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 check the holes in it, but so that SMD components solder everything from the top.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.Setting up a transistor receiver is, in principle, little different from setting up a tube receiver. After making sure that the low-frequency amplifier is corrected and the lamps or transistors of the receiver are operating in normal modes, proceed to adjusting the circuits. Tuning begins with the detector stage, then moves on to the IF amplifier, local oscillator and input circuits.
It is best to customize circuits using a generator high frequency. If it is not there, then you can tune by ear, using the received radio stations. In this case, you may only need an avometer of any type (TT-1, VK7-1) and another receiver, the intermediate frequency of which is equal to the intermediate frequency of the receiver being tuned, but sometimes they are tuned without any instruments. When setting up, the Avometer serves as an indicator of the output signal.
When setting up the IF amplifier circuits in a tube receiver, when an RF generator and a tube voltmeter are used for this purpose, the latter must not be connected to the lamp grid, since the input capacitance of the voltmeter is added to the capacitance of the grid circuit. When setting up circuits, a voltmeter should be connected to the anode of the next lamp. In this case, the circuit in the anode circuit of this lamp must be bypassed with a resistor with a resistance of about 500 - 1000 Ohms.
Having finished setting up the IF amplification path, proceed to setting up the local oscillator and RF amplifier. If the receiver has several bands, then the tuning begins with the KB band, and then proceeds to tuning.
Contours of the NE and LW ranges. Short-wave coils (and sometimes medium-wave), unlike long-wave coils, usually do not have cores; they are most often wound on cylindrical (and sometimes ribbed) frames. The inductance of such coils is changed when adjusting the circuits, moving or pushing apart the turns of the coils.
In order to determine whether the turns should be shifted or moved apart in a given circuit, it is necessary to alternately insert a piece of ferrite and a brass (or copper) rod into the coil or bring it closer to it. It is even more convenient to perform this operation if, instead of a separate piece of ferrite and a brass rod, you use a special combined indicator stick, at one end of which magnetite (ferrite) is fixed, and at the other - a brass rod.
The inductance of the RF amplifier circuit coil should be increased if, at the points where the circuits connect, the volume of the signal at the receiver output increases when ferrite is introduced into the coil and decreases when a brass rod is introduced, and vice versa, the inductance should be reduced if the volume increases when a brass rod is inserted and decreases with the introduction of ferrite. If the circuit is configured correctly, a weakening of the signal volume at the interface points occurs when both ferrite and brass rods are introduced.
The circuits of the NE and LW ranges are configured in the same order. Changing the inductance of the circuit coil at the coupling points is carried out in these ranges by appropriate adjustment of the ferrite core.
When making homemade contour coils, it is recommended to wind a few obviously extra turns. If, when setting up the circuits, it turns out that the inductance of the loop coil is insufficient, winding up the turns on the finished coil will be much more difficult than winding up the extra turns during the setup process itself.
To make it easier to adjust the contours and calibrate the scale, you can use the factory receiver. By comparing the angles of rotation of the axes of the variable capacitors of the tuned receiver and the factory one (if the blocks are the same) or the position of the scale indicators, determine in which direction the circuit adjustment needs to be shifted. If the station on the scale of the tuned receiver is closer to the beginning of the scale than that of the factory one, then the capacitance of the tuning capacitor of the local oscillator circuit should be reduced, and vice versa, if closer to the middle of the scale, it should be increased.
Methods for checking a local oscillator in a tube receiver. You can check whether the local oscillator is working in a tube receiver different ways: Using a voltmeter, optical tuning indicator, etc.
When using a voltmeter, it is connected in parallel with the resistor in the anode circuit of the local oscillator. If the short circuit of the capacitor plates in the local oscillator circuit causes an increase in the voltmeter readings, then the local oscillator is working. The voltmeter must have a resistance of at least 1000 Ohm/V and be set to a measurement limit of 100 - 150 V.
Checking the operation of the local oscillator with an optical tuning indicator (6E5C lamp) is also simple. To do this, the control grid of the local oscillator lamp is connected with a short conductor to the grid of the 6E5C lamp through a resistor with a resistance of 0.5 - 2 MOhm. The dark sector of the tuning indicator should be completely closed during normal operation of the local oscillator. By changing the dark sector of the 6E5C lamp when rotating the receiver tuning knob, one can judge the change in the amplitude of the generator voltage in different parts of the range. If the amplitude unevenness is observed within significant limits, more uniform generation over the range can be achieved by selecting the number of turns of the coupling coil.
The operation of the local oscillator of the transistor receiver is checked by measuring the voltage at the local oscillator load (most often at the emitter of the transistor of the frequency converter or mixer). The local oscillator voltage, at which frequency conversion is most effective, lies in the range of 80 - 150 mV on all ranges. The voltage across the load is measured with a lamp voltmeter (VZ-2A, VZ-3, etc.). When the local oscillator circuit is closed, its oscillations are interrupted, which can be noted by measuring the voltage across its load.
Sometimes self-excitation can be eliminated very in simple ways. So, in order to eliminate self-excitation in the IF amplification stage, a resistor with a resistance of 100 - 150 Ohms can be connected to the control grid circuit of the lamp of this stage. The amplification of the intermediate frequency voltage in the cascade will decrease slightly, since only a small part of the input signal voltage is lost across the resistance.
In transistor receivers, self-excitation can occur if the battery or batteries are discharged. In this case, the battery should be replaced and the batteries should be charged.
In some cases, self-excitation in the receiver and TV can be eliminated by such measures as moving the grounding individual elements circuits, alteration of installation, etc. The effectiveness of measures taken to combat self-excitation can often be assessed in the following way.
Rice. 25. To explain the method of eliminating self-excitation in transistor reflex receivers
The receiver or TV is connected to an regulated power source (that is, to a source whose voltage supplied to the anode circuits can be varied within wide limits), and a lamp voltmeter or other dial indicator is turned on at the output of the receiver. Since at the moment self-excitation occurs, the voltage at the output of the receiver changes sharply, the deviation of the indicator arrow makes it easy to note this. The voltage taken from the source is controlled by a voltmeter.
If self-excitation occurs at the rated voltage, then the supply voltage is reduced to a value at which generation stops. Then they take certain measures against self-excitation and increase the voltage until generation occurs, noting it on a voltmeter. If the measures are successfully taken, the threshold for self-excitation should increase significantly.
In transistor reflex receivers, self-excitation can occur due to poor placement of the high-frequency transformer (or inductor) relative to the magnetic antenna. Such self-excitation can be eliminated by using a short-circuited turn of copper wire with a diameter of 0.6 - 1.0 mm (Fig. 25). A U-shaped wire bracket is threaded through the hole in the board, bent from the bottom, twisted and soldered to the common wire of the receiver. The bracket can serve as an element for fastening the transformer. If the transformer winding is wound uniformly on the ferrite ring, then the corresponding orientation of the short-circuited turn relative to other ferrite parts is not required.
Why does the receiver “howl” on the KB band. It can often be observed that a superheterodyne receiver, when receiving a broadcast station on short waves, begins to “howl” with a slight detuning. However, if the receiver is tuned more accurately to the station being received, reception becomes normal again.
The reason for the "howl" when the receiver operates on short waves is the acoustic coupling between the receiver's loudspeaker and the tuning capacitor bank.
This generation can be eliminated by improving the depreciation of the tuning unit, as well as reducing various accessible ways acoustic feedback- changing the method of mounting the loudspeaker, etc.
Setting up an IF amplifier using another receiver. At the beginning of this section, a method was described for tuning a radio receiver using simple instruments. In the absence of such devices, tuning radios is usually done by ear, without instruments. However, it should be said right away that this method does not provide sufficient adjustment accuracy and can only be used as a last resort.
To tune the IF amplifier circuits, instead of a standard signal generator, you can use another receiver, the intermediate frequency of which is equal to the intermediate frequency of the tuned receiver. -For a tuned tube receiver, the AGC wire running from the diode to the control grids of the adjustable lamps must be disconnected from the diode during setup and connected to the chassis. If this is not done, the AGC system will make it difficult to fine-tune the bandpass filters. In addition, when setting up an IF amplifier, it is necessary to disrupt the oscillations of the local oscillator by blocking its circuit with a capacitor with a capacity of 0.25 - 0.5 μF.
The auxiliary receiver used in this case does not need to be subjected to any significant modifications. To set up, you only need a few additional parts: a variable resistor (0.5 - 1 MOhm), two fixed capacitors and two or three fixed resistors.
Setting up amplifier circuits. The receiver IF is produced as follows. The auxiliary receiver is pre-tuned to one of the local stations operating in the long or medium wave range. Next, the common wires or chassis of both receivers are connected to each other, and the wire going in the tube receiver to the control grid of the lamp of the first IF amplification stage of the auxiliary receiver is disconnected and connected to the control grid of the lamp of the corresponding stage of the IF amplifier of the tuned receiver. In the case of setting up a transistor receiver, the IF signal through capacitors with a capacity of 500 - 1000 pF is supplied alternately to the bases of the transistors of the corresponding stages of the IF amplifier.
Then both receivers are turned on again, however, in order to avoid interference during tuning, the low-frequency part of the auxiliary receiver, as well as the local oscillator of the receiver being tuned, should be turned off (in tube receivers, by removing the lamps of the bass amplifier and local oscillator, respectively).
When setting up the IF amplifier stages of a transistor receiver, its local oscillator should be turned off by installing a jumper in the local oscillator circuit.
After this, by applying an intermediate frequency signal from the auxiliary receiver to the input of the IF amplifier being tuned and smoothly adjusting the settings of the IF circuits of the latter, we achieve audibility of the station to which the auxiliary receiver is tuned. Then they continue to adjust each circuit separately (to the maximum signal level), and the adjustment is best done using a pointer device connected to the output of the low-frequency amplifier, or using an optical indicator (6E5C lamp or similar).
Start tuning from the last inverter circuit; the signal is supplied to the base of the corresponding transistor or directly to the grid of the lamp in the anode circuit of which the tuned circuit is included.
If the setting is carried out not according to the optical indicator, but according to the sound volume, then it is recommended to set the volume level to minimum, since the human ear is more sensitive to changes in the volume level with weak sounds.
About tuning the receiver by radio stations. Tuning a superheterodyne receiver - tube or transistor - for received stations without using an auxiliary receiver usually begins on the KB band. By adjusting the IF circuits for maximum noise and rotating the tuning knob, the receiver is set to any of the audible stations. If it is possible to receive such a station, then they immediately begin to adjust the IF circuits, achieving maximum audibility (tuning begins with the last IF circuit). Then the heterodyne and input circuits are tuned, first at short, then at medium and long waves. It should be noted that setting up receivers using this method is complex, time-consuming and requires experience and skills.
Lamp 6E5S - indicator during setup. As already mentioned, it is not recommended to adjust the receiver circuits in terms of sound volume, especially if you are installing high level output volume. The sensitivity of the human ear to changes in signal level during loud sounds is very low. Therefore, if you still have to tune the receiver by sound, then the regulator should set low level volume, or, which is better, use an optical tuning indicator - a 6E5C lamp or another similar one.
By tuning superheterodyne receivers according to the received stations and using a 6E5C lamp as an indicator of tuning accuracy, it is more convenient to adjust the contours at an input signal level at which the dark sector of this lamp narrows to 1 - 2 mm.
To regulate the signal voltage at the receiver input, you can connect, for example, a variable resistance resistor in parallel with the antenna coil, the value of which, depending on the sensitivity of the receiver, can be selected in the range from 2 to 10 kOhm.
How to detect a faulty stage in an RF amplifier. When setting up or repairing a receiver, a cascade in which there is a malfunction can be detected using an antenna, alternately connecting it to the bases of transistors or to the grids of amplifier lamps and determining by ear by noise whether there are malfunctions in these cascades.
This method is convenient to use in cases where there are several RF amplification stages.
An antenna in the form of a piece of wire can also be used when testing the IF and RF amplification stages in televisions. Since shortwave stations often operate at frequencies close to the intermediate frequency of televisions, listening to these stations will indicate the serviceability of the audio channel,
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Every radio receiver has settings for a certain frequency, most of them even have fixed settings, which is very convenient. If the receiver is digital, that is, it has electronic tuning, then fixing one or another radio station on a specific channel will not be difficult. This process will be a little more difficult to occur on receivers with a regular tuning scale. But, in any case, the user manual describes in detail how to set up the radio and how many stations you can store in its memory. However, all this can be done only after purchasing this very radio. Many people are faced with the problem of choice these days, because there are so many different models in stores.
For those who want to listen to all radio stations, an all-wave receiver is the best option. And if it has the ability to receive VHF waves, then it will be simply happiness, because such receivers can also pick up radio conversations. Therefore, it is worth thinking about how to choose a radio receiver, for what purposes will it be used and what should it be like? If it is a “cabinet” receiver, then the standard FM and AM bands will be quite sufficient for it. For “portable” and “hiking” receivers, it is better to be able to “listen” to all frequencies, since hiking can also be in unfamiliar areas, where the radio can broadcast on any frequencies. With “portable” ones, you can just play around and eavesdrop on other people’s conversations if they use walkie-talkies.
If you can’t buy such a receiver, then you should think about how to assemble a radio receiver so that it can “hear” in the required range. To do this, you need to be a radio amateur, or have one of them as very close friends. You can, of course, scour the Internet and look for step by step instructions for assembling a radio receiver. But there are also pitfalls, because not all the necessary parts can be bought; some you have to make yourself. Therefore, if you have a friend who is a radio amateur, then you can ask him how the radio works, what parts you can buy, and which parts you need to make yourself and how, and most importantly, from what? After the answers to the questions have been received, you can begin to search for the necessary parts, both for the receiver and parts for the parts for your radio.
You will have to do a lot of shopping, look in the pantry for old equipment and rummage through it in search of the necessary parts. After this, you will have to spend a lot of time with a soldering iron in your hands and use up several grams of tin and wires. And now, when all the parts are ready, you will need to turn to a friend with the question of how to make a radio receiver so that it works reliably and for a long time. It doesn’t matter much what the radio receiver will be like. Both homemade and purchased receivers receive radio waves. If he brings pleasure to his owner, then he will fulfill his purpose.
Greetings! In this review I want to talk about a miniature receiver module operating in the VHF (FM) range at a frequency from 64 to 108 MHz. I came across a picture of this module on one of the specialized Internet resources, and I became curious to study it and test it.
I have a special awe for radios; I have loved collecting them since school. There were diagrams from the magazine “Radio”, and there were just construction kits. Every time I wanted to build a better and smaller receiver. The last thing I assembled was a design on the K174XA34 microcircuit. Then it seemed very “cool”, when in the mid-90s I first saw a working circuit in a radio store, I was impressed)) However, progress is moving forward, and today you can buy the hero of our review for “three kopecks”. Let's take a closer look at it.
View from above. 
View from below. 
For scale next to the coin. 
The module itself is built on the AR1310 chip. I couldn’t find an exact datasheet for it, apparently it was made in China and its exact functional structure is not known. On the Internet you can only find wiring diagrams. A Google search reveals: "This is a highly integrated, single-chip, stereo FM radio receiver. The AR1310 supports frequency range FM 64-108 MHz, the chip includes all the functions of FM radio: low noise amplifier, mixer, oscillator and low dropout stabilizer. Requires a minimum of external components. It has good quality audio signal and excellent reception quality. AR1310 does not require control microcontrollers and no additional software, except 5 buttons. Operating voltage 2.2 V to 3.6 V. consumption 15 mA, in sleep mode 16 uA ".
Description and specifications AR1310
- Reception of FM frequencies range 64 -108 MHz
- Low power consumption 15 mA, in sleep mode 16 uA
- Supports four tuning ranges
- Using inexpensive quartz resonator 32.768KHz.
- Built-in two-way function automatic search
- Support electronic volume control
- Supports stereo or mono mode (when contacts 4 and 5 are closed, stereo mode is disabled)
- Built-in 32 Ohm Class AB headphone amplifier
- Does not require control microcontrollers
- Operating voltage 2.2V to 3.6V
- In SOP16 housing
Pinout and dimensions module. 
AR1310 microcircuit pinout. 
Connection diagram taken from the Internet. 
So I made a diagram for connecting the module. 
As you can see, the principle couldn’t be simpler. You will need: 5 tact buttons, a headphone jack and two 100K resistors. Capacitor C1 can be set to 100 nF, or 10 μF, or not at all. Capacitances C2 and C3 from 10 to 470 µF. As an antenna - a piece of wire (I took a MGTF 10 cm long, since the transmitting tower is in my neighboring yard). Ideally, you can calculate the length of the wire, for example at 100 MHz, by taking a quarter wave or one eighth. For one eighth it will be 37 cm.
I would like to make a remark regarding the diagram. AR1310 can operate in different ranges (apparently for more quick search stations). This is selected by a combination of pins 14 and 15 of the microcircuit, connecting them to ground or power. In our case, both legs sit on VCC.
Let's start assembling. The first thing I encountered was the non-standard pin-to-pin pitch of the module. It is 2 mm, and it will not be possible to fit it into a standard breadboard. But it doesn’t matter, I took pieces of wire and just soldered them in the form of legs. 
Looks good)) Instead of a breadboard, I decided to use a piece of PCB, assembling a regular “fly board”. In the end, this is the board we got. The dimensions can be significantly reduced by using the same LUT and smaller components. But I didn’t find any other details, especially since this test stand, for break-in. 
After applying power, press the power button. The radio receiver worked immediately, without any debugging. I liked the fact that the search for stations works almost instantly (especially if there are many of them in the range). The transition from one station to another takes about 1 s. The volume level is very high, it is unpleasant to listen to at maximum. After turning off the button (sleep mode), it remembers the last station (if you do not completely turn off the power).
Sound quality testing (by ear) was carried out using Creative (32 Ohm) drop-type headphones and Philips vacuum-type headphones (17.5 Ohm). I liked the sound quality in both. There is no squeakiness, a sufficient amount of low frequencies. I'm not much of an audiophile, but I was pleasantly pleased with the sound of the amplifier of this microcircuit. In Philips I couldn’t turn up the maximum volume, the level sound pressure until it hurts.
I also measured the current consumption in sleep mode 16 μA and in working mode 16.9 mA (without connecting headphones). 
When connecting a load of 32 Ohms, the current was 65.2 mA, and with a load of 17.5 Ohms - 97.3 mA. 
In conclusion, I will say that this radio receiver module is quite suitable for domestic use. Even a schoolchild can assemble a ready-made radio. Among the “cons” (more likely not even cons, but features) I would like to note the non-standard pin spacing of the board and the lack of a display to display information.
I measured the current consumption (at a voltage of 3.3 V), as we see, the result is obvious. With a load of 32 Ohms - 17.6 mA, with 17.5 Ohms - 18.6 mA. This is a completely different matter!!! The current varied slightly depending on the volume level (within 2 - 3 mA). I corrected the diagram in the review. 
The high-frequency block contains a converter stage, input and heterodyne circuits. In receivers of the first and highest classes, as well as in the VHF range, there is a high-frequency amplifier in front of the converter. Checking and adjusting the high-frequency unit can be divided into three stages: 1) checking local oscillator generation; 2) determining the boundaries of the range, often called range laying; 3) pairing of input and heterodyne circuits.
Laying ranges. The tuning of the receiver to the received station is determined by the tuning of the local oscillator circuits. Input and UHF circuits only increase the sensitivity and selectivity of the receiver. When tuning it to different stations, the local oscillator frequency must always differ from the received frequency by an amount equal to the intermediate one. To ensure constant sensitivity and selectivity over the range, it is desirable that this condition be met at all frequencies in the range. However, this is the frequency ratio over the entire range
is ideal. With one-handed setup, it is difficult to obtain such a pairing. Local oscillator circuits used in broadcast receivers provide precise matching of the settings of the input and local oscillator circuits in each band at only three points. In this case, the deviation from ideal conjugation at other points of the range turns out to be quite acceptable (Fig. 82).
For good sensitivity on the KB range, two precise pairing points are sufficient. The necessary relationships between the frequencies of the input and heterodyne circuits are achieved by complicating the circuit of the latter. The heterodyne circuit, in addition to the usual tuning capacitor C 1 and tuning capacitor C2, includes an additional capacitor SZ, called a mating capacitor (Fig. 83). This capacitor (usually a fixed capacitance with a tolerance of ±5%) is connected in series with a variable capacitor. The inductance of the local oscillator coil is less than the inductance of the input circuit coil.
To correctly determine the boundaries of the range, you must remember the following. The local oscillator frequency at the beginning of each range is mainly affected by a change in the capacitance of the tuning capacitor C 2, and at the end of the range - by a change in the position of the inductor core L and the capacitance of the mating capacitor SZ. The beginning of the range can be considered the maximum frequency to which the receiver can be tuned in a given range.
When starting to set up the local oscillator circuits, you should find out the sequence of settings by range. In some receiver circuits, the CB band loop coils are part of the DV band loop coils. In this case, you need to start tuning with medium wave and then tune to long wave.
Most receivers use a band switching scheme that allows each band to be adjusted independently. Therefore, the configuration sequence can be any.
The range is set using the two-point method, the essence of which is to set the limit of the highest frequency (beginning of the range) using a tuning capacitor, and then the lower frequency (end of the range) with the core of the loop coil (Fig. 84). But when setting the limit of the end of the range, the setting of the beginning of the range is somewhat lost. Therefore, you need to check and adjust the beginning of the range again. This operation is performed until both points in the range are in compliance with the scale.
Pairing of input and heterodyne circuits. The setting is made at two points and checked at the third. The exact coupling frequencies in receivers with an intermediate frequency of 465 kHz for the middle of the range (f cf) and ends (f 1 and f 2) can be determined by the formulas:
The circuits are paired at design points, which for standard broadcasting ranges have the following values
In individual radio models, the pairing frequencies may vary slightly. The lower precision coupling frequency is usually selected 5...10% higher than the minimum frequency of the range, and the upper frequency is 2...5% lower than the maximum. Capacitors with variable capacitance allow you to tune the circuits to exact matching frequencies when turning at angles of 20...30, 65...70 and 135...140°, measured from the position of the minimum capacitance.
To configure tube radio receivers and achieve pairing, the output signal of the generator is connected to the input of the radio receiver (Antenna, Ground sockets) through the all-wave equivalent of the antenna (Fig. 85). Transistor radios that have an internal magnetic antenna are tuned!: using a standard field generator, which is loop antenna, connected to the generator through a non-inductive resistor with a resistance of 80 Ohms.
The decade divider at the end of the generator cable is not connected. The antenna frame is made square with a side of 380 mm from copper wire with a diameter of 4...5 mm. The radio receiver is located at a distance of 1 m from the antenna, and the axis of the ferrite rod should be perpendicular to the plane of the frame (Fig. 86). The magnitude of the field strength in μV/m at a distance of 1 m from the frame is equal to the product of the readings of the generator's smooth and step attenuators.
In the KB band there is no internal magnetic antenna, so the signal from the generator output is fed to the socket external antenna through a capacitor with a capacity of 20...30 pF or to a whip antenna through a decoupling capacitor with a capacity of 6.8...10 pF.
The receiver is tuned on a scale to the highest precise coupling frequency, and the signal generator is adjusted to the maximum voltage at the receiver output. By adjusting the tuning capacitor (trimmer) of the input circuit and gradually reducing the generator voltage, we achieve a maximum increase in the output voltage of the receiver. Thus, pairing is carried out at this point in the range.
Then the receiver and generator are tuned to a lower precise coupling frequency. By rotating the core of the input circuit coil, the maximum voltage is achieved at the output of the receiver. For greater accuracy, this operation is repeated until the maximum voltage at the receiver output is reached. After adjusting the contours at the edges of the range, check the accuracy of the pairing at the middle frequency of the range (third point). To reduce the number of tunings of the generator and receiver, the operations of setting the range and pairing the circuits are often performed simultaneously.
Setting up the LW band. The standard signal generator remains connected to the receiver circuit through the equivalent of an antenna. The generator is set to a lower frequency range of 160 kHz and an output voltage of 200...500 µV with a modulation depth of 30...50%. The lower coupling frequency is set on the receiver scale (the rotation angle of the KPI rotor is approximately 160...170°).
The gain control is moved to the maximum gain position, and the band control is moved to the narrow band position. Then, by rotating the core of the heterodyne circuit coils, the maximum voltage is achieved at the output of the receiver. Without changing the frequencies of the generator and receiver, the coils of the UHF circuits (if any) and input circuits are adjusted in the same way until the maximum voltage is obtained at the output of the receiver. At the same time, the generator output voltage is gradually reduced.
Having adjusted the end of the DV range, set the variable capacitor to the position corresponding to the coupling point at the highest frequency of the range (KPI rotation angle 20...30°). The generator frequency is set to 400 kHz, and the output voltage to 200...600 µV. By rotating the trimming capacitors of the circuits, first the local oscillator, and then the UHF and input circuits, the maximum output voltage of the receiver is achieved.
Tuning the circuits at the highest frequency of the range changes the tuning to lowest frequency. To increase the accuracy of the settings, the described process must be repeated in the same sequence 2...3 times. When re-adjusting the rotor, the KPI should be placed in the previous position, i.e. in the one in which the first adjustment was carried out. Then you need to check the accuracy of the pairing in the middle of the range. The frequency of the exact pairing in the middle of the LW range is 280 kHz. By setting this frequency on the generator and receiver scale respectively, the calibration accuracy and sensitivity of the receiver are checked. If there is a dip in the sensitivity of the receiver in the middle of the range, then it is necessary to change the capacitance of the coupling capacitor and repeat the tuning process.
The final stage is checking that the settings are correct. To do this, a test stick, which is an insulating rod (or tube), is inserted into the tuned circuit first with one end and then with the other end, with a ferrite rod fixed at one end and a copper rod at the other. If the adjustment is made correctly, then when any end of the test stick is brought to the circuit coil field, the signal at the receiver output should decrease. Otherwise, one end of the stick will reduce the signal, and the other will increase it. After the LW band is configured, you can similarly configure the MW and HF bands. However, as already noted, on the HF band it is enough to pair at two points: at the lower and upper frequencies of the range. In most radio receivers, the KB range is divided into several subbands. In this case, the exact pairing frequencies have the following values!
Features of setting the HF range. When tuning the HF band, the signal from the generator can be heard in two places on the tuning scale. One signal is the main one, and the second is the so-called mirror signal. This is explained by the fact that on the HF band the mirror signal is suppressed much worse, and therefore it can be confused with the Main signal. Let us explain this with an example. A voltage with a frequency of 12,100 kHz is applied to the receiver input, i.e., the beginning of the HF range. In order to obtain a frequency equal to the intermediate frequency at the output of the frequency converter, i.e. 465 kHz, it is necessary to adjust the local oscillator to a frequency equal to 12,565 kHz. When the local oscillator is tuned to a frequency of 465 kHz below the received signal, i.e. 11,635 kHz, an intermediate frequency voltage is also provided at the output of the converter. Thus, the intermediate frequency in the receiver will be obtained at two frequencies, the local oscillator, one of which is higher than the signal frequency by the amount of the intermediate frequency (correct), and the other lower (incorrect). In percentage terms, the difference between the correct and incorrect local oscillator frequencies is very small.
Therefore, when setting up the HF range, you should choose from two local oscillator settings the one that is obtained when smaller capacity circuit capacitor or with a more inverted coil core. The correct setting of the local oscillator is checked at a constant frequency of the generator signal. When increasing the capacitance (or inductance) of the local oscillator circuit, the signal should be heard in one more place on the receiver scale. You can also check the correctness of the local oscillator settings while keeping the receiver settings unchanged. When the frequency of the generator signal changes to a frequency equal to two intermediate ones, i.e., 930 kHz, the signal must also be heard. The higher frequency in this case is called the mirror frequency, and the lower frequency signal is the main one.
Setting up the antenna filter. Setting up the high frequency unit begins with setting up the antenna filter. To do this, the output signal of the generator is connected to the input of the receiver through the equivalent of an antenna. On the frequency scale of the generator, a frequency of 465 kHz and a modulation depth of 30...50% are set. The output voltage of the generator must be such that the output meter connected to monitor the output voltage of the receiver shows a voltage of the order of 0.5... 1 V. Receiver range switch set to the DV position, and the tuning pointer to the frequency of 408 kHz. By rotating the core of the antenna filter circuit, achieve a minimum voltage at the receiver output, while increasing the output voltage of the generator as the signal weakens.
After completing the setup, all adjusted cores of the loop coils and the positions of the magnetic antenna coils must be fixed.
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