A lot of publications are devoted to the design of various radio wave detectors. One of the simplest and most successful designs is described in the publication. However, this design requires the use of a separate dial indicator. If desired, you can use a multimeter instead.
Initially, this design was assembled by the author on the basis of a recording indicator from an old tape recorder, however, the total deflection current of this indicator is measured in hundreds of microamperes, so that the radiation detector worked only in relatively strong fields.
With the use of miniature radio components, this electrical circuit was placed in the plug housing for the radio broadcasting network.
The plug contacts allow you to connect this device to the M890G multimeter. For testing, a simple VHF radio wave generator was used.
This generator is often described as a universal jammer for anything and everything. This is naturally not the case, although at a distance of 1-1.5 m it is quite capable of interfering with the reception of FM radio stations. This circuit captivates with its simplicity, and is quite suitable for educational and demonstration purposes, but nothing more. Here the generator is turned off.
It would seem that with today's abundance of electronic devices surrounding us, when electronics are squeezed even into key fobs and God knows where else, and radios also amaze their abundance, it seems even ridiculous to be interested in this background, and even more so to try to assemble a detector receiver with your own hands. . But it turns out that a lot of people are interested in the detector receiver circuit, this can be understood from the statistics of requests in search engines. In addition, it's not about practicality, but about the "crazy hands" themselves, in the desire to know, understand, do it with your own hands, see (and most importantly, hear!) The result of your creation.
And if you take into account that you can bring a lot of joy to your young children, and even, perhaps, they will show interest in electronics, then there is an incentive to try to join this interesting business. After all, the whole point is that everything is elementary simple, and even a middle school student, as well as a person who knows nothing about electronics, can make a detector receiver! And of course, the coolest thing is that there are NO BATTERIES! And besides this, the whole, so to speak, scheme is assembled from almost nothing. This, of course, seems like a miracle! This can surprise children and adults themselves, too.
The most important factors for louder reception heard in headphones, as you might guess, are the size of the receiving antenna, and also the resistive impedance of the headphones used: the higher their impedance, the better. High-impedance headphones are, of course, rare today (resistance 1600-2200 ohms) and, even if you are very enthusiastic in your search, there is little chance that you will find them. But I have a little trick for you about this, I will share below. This is my know-how, born in my youth, but much later than my visits to the radio circle, where I first got acquainted with the detector radio.
The figure on the left shows a classic detector receiver circuit, which I remember as Our Father from my teenage years when I attended the radio circle in the early 70s of the last century.
We go from left to right according to the scheme: A - antenna, G - ground (ground). L and C1 are an oscillatory circuit, the frequency to which the circuit will be tuned depends on their parameters (values), in other words, which radio station your miracle receiver will receive. Next, the diode D1 (actually, the detector), C2 - a low-pass filter and an earphone T (the classic name in electronics is “telephone”).
Approximate values:
A - wire 0.2-0.5mm PEL, PEV - from 5m or more (farther and higher)
G - heating radiator, plumbing or soil
L - 150-300 turns 0.2-0.3mm (PEL, PEV), coil diameter 60mm (the number of turns is selected or with taps)
D1 - series D2, D9, D18, D20, D310, D311
C1 - variable, 10/200 pF (air or ceramic)
C2 - 2200 - 6800 pF
T - high-resistance telephones for 1600-2200 Ohm (TON-2, TON-2M, TA-4, TA-56, TAG-1, TG-1, etc.)
I think it’s worth taking the D311 diode for the detector, it has Upr \u003d 0.4V. The D310 is already higher - 0.55V. Needed with lower forward voltage. This parameter (Upr) indicates how many volts are dropped across the diode. Those. how much does he lose, in other words. Now, if you select from a bunch of D311 by a milliammeter (the diagram above) with a smaller drop of 4 pieces, then, perhaps, the bridge on them will give a greater signal after straightening.
About the antenna, I think, they understood: further, higher. For me it was a winding wire 0.2-0.4 mm long, 5-10 meters long with a weight attached to the end, which I threw onto the trees directly from my balcony on the 4th floor. 
It is usually advised to wind the inductor on a thick paper frame, but I think this is not important, another insulator will do. The number of turns matters. If you do not find a variable capacitor, you can replace it with a constant one, and fitting to several desired stations can be done by experimental selection of turns. At the same time, make a tap for each station and put a switch. Moreover, it is unlikely that more than 2-3 stations will be received with a satisfactory volume.
You can see (just see, not hear) how radio waves give energy by themselves without amplification, without power, even without any circuit. To do this, you need only one part - the LED. I don’t know how different modern ones are in terms of sensitivity, and even more so in terms of frequency, but I personally tested it on Soviet red AL307 LEDs.
Throw a wire (PEV, PEL) from five meters onto a tree - better, of course, longer and higher. Then master the grounding (water supply, heating). Guess next? One lead of the LED is to the antenna (do not forget to strip the end of the varnished insulation!), the other is to ground (polarity does not matter). That's it, the LED should glow. Certainly not bright.
But if you found high-impedance headphones, then in fact the detector receiver will work without a circuit and without a filter. For a long time I used just such a primitive scheme, as here on the left.
In fact, yes, such a receiver receives absolutely all stations at the same time. But in my place, where I lived then, one radio station dominated strongly, and the rest were almost inaudible. Of course, I experimented with both contours and filters, but did not find any improvement, only a decrease in volume. Therefore, it was precisely such a most primitive, so to speak, scheme that I used. But after my parents bought me a tape recorder, and I connected the circuit to the microphone input, then I already heard another station. It was then that I added a contour and for several more years I recorded rock music while listening to a program that was very popular with us in those years. In those pre-digital times, it was difficult to get high-quality tape recordings of foreign bands, records from speculators cost a lot of money. On the radio, practically only our VIA sounded. This radio program went on for one hour on Sundays and sometimes very cool and, most importantly, new (!) things were broadcast on it. For example, it was from it that I was one of the first to hear and record the composition of The Eagles “Hotel California”, it was the beginning of 1976.
It is also important to say about the quality. In those years, there was still no FM band (it was just emerging), which gave high-quality reception, and even in stereo format. I listened and recorded through my CB detector of course. But if you compare the quality with a conventional receiver and through my detector, this is heaven and earth. Indeed, in conventional receivers, the signal passes through the local oscillator, and I received a “clean” signal through the detector. Therefore, the sound was like directly from a record on a high-quality player. When I let my friends listen, they were amazed at the quality.
So you can also try without a contour first, perhaps you will have one strongly predominant station, and this will suit you.
But there is a hard-to-find part of the receiver, these are, of course, high-impedance phones (headphones). Even in our 70s they were a rarity, and now even more so.
Modern headphones, whatever they are, you can not even try to use. They have a resistance of about several tens of ohms, while the oscillatory circuit of the receiver is of the order of hundreds of kilo ohms. Your headphones will practically be just a conductor in this case, ie. the sound passing through them will be so quiet that it cannot be heard.
What those headphones look like, we look at the picture and remember war films. What is good, their resistance is written on such headphones. So if you suddenly get caught, then you will know the resistance, even without having an ohmmeter at hand.
But if you are not lucky enough to get high-resistance phones even after shoveling the entire local flea market (which is more likely), then next I will describe my personal know-how to you, as promised above.
Know-how is as simple as 2x2. I thought somehow: why not try to transform the signal received from the detector using the most common network transformer for this? Moreover, it is precisely this kind of transformers (made of steel W-shaped plates) that were often used in VLF amplifiers as matching ones. That's what they were called - matching ones, moreover, often at the output, for directly connecting a speaker or headphones from the player.
I think you already understood everything according to the scheme, without even reading it. For these purposes, it is worth choosing among network power transformers that lower the voltage. From the detector, the signal is connected to the network winding, it has the most turns. And the winding intended for power supply is for headphones or a speaker. You can experiment with the secondary winding (more / less) - sound emitters of different models have different resistances: headphones are usually tens of ohms, and speakers are often less than 10 ohms.
ctrl + Enter
Thanks for the help!
The concept of a detector receiver is strongly associated with huge antennas and broadcasting on long and medium waves. In the published article, the author cites experimentally tested schemes of VHF detector receivers designed to listen to the transmissions of VHF FM stations.
The possibility itself detector reception on VHF was discovered quite by accident Once, while walking in the Terletsky park (Moscow, Novogireevo), I decided to listen to the broadcast - fortunately I took with me the simplest loopless detector receiver (it was described in P2001, No. 1, pp. 52, 53, fig. 3) .
The receiver had a telescopic antenna about 1.4 m long. I wonder if reception is possible on such a short antenna? I managed to hear, rather weakly, the simultaneous operation of two stations. But what surprised me was that the reception volume periodically increased and fell almost to zero every 5-7 m, and for each station in different ways!
It is known that in the Far East, and even in the NE, where the wavelength reaches hundreds of meters, this is impossible. I had to stop at the point of maximum reception volume of one of the stations and listen carefully. It turned out - “Radio Nostalgia”, 100.5 FM, broadcasting from nearby Balashikha.
There was no direct line of sight of the antennas of the radio center. How could a FM transmission be received by an amplitude detector? Subsequent calculations and experiments show that this is quite possible and completely independent of the receiver itself.
The simplest portable VHF detector receiver is made in exactly the same way as a field indicator, but instead of a measuring device, you need to turn on high-impedance headphones.
A receiver circuit that meets these requirements is shown in fig. 1 It is very close to the one according to which the receiver mentioned above was made and made it possible to discover the very possibility of detector reception. Only the contour of the VHF band has been added.
Rice. 1. Schematic diagram of the simplest detector VHF receiver.
The device contains a whip telescopic antenna WA1, directly connected to the circuit L1 C1, tuned to the signal frequency. The antenna here is also an element of the circuit, therefore, in order to highlight the maximum signal power, it is necessary to adjust both its length and the tuning frequency of the circuit. In some cases, especially when the antenna length is close to a quarter of the wavelength, it is advisable to connect it to the tap of the contour coil, and select the position of the tap for maximum volume.
Communication with the detector is regulated by a tuning capacitor C2. The detector itself is made on two high-frequency germanium diodes VD1 and VD2. The circuit is completely identical to the voltage doubling rectifier circuit, however, the detected voltage would double only if the coupling capacitor C2 was sufficiently large, but the load on the circuit would be excessive and its quality factor low. As a result, the signal voltage in the circuit and the sound volume would decrease.
In our case, the capacitance of the coupling capacitor C2 is small and the voltage doubling does not occur. For optimal matching of the detector with the circuit, the capacitance of the coupling capacitor should be equal to the geometric mean between the input resistance of the detector and the resonant resistance of the circuit. Under this condition, the maximum power of the high-frequency signal, corresponding to the maximum loudness, is given to the detector.
Capacitor C3 - blocking it closes the high-frequency components of the current at the output of the detector. The load of the latter are telephones with a direct current resistance of at least 4 kOhm. The entire receiver is assembled in a small metal or plastic case. A telescopic antenna with a length of at least 1 m is fixed in the upper part of the case, and a connector or jacks for connecting telephones is fixed at the bottom. Note that the telephone cord serves as the second half of the receiving dipole, or counterbalance
Coil L1 is frameless, it contains 5 turns of PEL or PEV wire with a diameter of 0.6-1 mm, wound on a mandrel with a diameter of 7 ... 8 mm. You can select the required inductance by stretching or compressing the turns during tuning.
A variable capacitor (KPE) C1 is best used with an air dielectric, for example, type 1KPVM with two or three movable and one or two fixed plates. Its maximum capacitance is small and can be 7-15 pF. If there are more plates (respectively, the capacitance is larger), it is advisable either to remove some of the plates, or to connect a constant or trimmer capacitor in series with the KPI, thus reducing the maximum capacitance. As C1, small-sized “smooth tuning” capacitors from transistor receivers with a HF range are also suitable.
Capacitor C2 - ceramic trimmer, type KPK-1 or KPK-M with a capacity of 2 ... 7 pF It is permissible to use other trimmer capacitors, as well as install a KPI similar to C1 by bringing its handle to the receiver panel. This will allow you to adjust the connection “on the go”, optimizing reception
Diodes VD1 and VD2, in addition to those indicated in the diagram, can be types GD507B, D18, D20. Blocking capacitor C3 is ceramic, its capacitance is non-critical and can range from 100 to 4700 pF.
Setting up the receiver is easy and comes down to tuning the circuit with capacitor C1 to the frequency of the station and adjusting the connection with capacitor C2 until the maximum volume is obtained. In this case, the contour setting will inevitably change, so all operations must be carried out sequentially several times, while choosing the best place for reception.
By the way, it does not necessarily have to coincide (and most likely will not) with the place where the field strength is maximum. This should be discussed in more detail and finally explained why this receiver can receive FM signals at all.
If the L1C1 circuit of our receiver is adjusted so that the carrier of the FM signal falls on the slope of the resonant curve, then the FM will be converted to AM. Let's see what the quality factor of the circuit should be for this. Assuming the loop bandwidth to be equal to twice the frequency deviation, we obtain Q = fo/2*f = 700 for both the upper and lower VHF bands.
The real quality factor of the circuit in the detector receiver will probably be lower due to the low intrinsic quality factor (of the order of 150...200) and shunting of the circuit by both the antenna and the input impedance of the detector. However, a slight FM to AM conversion is possible, and thus the receiver will barely work if its circuit is slightly detuned up or down in frequency.
However, there is a much more powerful factor that contributes to the transformation of FM into AM - this is interference. Very rarely, the receiver is in the line of sight of the radio station antenna, more often it is covered by buildings, hills, trees and other reflective objects. Several beams scattered by these objects arrive at the receiver antenna.
Even in the line of sight, in addition to the direct beam, several reflected ones come to the antenna. The total signal depends on both the amplitudes and the phases of the summing components.
Two signals are added if they are in phase, that is, their path difference is a multiple of an integer number of wavelengths, and subtracted if they are out of phase, when their path difference is the same number of wavelengths plus half a wavelength. But after all, the wavelength, like the frequency, changes with the FM! Both the path difference of the rays and their relative phase shift will change. If the path difference is large, then even a small change in frequency leads to significant phase shifts. An elementary geometric calculation leads to the relation:
where, delta t is the difference in the path of the rays required for a phase shift of ± Pi/2, i.e., to obtain the full AM of the total signal; tdeltaf - frequency deviation. By total AM here we mean the change in the amplitude of the total signal from the sum of the amplitudes of two signals to their difference. The formula can be further simplified if we consider that the product of frequency and wavelength fo*(lambda) is equal to the speed of light c; delta t = c/4*delta f.
Then, in one period of the modulating sound oscillation, the total amplitude of the interfering signal will pass through the maxima and minima several times, and the distortions during the conversion of FM to AM will be extremely strong, up to the complete illegibility of the audio signal when received on the AM detector.
It is always better to use a directional antenna as it increases the direct signal and attenuates the reflected signals coming from other directions.
Only in our case of the simplest detector receiver did interference play a useful role and made it possible to listen to the transmission, but the transmission can be heard weakly or with great distortion not everywhere, but only in certain places. This explains the periodic changes in the volume of reception in Terletsky Park.
A radical way to improve reception is to use a frequency detector instead of an amplitude one. On fig. 2 shown diagram of a portable detector VHF receiver with a simple frequency detector, made on a single high-frequency germanium transistor UT1.
The use of a germanium transistor is due to the fact that its junctions open at a threshold voltage of about 0.15 V, which makes it possible to detect rather weak signals. The junctions of silicon transistors open at a voltage of about 0.5 V, and the sensitivity of the receiver with a silicon transistor is much lower.
Rice. 2. Detector VHF receiver with a frequency detector.
As in the previous design, the antenna is connected to the input circuit L1C1, tuned to the signal frequency using KPI C1. The signal from the input circuit is fed to the base of the transistor. Another one is inductively connected to the input circuit - L2C2, which is also tuned to the signal frequency.
The oscillations in it, due to inductive coupling, are shifted in phase by 90 ° relative to the oscillations in the input circuit. From the tap of the coil L2, the signal is fed to the emitter of the transistor. The blocking capacitor C3 and high-resistance telephones BF1 are included in the collector circuit of the transistor.
The transistor opens when positive half-waves of the signal act on its base and emitter, and the instantaneous voltage at the emitter is greater. At the same time, a detected and smoothed current passes through the telephones in its collector circuit. But the positive half-waves overlap only partially when the oscillation phases in the circuits are shifted by 90°, so the detected current does not reach the maximum value determined by the signal level.
With FM, depending on the frequency deviation, the phase shift also changes, in accordance with the phase-frequency characteristic (Ф4Х) of the L2С2 circuit. When the frequency deviates to one side, the phase shift decreases and the half-waves of the signals at the base and emitter overlap more, as a result of which the detected current increases.
When the frequency deviates to the other side, the overlap of the half-waves decreases and the current drops. This is how frequency signal detection occurs.
The detector transfer coefficient directly depends on the quality factor of the L2C2 circuit, it should be as high as possible (in the limit, as we calculated, up to 700), which is why the connection with the emitter circuit of the transistor is chosen weak. Of course, such a simple detector does not suppress the AM of the received signal; moreover, its detected current is proportional to the signal level at the input, which is an obvious disadvantage. The justification lies only in the exceptional simplicity of the detector.
Just like the previous one, the receiver is assembled in a small case, from which a telescopic antenna extends upwards, and telephone jacks are located below. The handles of both KPIs are displayed on the front panel. These capacitors should not be combined into one unit, since, by tuning them separately, it is possible to obtain both greater volume and better reception quality.
The receiver coils are frameless, they are wound with PEL 0.7 wire on a mandrel with a diameter of 8 mm. L1 has 5 turns and L2 has 7 turns tapped from the 2nd turn, counting from the ground terminal. If possible, it is advisable to wind the L2 coil with a silver-plated wire to increase its quality factor, while the wire diameter is not critical.
The inductance of the coils is selected by squeezing and stretching the turns so that the well-audible VHF stations are in the middle of the tuning range of the corresponding KPI. The distance between the coils within 15 ... 20 mm (the axes of the coils are parallel) is selected by bending their leads soldered to the KPI.
With the described receiver, you can conduct a lot of entertaining experiments, exploring the possibility of detector reception on VHF, the features of the passage of waves in urban areas, etc. Experiments to further improve the receiver are not excluded.
However, the sound quality when receiving high-impedance headphones with tin membranes leaves much to be desired. In connection with the above, a more advanced receiver has been developed that provides better sound quality and allows the use of various outdoor antennas connected to the receiver by a feed line.
While experimenting with a simple detector receiver, we repeatedly had to make sure that the power of the detected signal is high enough (tens and hundreds of microwatts) and could provide rather loud operation of telephones.
But the reception turns out to be unimportant due to the lack of a frequency detector (FR). The second receiver (Fig. 2) solves this problem to some extent, but the signal power is also inefficiently used in it due to the quadrature power supply of the transistor by high-frequency signals. Therefore, it was decided to use two detectors in the receiver: amplitude - to power the transistor; frequency - for better signal detection
The scheme of the developed receiver is shown in fig. 3. The external antenna (loop dipole) is connected to the receiver by a two-wire line made of a VHF ribbon cable with a wave impedance of 240.300 Ohm. Matching the cable with the antenna is obtained automatically, and matching with the input circuit L1C1 is achieved by selecting the connection point for the tap to the coil.
Generally speaking, an unbalanced connection of the feeder to the input circuit reduces the noise immunity of the antenna-feeder system, but, given the low sensitivity of the receiver, this does not really matter here.
There are well-known ways to symmetrically connect a feeder using a coupling coil or balancing transformer. Under the conditions of the author, the loop dipole was made of a conventional insulated mounting wire and placed on a balcony, in a place with a maximum field strength. The length of the feeder did not exceed 5 m. With such insignificant lengths, the losses in the feeder are negligible, so a telephone wire can be successfully used.
The input circuit L1C1 is tuned to the signal frequency, and the high-frequency voltage released on it is rectified by an amplitude detector made on a high-frequency diode VD1. Since the oscillation amplitude is unchanged during FM, there are practically no requirements for smoothing the rectified DC voltage.
Rice. 3. Scheme of a VHF receiver powered by field energy.
The quadrature frequency response of the receiver is assembled on a transistor VT1 and a phase-shifting circuit L2C2. A high-frequency signal is supplied to the base of the transistor from the coil tap of the input circuit through the coupling capacitor C3, and to the emitter - from the coil tap of the phase-shifting circuit. The detector works exactly the same as in the previous design.
To increase the transmission coefficient of the black hole and make better use of the amplifying properties of the transistor, a bias was applied to its base through the resistor R1, which is why it was necessary to install a decoupling capacitor C3. Pay attention to its significant capacitance - it was chosen as such for shorting low-frequency currents to the emitter, i.e., for “grounding” the base at audio frequencies. This increases the gain of the transistor and increases the volume of the reception.
The primary winding of the output transformer T1 is included in the collector circuit of the transistor, which serves to match the high output resistance of the transistor with the low resistance of telephones. The receiver can be used with high-quality stereo phones TDS-1 or TDS-6. Both phones (left and right channels) are connected in parallel.
Capacitor C5 is a blocking capacitor, it serves to close high-frequency currents penetrating into the collector circuit. The SB1 button is used to close the collector circuit when setting the input circuit and searching for a signal. At the same time, the sound in the phones disappears, but the sensitivity of the indicator increases significantly.
The design of the receiver can be very different, but you need a front panel with KPI C1 and C2 installed on it (they are equipped with separate tuning knobs) and an SB1 button. So that the movements of the hands do not affect the adjustment of the contours, it is desirable to make the panel metal or from foil material.
It can also serve as a common wire of the receiver. KPI rotors must have good electrical contact with the panel. Antenna and telephone connectors X1 and X2 can be installed both on the same front panel and on the side or rear walls of the receiver housing. Its dimensions entirely depend on the details available. Let's say a few words about them.
Capacitors C1 and C2 are of the KPV type with a maximum capacitance of 15.25 pF. Capacitors C3-C5 are ceramic, small-sized.
Coils L1 and L2 are frameless, wound on mandrels with a diameter of 8 mm and contain 5 and 7 turns, respectively. Winding length 10 ... 15 mm (adjust when setting).
PEL wire 0.6 ... 0.8 mm, but it is better to use silver-plated, especially for the L2 coil. The taps are made from 1 turn to the transistor electrodes and from 1.5 turns to the antenna.
Coils can be arranged both coaxially and parallel to each other. The distance between the coils (10 ... 20 mm) is selected during adjustment. The receiver will work even in the absence of inductive coupling between the coils - capacitive coupling through the interelectrode capacitance of the transistor is quite enough. Transformer T1 is taken ready, from the broadcast loudspeaker.
As VT1, any germanium transistor with a cutoff frequency of at least 400 MHz is suitable. When using a p-p-p transistor, for example, GT313A, the polarity of turning on the dial indicator and the diode should be reversed. The diode can be any germanium, high-frequency.
Any indicator with a total deflection current of 50-150 μA is suitable for the receiver, for example, a dial indicator of the recording level from a tape recorder.
Setting up the receiver comes down to tuning the circuits to the frequencies of well-audible radio stations, selecting the position of the coil taps for maximum volume and reception quality, as well as the connection between the coils. It is useful to choose the resistor R1, also at maximum volume.
With the described antenna on the balcony, the receiver provided high-quality reception of the two stations with the most powerful signal at a distance of at least 4 km from the radio center and in the absence of direct visibility (blocked at home). The collector current of the transistor was 30...50 μA.
Of course, the possible designs of detector VHF receivers are not limited to those described. On the contrary, they should be considered only as the first experiments in this interesting direction. If you use an efficient antenna placed on the roof and directed to the radio station of interest, you can get sufficient signal strength even at a considerable distance from the radio station.
This opens up very attractive prospects for high-quality headphone reception, and in some cases it may be possible to get loud-speaking reception as well. Improvement of the receivers themselves is possible with the use of more efficient detection circuits and high-quality volumetric, in particular, spiral resonators, as oscillatory circuits.
V. Polyakov, Moscow. R2001, 7.
I assembled a prototype detector VHF FM / FM receiver according to the scheme of V. Polyakov (see Fig. 3).
As can be easily seen from Fig. 3, there is no battery of galvanic cells on the device diagram - which means that the device is powered by radio wave energy, torsion fields, free energy, near-Earth ethereal vortices, Tesla generator, holy spirit (underline as necessary, based on your religious beliefs).As a pointer indicator, a 50 μA recording level indicator from an antique tape recorder was used. Telescopic antenna, 70 cm. As a counterweight, a vertically hanging stranded wire of the same length is used, clinging to the "mass" with a crocodile.
Small-sized network transformer for 220/6 volts. At the same time, I checked whether TVZ is so good, as I promoted it earlier :) It turned out that the playback volume does not subjectively depend on the dimensions of the transformer (with the same transformation ratio). The only thing is that with a decrease in the number of turns of the primary, a blockage appears in the low frequencies.
With variable low-capacity capacitors, it’s very bad: I found only one with an air dielectric, the second had to be installed with a tuning ceramic one.
Receiver setting: press the SB1 button and adjust C1 to achieve the maximum readings of the PA1 indicator. Release the button and by tuning C2 will tune in to the station.
The test results were encouraging.
I checked at two points: on the 10th floor of an office building (line of sight to the TV tower, distance 300 m) and on a pedestrian bridge (line of sight, about 2 km). In the building, the signal is not very strong (the arrow of the field indicator has deviated by a quarter of the scale), reinforced concrete walls are affecting. On the bridge, the signal is surprisingly loud, you get the feeling that you are listening to the player. The indicator needle goes off scale. A change in signal strength was noted up to the termination of reception every few meters.
There was an attempt to receive a signal on a road bridge with a direct line of sight to the transmitter (4 km), but the power was not enough for the FM detector to work (the arrow barely deviated).
In all cases, the 1st channel of the Ukrainian radio (TRK "Era") was received. Unfortunately, it has not yet been possible to receive my beloved Radio Chanson: (((, apparently due to the high inductance of the coils and my complete ignorance of the geographical location of commercial FM stations in our city. In the near future, the coils are threatened with rewinding, transmitters - - declassification, and new tests for the receiver.
Stay in touch!
Appearance of the device:
Source:
Magazine "Radio" No. 7, 2002, pp. 54-56, "Detector VHF receivers."
I know at least two places from which local FM radio stations are broadcast:
1. Institute of Geological Exploration (nine-story "candle" on Shchorsa 12) - it may well be that this is just Chanson. :) Although I don’t know for sure (I once knew, but I forgot :)).
2. The Druzhba cinema building - earlier Unison radio (somehow it was called that) started its activities there, they rented a whole floor there, I even saw a transmitter in their rack. :-P But they have been bent for a long time and instead of them there, it seems like, another radio station works. For some reason I think that this is MFM, but of course I'm wrong. ;)
Oh, thanks for the tip on the geologists!
As for Druzhba, these radio operators were at one time our office neighbors, but have now moved out. When everything worked for them, the radio was well listened to in the speakers of the company.
War, I think you are ready to create your own FM radio station. I advise you to do this as soon as possible, because in my person you will find the most talented enthusiast for conducting musical, humorous, erotic, sports and political broadcasts.
It's just that since I saw Ali G's film, I secretly dream of creating an underground radio station where the problems of criminal Negro ghettos would be spoken through our lips.
I hope it will be a pirate radio?
In general, if you seriously get confused by this issue, then you can buy such a device, since the price is lifting: http://urlab.narod.ru/
And here are some more links
A. Pakhomov, Zernograd, Rostov region
Radio, 2003, No. 1
Comparison of modern imported radios (mostly Chinese-Hong Kong) with domestic past production years leads to interesting results. In the ranges of SV, DV and KB, the quality indicators of old domestic receivers are much better. Thus, the dual-band "QUARTZ-302", manufactured in the late 80s, had a real sensitivity of 0.4 mV / m, which is unattainable for imported analogues, excluding, of course, expensive digital and professional models. The parameters of the receivers of those years were subject to the domestic GOST 5651-82, which strictly normalized the sensitivity, selectivity and other characteristics depending on the complexity group (class).
Without going into a detailed analysis of the electrical path, we only note that modern small-sized radio receivers are produced mainly in a vertical design, in which the small horizontal size of the radio receiver does not allow placing a magnetic antenna (MA) of sufficient length. With an MA length of only a few centimeters, the signal level at the input of the first stage is low, and the signal-to-noise ratio is poor. As a result, outwardly attractive and seemingly comfortable "Tecsan", "Manbo", etc. in the medium wave range are very "noisy" and do not provide an acceptable reception quality. In the VHF band, the performance is somewhat better, but even here only local reception is possible with good quality. Due to the characteristics of the propagation of radio waves in this range and the low efficiency of the whip antenna, the VHF band (on the receiver it is designated as FM) is often useless at a considerable distance from the transmitting centers. Under these conditions, it is much more expedient to have an old MW-LW-HF receiver, having upgraded it according to the method proposed below.
A favorable feature of modern radios is the power supply from two finger-type batteries with a total voltage of 3 V. Domestic models worked mainly from the Krona nine-volt battery. The advantages of a three-volt power supply are obvious: the capacity of AA type galvanic cells (domestic version - size 316) is several times higher, and the cost of even two pieces is lower than one Krona battery and its analogues. The service life of the latter at an average sound volume does not exceed 20 ... 30 hours. Due to the owner's understandable reluctance to frequently change an expensive battery, quite serviceable domestic radios lie idle. Alternative power options also have disadvantages: batteries are expensive and require periodic charging, and mains power negates portability, a major advantage of pocket radios.
The way out is to transfer the receiver to a three-volt battery supply. One way to do this is suggested in . It consists in using the conversion of the voltage of the AA elements to the receiver supply voltage of 9 V. However, this does not completely eliminate interference. The best and, perhaps, the easiest way is to make changes to the circuit of the radio itself in such a way as to ensure the normal operation of all stages at a supply voltage of 3 V. This is quite possible, and with a competent approach, the receiver parameters (except output power) practically do not deteriorate.
Let's consider modernization on the example of the "QUARTZ-302" receiver. Its circuit is typical for the receivers of this group and is shown in Fig. 1 (it does not show the elements of MA, input circuits and local oscillator circuits, which are not touched at all during refinement). In later models of this and other radio receivers, instead of FSS on inductors, a piezo filter was used, which, however, does not affect the further refinement technology, as well as other minor differences in the circuits of transistor receivers.
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The first stage on the transistor VT1 is a mixer with a combined local oscillator. The mode of the transistor VT1 is set by a base bias through the resistor R2 and is stabilized by power supply from the parametric stabilizer VD1, R11, C22. The stabilization voltage is 1.44 V, in connection with which it is possible to maintain it when the total supply voltage is reduced to 2 ... 3 V. To do this, it is enough to reduce the resistance of the ballast resistor R11 to 1 kOhm.
It is important to note that the first stage largely determines the operation of the receiver as a whole. Transistor VT1 type KT315 is not optimal here: it has a high noise level, significant transition capacitance and low gain. Much better results are obtained with microwave transistors of the KT368, KT399A types. Although their parameters are normalized at higher frequencies, the noise minimum area extends "down", up to a frequency of 0.5 MHz (KT399A) - 0.1 MHz (KT368), i.e., it also captures the MW range. The gain of these transistors is less dependent on the supply voltage, which is also important in this case. The author used the KT399A transistor, while the noise level turned out to be so low that in the absence of tuning to the station it is even difficult to determine whether the receiver is on or off. Thus, replacing the transistor VT1 guarantees an increase in sensitivity, limited by noise. To ensure the normal operation of the local oscillator (at an emitter current of about 1 mA), the resistances of the resistors R3 and R5 should be reduced to 620 Ohm and 1.5 kOhm, respectively.
In the original circuit, the RF-IF path and the first UZCH stage are fed through the R10C13 decoupling filter. A voltage drop of about 1 V is formed across the resistor R10, which is undesirable. To avoid voltage losses, the R10 resistor should be replaced with a small-sized DPM-3 choke from unified TV blocks of the 3rd and 4th generations or, in extreme cases, just a wire jumper. True, in the latter case, the absence of self-excitation when the batteries are discharged is not guaranteed.
In the IF path, it is highly desirable to replace the VT3 transistor of the KT315B type with KT3102E, KT3102D or KT342B, KT342V with a gain of 400 ... 500. This is necessary in order to increase the IF gain and thus maintain the gain limited sensitivity, as well as to ensure the effective operation of the AGC. The signal of the latter through the filter R13C23 is fed to the base of the transistor VT3, and therefore it is important to correctly set its operating point by reducing the resistance of the resistor R12 to 30 kOhm.
In UMZCH, it is also necessary to reduce the resistance of the resistor R8 to 39 kOhm, and bring the total resistance of two resistors R21, R23 connected in parallel to 1 ... 1.5 Ohm. Why replace the resistors R21, R23 with one wire resistor of the specified resistance. This UMZCH provides for adjusting the quiescent current with a tuning resistor R16. To avoid distortion and obtain acceptable efficiency, the quiescent current should be within 5 ... 7 mA.
For the battery, a shell with spring contacts is made, into which two AA elements should fit tightly. The design of the shell can be any, in the author's version it is made of double-sided foil fiberglass and tin, the parts are connected by soldering. The dimensions of the shell allow it to be placed in the Krona battery compartment.
The receiver is tuned with a fresh battery, the voltage under load of which is at least 3 V. First, you should check the operating modes of all stages: for transistors VT1-VT3, voltage measurements are taken at their collectors, for transistors VT4-VT7 - at emitters (see table) . In practice, it may be necessary to adjust the mode of the transistor VT3, the voltage on the collector of which in the absence of a signal should be 1.4 ... 1.6 V and be regulated by the selection of resistor R12. The remaining modes are usually set automatically if the above operations are observed.
Further, if possible, a signal from the 3H generator is fed to the input of the UMZCH (VT2) and, observing the output signal on the oscilloscope, by selecting the resistor R8, the symmetry of the half-wave sinusoid is achieved, and by the resistor R16 - the absence of "step" type distortion. Then measure the total current consumption in silent mode, which should be 10 mA, and, if necessary, adjust it with a tuning resistor R16.
As can be seen, the proposed modernization is simple and does not require large expenditures of time and money. The achieved result is impressive - the sensitivity of the receiver does not decrease (and even increases slightly), the selectivity remains the same, the maximum current consumption at signal peaks does not exceed 20 mA, the performance is maintained when the supply voltage is reduced to 1.8 V, the life of the radio receiver from one set of elements AA - at least 80 hours, and with good quality of the latter - more than 100 hours.
The only parameter that deteriorates during rework is the output sound power, which drops to 20 ... 30 mW. As a rule, this is quite enough, since the characteristic sensitivity of the BA1 head is very high. The majority of imported receivers have the same output power, but subjectively the sound quality of the converted one is better due to the better acoustic properties of the case.
If desired, modernization can be continued by assembling a more powerful UMZCH bridge. In this case, one should not "reinvent the wheel" and manufacture it on discrete elements, although such schemes have been published. There is a large range of specialized microcircuits - ready-made high-quality amplifiers with low-voltage power supply. Figure 2 shows a diagram of one of them - UMZCH on the TRA301 chip. Here are some of its characteristics: output power at a supply voltage of 3.3 V, KHi = 0.5%, F = 1 kHz, RH = 8 Ohm - 250 mW; quiescent current - less than 1.5 mA; the width of the reproducible frequency band at maximum output power is 10 kHz.
Monoamplifiers based on TRA311, TRA701, TRA711 microcircuits have similar parameters and switching circuits. All microcircuits are equipped with protection against thermal and electrical overloads. A typical scheme for their inclusion with the necessary additional surface-mounted elements makes it possible to manufacture a new amplifier in the form of a miniature block. The old UMZCH is dismantled, leaving only the preamplification stage on the VT2 transistor, and the new one is assembled by surface (or any) mounting on a separate board according to the diagram in Fig. 2 of . The board is mounted on brackets to the main board in the place where the previous UMZCH was dismantled. The input signal is supplied from the collector of the transistor VT2 (see Fig. 1), plus the power supply from the battery, the capacitance of the capacitor C31 is increased to 220 microfarads. The integrated UMZCH does not require settings. It may only be necessary to adjust the pre-amplification stage on the transistor VT2 according to the collector voltage indicated in the table by selecting the resistor R8.
LITERATURE
