the radio station.
Tune the receiver to a stereo station in the 88-108 MHz band. By turning the trimmer resistor 2 R12, turn on the 3VD 6 "STEREO" LED on the control board. Place the resistor in the middle of the capture zone. Install the oscilloscope probe on any of the outputs of the stereo phones of the LF block and, by rotating the trimmer resistor 2 R3, achieve the greatest subcarrier suppression of 19 kHz from the oscillogram. This can be done without an oscilloscope - by ear. A sharp disappearance of distortions will indicate correct setting. Select the highest quality stereo station on the range and, by rotating the trimmer 2 R1, achieve the maximum separation of the stereo channels, which subjectively looks like an increase in the depth of the stereo base. We recommend setting up the stereo decoder by ear, using stereo phones.
Control block (A3) :
Power Supply ( A4):
Does not need setting.
This completes the configuration of the entire receiver.
OPERATION WITH THE RECEIVER:
Keyboard:
consists of 18 buttons with conditional numbers from 0 to 18 .
Let's take a look at all the buttons.
1 - while dialing the frequency and channel number for recording - the number 1. In the operating mode - adjusting the "-" stereo balance ( bL) .
2 - while dialing the frequency and channel number for recording - the number 2. In the operating mode - adjusting the "+" stereo balance ( bL).
3 - while dialing the frequency and channel number for recording - the number 3. In the operating mode - adjusting the "-" volume ( VOL).
4 - while dialing the frequency and channel number for recording - the number 4. In the operating mode - adjusting the "+" volume ( VOL).
5 - while dialing the frequency and channel number for recording - the number 5. In the operating mode - adjusting the "-" treble tone ( Hi).
6 - while dialing the frequency and channel number for recording - the number 6. In the operating mode - adjusting the "+" treble tone ( Hi).
7 - while dialing the frequency and channel number for recording - the number 7. In the operating mode - adjusting the "-" bass tone ( LO).
8 - while dialing the frequency and channel number for recording - the number 8. In the operating mode - adjusting the "+" bass tone ( LO).
9 - while dialing the frequency and channel number for recording - the number 9. In the operating mode - switching line input \ receiver. You can switch mono signal from any channel to two channels (Stereo, Stereo A, Stereo B).
10 - while dialing the frequency and channel number for recording - the number 0. In the operating mode - selection of stereo effects (LIN STEREO - normal stereo, SPATIAL STEREO - theater effect, PS STEREO - pseudo stereo, FORCE MONO - mono for two channels.)
11 – button "H" - turns on the frequency dialing mode.
12 – button "P" - record in the memory of the current frequency and audio adjustments for each channel.
13 – tuning down by 50 kHz.
14 – tuning 50 kHz up.
15 – enumeration of the recorded memory cells - one back.
16 – enumeration of the recorded memory cells - one ahead.
17 – “UP\SHP” button – switches on the narrowband reception mode.
18 – “SCAN” button – turns on the scanning mode.
When the receiver is turned on, the message appearsSEC850.
Frequency set:
Press button 11, the display will show N - - - - -- pick up the frequency.
- if the frequency is less than 100 MHz, then you need to dial the first zero for example ( 071,50 ) - it is not indicated on the indicator - 71,50 ;
- if you made a mistake, then press button 11 again and dial again;
- before memorizing, set the adjustments to the desired position so that they are also memorized for each of the recorded channels.
Setting adjustments:
- using buttons 1 to 10 set the adjustment values on each channel, which will be called up when the receiver is turned on.
Memory entry:
- press the button 12 , the display will show: - - 71,50 instead of dashes, you need to enter a two-digit cell number (from 00 to 40, when dialing a channel number over 40, the channel number 40 is recorded by default) for example: 00 – this cell is called when enabled.
We get: 71,50 (leading zeros are not displayed).
- alternately calling up the frequency dialing and memorizing modes - write down all the frequencies of the radio stations that interest you (from 0 to 40) .
- you can remove the frequency from the memory by writing the number 0 to all digits in this cell, in this case, a complete software reinitialization of the receiver takes place.
Scan mode:
- press button 18 the display will show: -SCAN-;
- press button 13 or 14 depending on which direction you want to search - up or down in frequency;
- you can exit the scanning mode by pressing button 18 again;
Note - the scanning mode is optional, so it is performed according to the simplest algorithm - carrier search. To fine-tune to broadcast stations, use buttons 13 and 14.
Narrowband reception mode:
This mode is activated by pressing button 17 or the corresponding button« AV » PDU. This turns on the LED 3VD6 on the control unit. By pressing the button 17 again, the receiver returns to the broadband reception mode.
Working with remote control:
- the program is written for the remote control-7 buttons from the Vityaz TVs, but the main functions will work on any remote control with the RC-5 protocol;
- buttons "0 - 9" call the corresponding number of the recorded memory cell;
- “OK” button – selection of adjustments: volume, balance, tone;
- buttons "P +" and "P-" - scroll through the ring of memory cells up or down;
- red, green, orange and blue buttons - selection of stereo effects;
- "ESC" - reset, software reinitialization of the receiver;
- "PP" - setting all adjustments to the middle position;
- mute button - quiet listening through stereo phones;
- button "i" - switching inputs 1 \ 2;
- buttons "+" and "-" in the bottom row - frequency tuning up or down by 50 kHz;
- button "turn off the network" - turn on the quiet mode;
- button "fixation of teletext page" - enable autoscanning;
- “AV” button - turn on narrowband reception;
Structurally, the receiver is made on four main and two additional printed circuit boards in accordance with the breakdown into blocks according to the circuit diagram. The case was not specially developed, because. not everyone is satisfied with a switching power supply. For a linear power supply with a power of about 70 watts, a different package is needed. One of the options for the front panel of the receiver with dimensions is shown in Fig. 8.
The channel selector is soldered to the PCB at four corners. When mounting the receiver into the housing, great attention should be paid to the wiring of additional "grounds" between the blocks. The presence or absence of LF interference from dynamic indication will depend on this. It is desirable to make signal wires between blocks short and shielded. For high-quality reception of stereophonic broadcasting, you can use an antenna from a collective television system (if it has a main amplifier for one of the channels from 2 to 5).
The power supply can be applied to any design at 16 volts with a maximum current about 4 A.
On such a receiver with a dipole antenna on the roof of a 7-storey building in October 2000 in Vitebsk, not only Vitebsk stations but also “EUROPE +” - Smolensk (102 MHz), “ BA" - Minsk (104.6 MHz), "Radio Style" - Minsk(101.2 MHz).
Over the course of two years, the authors assembled and tuned more than 10 such receivers, and all of them had good repeatability. The playback quality of radio programs is high, especially in stereo phones. Having made this receiver, at the same time you can get rid of the power amplifier you have if its output power is less than 20 watts per channel.
Probably the receiver circuit could be optimized and improved, or even performed on a different element base. There is no limit to improvement. We wanted to show the non-standard use of "digital" channel selectors, which are undeservedly much less popular than conventional analog channel selectors.
We would like to express our deep gratitude to our friends and colleagues for their help - Sergey Chirkov, who developed the power supply specifically for the receiver, and Vladimir Timoshenko, who made all the receiver circuits in electronic form.
The whole receiver (without power supply) costs about $25 - $30. All equipment (including capacitors and connectors) was purchased by the authors at the Chip and Dip store and at the radio market in Mitino - Moscow. You can also buy a channel selector there. KS-H-132 for $3.5 - $4. Much to the receiver can be bought at the Minsk radio market.
The authors hope that this article will not leave you indifferent and will be glad for any of your feedback. and suggestions. Order "stitched" processors, filters, printed circuit boards and get answers to all questions by contacting the authors by e-mail. For those who want to do everything themselves, in this publication, in addition to the diagrams, printed circuit board drawings and a microcontroller “firmware” map are published.
pcb_mirror. zip (346kb)
The proposed VHF FM receiver is a functionally complete design with a linear output, connected to a low-frequency power amplifier. Designed to receive stereo broadcasting signals with a "pilot-tone" system in the range of 88...108 MHz. The receiver tuning step is 0.05 MHz. Supply voltage - 9 V. Consumption current - 90 mA. The real sensitivity is no worse than 3 μV.
Several ideas are implemented in the design of the receiver.
Firstly, the receiver has an easy setup that any housewife will understand. There are 6 buttons for channel selection and 2 buttons for adjusting the selected channel (increase and decrease frequency). There is also an alternative option using an encoder for those who prefer to "twist" the setting.
Secondly, the minimum and sufficient indication is used on an available four-digit seven-segment indicator with a common anode. Thirdly, despite the seeming complexity, this receiver is technically easy to assemble and configure, and also cheap in terms of the composition of electronic components.
The receiver consists of two units: a control unit and a tuner unit. Structurally, these blocks are assembled on two boards. The schematic diagram of the control unit is shown below.
The basis of the control unit is the Microchip PIC16F628A microcontroller. To increase the number of digital lines, an extension implemented on the 74HC595 latchable shift register, which is available from many manufacturers, is used.
For indication, a four-digit seven-segment LED indicator with a common anode of the LTC-5623 type from Liteon is used. Indicators similar in pinout are also produced by other companies, for example, the RL-F5620 indicator. If you do not find a suitable indicator, then its analogue can be assembled on any single-digit seven-segment indicators with a common anode by combining the segment lines of the same name (for this you will need to change the printed circuit board pattern).
The microcontroller sequentially writes bytes to the shift register: on the DS line it sets the next bit of the required logic level (0 or 1), then with the trailing edge of the signal (transition from 1 to 0) on the CH_CP line pushes this bit into the register and, finally, with the trailing edge on the line ST_CP causes the last eight bits written to the register outputs.
The so-called dynamic indication is implemented in hardware and software - a special way of working when segments in character images are lit alternately at certain time intervals. To indicate the fractional part of the tuning step of 0.05 MHz, a decimal point in the fourth digit is used, the inclusion of which is understood as this “tail”. In order to increase the load capacity of the microcontroller, keys on KT3107 transistors were used (with any letter index).
Buttons are connected to the segment lines. The polling of buttons occurs simultaneously with dynamic indication, which leads to an instant assessment of the states "pressed" or "released". To prevent the buttons from shunting the segments of the indicator, a resistor R6 is connected in series, as a result, the current flows through the circuit with less resistance.
The incremental encoder type PEC12 is used. It can be replaced with a suitable pinout encoder from the EC11 series. Also on sale you can find other names of encoders that are identical in pinout with PEC12.
The values of resistances and capacitors in the control unit may differ from those indicated within +/-20%. It is possible to use any normally open buttons of suitable dimensions, for example, tact buttons TS-A6PG-130. We will replace the microcircuit stabilizer 7805 with KR142EN5A.
The tuner contains a minimum of radio components and does not contain rare or expensive items. It is possible to carry the requirement of minimization of the sizes of conclusions of components and conductors to features of circuit engineering. The tuner unit is assembled on a TEA5711 single-chip receiver chip from Philips and a frequency synthesizer chip LM7001J from Sanyo. A schematic diagram of the tuner block is shown in fig. 2.
The TEA5711 chip is a single-chip superheterodyne stereo VHF radio receiver. The signal from the local oscillator of the TEA5711 receiver (pin 23) is fed through the isolation capacitor C23 to the input of the phase detector of the LM7001J frequency synthesizer (pin 11). LM7001J at the output of the frequency detector (pin 14) generates a signal that is fed to an inverting low-pass filter assembled on KT3102 transistors (with any letter index), and then fed to the control input of voltage-controlled generators. Chips TEA5711 and LM7001 is desirable to install on the panel to avoid overheating during installation.
Inductors are frameless without cores. Coil to coil is wound tightly: L1 - 7 turns on a 4mm mandrel, L2 - 10 turns on a 3mm mandrel, L3 - 12 turns on a 3mm mandrel. All coils are wound with PEL-0.5 wire.
LED HL1 of any type, for example, AL307. Polar capacitors are electrolytic, the rest are ceramic. Trimmer resistor R4 any small-sized, for example, type SP3-38A.
Ceramic RF filters ZQ1, ZQ2 and resonator ZQ3 at a frequency of 10.7 MHz. ZQ4 quartz in the circuit of the LM7001 exemplary oscillator - 4 MHz (programmatically converted to a more common quartz, since the original uses scarce quartz at 7.2 MHz).
Assembly, adjustment, order of work.
Printed circuit boards are made by any accessible way, for example, by the LUT method. Jumpers are soldered, low-profile components, then large-sized elements. The boards are washed with a suitable solvent and checked through the light for hairline short circuits and non-solders. We install the flashed microcontroller in the panel on the control board, carefully checking the correct position of the key.
We temporarily disconnect the control board from the tuner board. We supply power to the control board and watch the indicator's reaction to pressing the buttons and rotating the encoder. The settings in the channels, as well as the last selected channel, must be saved after repeated switching on.
We connect the control board and tuner. We connect headphones or an amplifier (for example, computer active speakers) to the output line of the stereo signal of the tuner. We connect a piece of wire 30-40 cm to the antenna input of the tuner. We supply power from a stabilized source. We tune in to the extreme station in the upper part of the range, pushing the turns of L2. Then we set the stereo reception mode with a tuning resistor R4. We find a position R4 at which all stations are received in stereo mode. In stereo mode, the HL1 LED is lit. On this setting can be considered complete.
Photographs and mounting drawings.
