Receiver with 1.5 volt power supply. Super-generative transistor VHF receivers with low-voltage power supply (1.5V)

Radio

A previously home-made simple loud-speaking radio receiver with a low-voltage power supply of 0.6-1.5 Volts is idle. The Mayak radio station on the CB band went silent and the receiver, due to its low sensitivity, did not receive any radio stations during the day. During the modernization of a Chinese radio, the TA7642 chip was discovered. This transistor-like chip houses the UHF, detector, and AGC system. By installing a ULF radio in a single transistor circuit, you get a highly sensitive loud-speaking direct amplification radio receiver powered by a 1.1-1.5 Volt battery.

How to make a simple radio with your own hands

The radio circuit is specially simplified for repetition by novice radio designers and is configured for long-term operation without shutdown in energy-saving mode. Let's consider the operation of a simple direct amplification radio receiver circuit. Look at the photo.

The radio signal induced on the magnetic antenna is supplied to input 2 of the TA7642 chip, where it is amplified, detected and subjected to automatic gain control. Power supply and pickup of the low-frequency signal is carried out from pin 3 of the microcircuit. A 100 kOhm resistor between the input and output sets the operating mode of the microcircuit. The microcircuit is critical to the incoming voltage. The gain of the UHF microcircuit, the selectivity of radio reception over the range and the efficiency of the AGC depend on the supply voltage. The TA7642 is powered through a 470-510 Ohm resistor and a variable resistor with a nominal value of 5-10 kOhm. Using a variable resistor, the best operating mode for the receiver in terms of reception quality is selected, and the volume is also adjusted. The low frequency signal from the TA7642 is supplied through a 0.1 µF capacitor to the base of the n-p-n transistor and is amplified. A resistor and capacitor in the emitter circuit and a 100 kOhm resistor between the base and collector set the operating mode of the transistor. In this embodiment, the output transformer from a tube TV or radio was specifically selected as the load. The high-resistance primary winding, while maintaining acceptable efficiency, sharply reduces the current consumption of the receiver, which will not exceed 2 mA at maximum volume. If there are no requirements for efficiency, you can include a loudspeaker with a resistance of ~30 Ohms, telephones or a loudspeaker into the load through a matching transformer from a transistor receiver. The loudspeaker in the receiver is installed separately. The rule will work here: the larger the loudspeaker, the louder the sound; for this model, a speaker from a widescreen cinema was used :). The receiver is powered by one 1.5 Volt AA battery. Since the country radio receiver will be operated away from powerful radio stations, provision is made for the inclusion of an external antenna and grounding. The signal from the antenna is supplied through an additional coil wound on a magnetic antenna.

Details on the board

Five splat pins

Chassis board

Back wall

The housing, all elements of the oscillating circuit and the volume control are taken from a previously built radio receiver. See details, dimensions and scale template. Due to the simplicity of the circuit, no printed circuit board was developed. Radio parts can be installed by hand using a surface-mounted installation or soldered on a small area of ​​a breadboard.

Tests have shown that a receiver at a distance of 200 km from the nearest radio station with a connected external antenna receives 2-3 stations during the day, and up to 10 or more radio stations in the evening. Watch a video. The content of evening radio broadcasts costs the production of such a receiver.

The contour coil is wound on a ferrite rod with a diameter of 8 mm and contains 85 turns, the antenna coil contains 5-8 turns.

As stated above, the receiver can easily be replicated by a novice radio designer.

Do not rush to immediately buy the TA7642 microcircuit or its analogues K484, ZN414. The author found the microcircuit in radio receiver costing 53 rubles))). I admit that such a microcircuit can be found in some broken radio or player with the AM band.

In addition to its direct purpose, the receiver works around the clock as a simulator of the presence of people in the house.

What is a superregenerator, how does it work, what are its advantages and disadvantages, in what amateur radio designs can it be used? This article is devoted to these issues. A super-regenerator (also called a super-regenerator) is a very special type of amplification, or amplification-detector device, which, despite its exceptional simplicity, has unique properties, in particular, a voltage gain of up to 105...106, i.e. reaching a million!

This means that sub-microvolt input signals can be amplified to sub-volts. Of course, it is impossible to obtain such amplification in one stage in the usual way, but a completely different method of amplification is used in the superregenerator. If the author is allowed to philosophize a little, then we can say, not quite strictly, that super-regenerative enhancement occurs in other physical coordinates. Conventional amplification is carried out continuously in time, and the input and output of the amplifier (four-port network), as a rule, are separated in space.

This does not apply to two-terminal amplifiers, for example, a regenerator. Regenerative amplification occurs in the same oscillating circuit to which the input signal is applied, but again continuously in time. The superregenerator works with samples of the input signal taken at certain points in time. Then the sampling is amplified over time, and after a certain period the output amplified signal is removed, often even from the same terminals or sockets to which the input is connected. While the amplification process is in progress, the superregenerator does not respond to input signals, and the next sample is made only when all amplification processes are completed. It is this principle of amplification that allows one to obtain huge coefficients; the input and output do not need to be decoupled or shielded - after all, the input and output signals are separated in time, so they cannot interact.

The super-regenerative method of amplification also has a fundamental drawback. In accordance with the Kotelnikov-Nyquist theorem, for undistorted transmission of the signal envelope (modulating frequencies), the sampling frequency must be at least twice the highest modulation frequency. In the case of an AM broadcast signal, the highest modulating frequency is 10 kHz, an FM signal is 15 kHz and the sampling frequency must be at least 20...30 kHz (we are not talking about stereo). The bandwidth of the superregenerator is almost an order of magnitude larger, i.e. 200...300 kHz.

This drawback cannot be eliminated when receiving AM signals and was one of the main reasons for the displacement of superregenerators by more advanced, albeit more complex, superheterodyne receivers, in which the bandwidth is equal to twice the highest modulating frequency. Oddly enough, during the World Cup the described disadvantage manifests itself to a much lesser extent. FM demodulation occurs at the slope of the superregenerator resonance curve - FM is converted into AM and then detected. In this case, the width of the resonance curve should be no less than twice the frequency deviation (100...150 kHz) and a much better matching of the bandwidth with the width of the signal spectrum is obtained.

Previously, superregenerators were performed using vacuum tubes and became widespread in the middle of the last century. At that time there were few radio stations on the VHF band, and wide bandwidth was not considered a particular disadvantage, in some cases even making it easier to tune in and search for rare stations. Then super-regenerators using transistors appeared. Now they are used in radio control systems for models, security alarms, and only occasionally in radio receivers.

Super-regenerator circuits differ little from regenerator circuits: if the latter periodically increases the feedback to the generation threshold, and then reduces it until the oscillations stop, then a super-regenerator is obtained. Auxiliary damping oscillations with a frequency of 20...50 kHz, which periodically change the feedback, are obtained either from a separate generator or arise in the highest frequency device (super-regenerator with self-quenching).

Basic diagram of a regenerator-superregenerator

To better understand the processes occurring in the superregenerator, let us turn to the device shown in Fig. 1, which, depending on the time constant of the R1C2 chain, can be both a regenerator and a super-regenerator.

Rice. 1 Super regenerator.

This scheme was developed as a result of numerous experiments and, as it seems to the author, is optimal in terms of simplicity, ease of setup and the results obtained. Transistor VT1 is connected according to the circuit of a self-oscillator - an inductive three-point. The generator circuit is formed by coil L1 and capacitor C1, the coil tap is made closer to the base pin. In this way, the high output resistance of the transistor (collector circuit) is matched with a lower input resistance (base circuit). The transistor's power supply circuit is somewhat unusual - the constant voltage at its base is equal to the collector voltage. A transistor, especially a silicon one, can easily operate in this mode, because it opens at a voltage at the base (relative to the emitter) of about 0.5 V, and the collector-emitter saturation voltage is, depending on the type of transistor, 0.2...0 ,4 V. In this circuit, both the collector and the DC base are connected to a common wire, and power is supplied through the emitter circuit through resistor R1.

In this case, the voltage at the emitter is automatically stabilized at 0.5 V - the transistor operates like a zener diode with the specified stabilization voltage. Indeed, if the voltage at the emitter drops, the transistor will close, the emitter current will decrease, and after this the voltage drop across the resistor will decrease, which will lead to an increase in the emitter voltage. If it increases, the transistor will open stronger and the increased voltage drop across the resistor will compensate for this increase. The only condition for the correct operation of the device is that the supply voltage must be noticeably higher - from 1.2 V and higher. Then the transistor current can be set by selecting resistor R1.

Let's consider the operation of the device at high frequencies. The voltage from the lower (according to the diagram) part of the turns of coil L1 is applied to the base-emitter junction of transistor VT1 and is amplified by it. Capacitor C2 is a blocking capacitor; for high frequency currents it has low resistance. The load in the collector circuit is the resonant resistance of the circuit, somewhat reduced due to the transformation by the upper part of the coil winding. When amplified, the transistor inverts the phase of the signal, then it is inverted by a transformer formed by parts of the L1 coil - phase balance is performed.

And the balance of amplitudes necessary for self-excitation is obtained with sufficient gain of the transistor. The latter depends on the emitter current, and it is very easy to regulate by changing the resistance of resistor R1, for example, by connecting, for example, two resistors in series, constant and variable. The device has a number of advantages, which include simplicity of design, ease of setup and high efficiency: the transistor consumes exactly as much current as is necessary to sufficiently amplify the signal. The approach to the generation threshold turns out to be very smooth, moreover, the adjustment occurs in the low-frequency circuit, and the regulator can be moved from the circuit to a convenient place.

The adjustment has little effect on the circuit tuning frequency, since the transistor supply voltage remains constant (0.5 V), and therefore the interelectrode capacitances almost do not change. The described regenerator is capable of increasing the quality factor of circuits in any wave range, from DV to VHF, and coil L1 does not have to be a circuit coil - it is permissible to use a coupling coil with another circuit (capacitor C1 is not needed in this case).

You can wind such a coil on the rod of the magnetic antenna of a DV-MW receiver, and the number of turns should be only 10-20% of the number of turns of the loop coil; a Q-multiplier on a bipolar transistor is cheaper and simpler than on a field-effect transistor. The regenerator is also suitable for the HF range if you connect the antenna to circuit L1C1 either with a coupling coil or with a low-capacity capacitor (up to fractions of a picofarad). The low-frequency signal is removed from the emitter of transistor VT1 and fed through a separating capacitor with a capacity of 0.1...0.5 μF to the AF amplifier.

When receiving AM stations, such a receiver provided a sensitivity of 10...30 μV (feedback below the generation threshold), and when receiving telegraph stations on beats (feedback above the threshold) - units of microvolts.

Processes of rise and fall of oscillations

But let's return to the super-regenerator. Let the supply voltage be supplied to the described device in the form of a pulse at time t0, as shown in Fig. 2 on top.

Rice. 2 Oscillations.

Even if the transistor gain and feedback are sufficient for generation, oscillations in the circuit will not occur immediately, but will increase exponentially for some time τn. According to the same law, the decay of oscillations occurs after the power is turned off; the decay time is designated as τс.

Rice. 3 Oscillatory circuit.

In general, the law of rise and fall of oscillations is expressed by the formula:

Ucont = U0exp(-rt/2L),

where U0 is the voltage in the circuit from which the process began; r is the equivalent loss resistance in the circuit; L is its inductance; t - current time. Everything is simple in the case of a decline in oscillations, when r = rп (loss resistance of the circuit itself, rice. 3). The situation is different when oscillations increase: the transistor introduces negative resistance into the circuit - roc (feedback compensates for losses), and the total equivalent resistance becomes negative. The minus sign in the exponent disappears, and the law of growth will be written:

cont = Uсexp(rt/2L), where r = roс - rп

From the above formula, you can also find the rise time of the oscillations, taking into account that the growth begins with the signal amplitude in the circuit Uc and continues only to the amplitude U0, then the transistor enters the limiting mode, its gain decreases and the amplitude of the oscillations stabilizes: τн = (2L/r) ln(U0/Uc).

As we can see, the rise time is proportional to the logarithm of the reciprocal of the level of the received signal in the circuit. The larger the signal, the shorter the rise time. If power pulses are applied to the superregenerator periodically, with a superization (quenching) frequency of 20...50 kHz, then flashes of oscillations will occur in the circuit (Fig. 4), the duration of which depends on the amplitude of the signal - the shorter the rise time, the longer the flash duration . If the flashes are detected, the output will be a demodulated signal proportional to the average value of the flash envelope.

The gain of the transistor itself can be small (units, tens), sufficient only for self-excitation of oscillations, while the gain of the entire superregenerator, equal to the ratio of the amplitude of the demodulated output signal to the amplitude of the input signal, is very large. The described operating mode of the superregenerator is called nonlinear, or logarithmic, since the output signal is proportional to the logarithm of the input signal.

This introduces some nonlinear distortions, but also plays a useful role - the sensitivity of the super-regenerator to weak signals is greater, and less to strong signals - a natural AGC operates here. To complete the description, it must be said that a linear mode of operation of the superregenerator is also possible if the duration of the power pulse (see Fig. 2) is less than the rise time of the oscillations.

The latter will not have time to increase to the maximum amplitude, and the transistor will not enter the limiting mode. Then the amplitude of the flash will become directly proportional to the amplitude of the signal. This mode, however, is unstable - the slightest change in the transistor gain or the equivalent circuit resistance r will lead to either a sharp drop in the amplitude of the flashes, and therefore the gain of the super-regenerator, or the device will enter a nonlinear mode. For this reason, the linear mode of the superregenerator is rarely used.

It should also be noted that it is absolutely not necessary to switch the supply voltage in order to obtain flashes of oscillations. With equal success, you can apply an auxiliary superization voltage to the lamp grid, base or gate of a transistor, modulating their gain, and therefore feedback. The rectangular shape of the damping oscillations is also not optimal; a sinusoidal shape is preferable, or even better, a sawtooth shape with a gentle rise and a sharp decline. In the latter version, the super-regenerator smoothly approaches the point at which oscillations occur, the bandwidth narrows somewhat, and amplification appears due to regeneration. The resulting fluctuations grow slowly at first, then faster and faster.

The decline in oscillations is as fast as possible. The most widespread are superregenerators with autosuperization, or self-quenching, which do not have a separate auxiliary oscillation generator. They only work in nonlinear mode. Self-quenching, in other words, intermittent generation, can be easily obtained in a device made according to the circuit in Fig. 1, it is only necessary that the time constant of the R1C2 chain be greater than the rise time of the oscillations.

Then the following will happen: the resulting oscillations will cause an increase in the current through the transistor, but the oscillations will be supported for some time by the charge of capacitor C2. When it is used up, the voltage at the emitter will drop, the transistor will close and the oscillations will stop. Capacitor C2 will begin to charge relatively slowly from the power source through resistor R1 until the transistor opens and a new flash occurs.

Stress diagrams in a superregenerator

Voltage oscillograms at the transistor emitter and in the circuit are shown in Fig. 4 as they would normally be seen on the screen of a wideband oscilloscope. Voltage levels of 0.5 and 0.4 V are shown completely arbitrarily - they depend on the type of transistor used and its mode.

Rice. 4 Flashes of oscillation.

What happens when an external signal enters the circuit, since the duration of the flash is now determined by the charge of capacitor C2 and, therefore, is constant? As the signal grows, as before, the rise time of the oscillations decreases, and flashes occur more frequently. If they are detected by a separate detector, the average signal level will increase in proportion to the logarithm of the input signal. But the role of a detector is successfully performed by the transistor VT1 itself (see Fig. 1) - the average voltage level at the emitter drops with increasing signal.

Finally, what happens in the absence of a signal? Everything is the same, only the increase in the oscillation amplitude of each flash will begin from a random noise voltage in the super-regenerator circuit. The frequency of outbreaks is minimal, but unstable - the repetition period changes chaotically.

In this case, the gain of the super-regenerator is maximum, and a lot of noise is heard in the phones or loudspeaker. It decreases sharply when tuning to the signal frequency. Thus, the sensitivity of the superregenerator by the very principle of its operation is very high - it is determined by the level of internal noise. Additional information on the theory of super-regenerative technique is given in.

VHF FM receiver with low voltage supply 1.2 V

Now let's look at practical superregenerator circuits. You can find quite a lot of them in the literature, especially from ancient times. An interesting example: a description of a superregenerator, made on just one transistor, was published in the magazine "Popular Electronics" No. 3 for 1968, its brief translation is given in.

The relatively high supply voltage (9 V) provides a large amplitude of oscillation bursts in the super-regenerator circuit, and therefore a large gain. This solution also has a significant drawback: the superregenerator emits strongly, since the antenna is connected directly to the circuit by a coupling coil. It is recommended to turn on such a receiver only somewhere in nature, far from populated areas.

The diagram of a simple VHF FM receiver with low-voltage power supply, developed by the author based on the basic circuit (see Fig. 1), is shown in Fig. 5. The antenna in the receiver is the loop coil L1 itself, made in the form of a single-turn frame made of thick copper wire (PEL 1.5 and higher). Frame diameter 90 mm. The circuit is adjusted to the signal frequency using a variable capacitor (VCA) C1. Due to the fact that it is difficult to tap from the frame, transistor VT1 is connected according to a capacitive three-point circuit - the OS voltage is supplied to the emitter from the capacitive divider C2C3. The superization frequency is determined by the total resistance of resistors R1-R3 and the capacitance of capacitor C4.

If it is reduced to several hundred picofarads, the intermittent generation stops and the device becomes a regenerative receiver. If desired, you can install a switch, and capacitor C4 can be made up of two, for example, with a capacity of 470 pF with 0.047 uF connected in parallel.

Then the receiver, depending on the reception conditions, can be used in both modes. Regenerative mode provides cleaner and better reception, with less noise, but requires significantly higher field strength. The feedback is regulated by a variable resistor R2, the handle of which (as well as the tuning knob) is recommended to be placed on the front panel of the receiver housing.

The radiation of this receiver in super-regenerative mode is weakened for the following reasons: the amplitude of the oscillation flashes in the circuit is small, on the order of a tenth of a volt, and besides, the small loop antenna radiates extremely inefficiently, having a low efficiency in transmission mode. The receiver's AF amplifier is two-stage, assembled according to a direct coupling circuit using transistors VT2 and VT3 of different structures. The collector circuit of the output transistor includes low-impedance headphones (or one telephone) of types TM-2, TM-4, TM-6 or TK-67-NT with a resistance of 50-200 Ohms. Phones from the player will do.

Rice. 5 Schematic diagram of a superregenerator.

The required bias to the base of the first ultrasonic transistor is supplied not from the power source, but through resistor R4 from the emitter circuit of transistor VT1, where, as mentioned, there is a stable voltage of about 0.5 V. Capacitor C5 transmits oscillations of the ultrasonic frequency to the base of transistor VT2.

The ripples of the damping frequency of 30...60 kHz at the input of the ultrasonic amplifier are not filtered, so the amplifier operates as if in a pulse mode - the output transistor closes completely and opens until saturation. The ultrasonic frequency of flashes is not reproduced by phones, but the pulse sequence contains a component with audio frequencies that are audible. Diode VD1 serves to close the extra current of the phones at the moment the pulse ends and the transistor VT3 closes; it cuts off voltage surges, improving the quality and slightly increasing the volume of sound playback. The receiver is powered by a galvanic cell with a voltage of 1.5 V or a disk battery with a voltage of 1.2 V.

The current consumption does not exceed 3 mA; if necessary, it can be set by selecting resistor R4. Setting up the receiver begins by checking the presence of generation by rotating the knob of the variable resistor R2. It is detected by the appearance of quite strong noise in phones, or by observing a “saw” in the form of voltage on capacitor C4 on the oscilloscope screen. The superization frequency is selected by changing its capacitance; it also depends on the position of the variable resistor R2. Avoid keeping the superization frequency close to the stereo subcarrier frequency of 31.25 kHz or its second harmonic of 62.5 kHz, otherwise beats may be heard that interfere with reception.

Next, you need to set the tuning range of the receiver by changing the dimensions of the loop antenna - increasing the diameter lowers the tuning frequency. You can increase the frequency not only by reducing the diameter of the frame itself, but also by increasing the diameter of the wire from which it is made. A good solution is to use a braided piece of coaxial cable rolled into a ring. The inductance also decreases when making a frame from copper tape or from two or three parallel wires with a diameter of 1.5-2 mm. The tuning range is quite wide, and its installation operation can be easily performed without instruments, focusing on the stations being listened to.

In the VHF-2 (upper) range, the KT361 transistor sometimes works unstable - then it is replaced with a higher frequency one, for example, KT363. The disadvantage of the receiver is the noticeable influence of hands brought to the antenna on the tuning frequency. However, it is also typical for other receivers in which the antenna is connected directly to the oscillating circuit. This drawback is eliminated by using an RF amplifier, which “isolates” the super-regenerator circuit from the antenna.

Another useful purpose of such an amplifier is to eliminate the emission of oscillation flashes by the antenna, which almost completely eliminates interference to neighboring receivers. The gain of the URF should be very small, because both the gain and sensitivity of the super-regenerator are quite high. These requirements are best met by a transistor amplifier based on a circuit with a common base or with a common gate. Turning again to foreign developments, let us mention a super-regenerator circuit with a field-effect transistor-based amplifier.

Economical super regenerative receiver

In order to achieve maximum efficiency, the author developed a super-regenerative radio receiver (Fig. 6), consuming a current of less than 0.5 mA from a 3 V battery, and if the RF frequency control is abandoned, the current drops to 0.16 mA. At the same time, the sensitivity is about 1 µV. The signal from the antenna is supplied to the emitter of the transistor URCH VT1, connected according to a circuit with a common base. Since its input impedance is small, and taking into account the resistance of resistor R1, we obtain an input impedance of the receiver of about 75 Ohms, which allows the use of external antennas with a reduction from a coaxial cable or a VHF ribbon cable with a 300/75 Ohm ferrite transformer.

Such a need may arise when the distance from radio stations is more than 100 km. Capacitor C1 of small capacity serves as an elementary high-pass filter, weakening HF interference. Under the best reception conditions, any surrogate wire antenna is suitable. The URCH transistor operates at a collector voltage equal to the base voltage - about 0.5 V. This stabilizes the mode and eliminates the need for adjustment. The collector circuit includes a communication coil L1, wound on the same frame with a loop coil L2. The coils contain 3 turns of PELSHO 0.25 and 5.75 turns of PEL 0.6 wire, respectively. The frame diameter is 5.5 mm, the distance between the coils is 2 mm. The tap to the common wire is made from the 2nd turn of coil L2, counting from the terminal connected to the base of transistor VT2.

To facilitate setup, it is useful to equip the frame with a trimmer with an M4 thread made of magnetodielectric or brass. Another option that makes tuning easier is to replace capacitor C3 with a tuning one, changing the capacitance from 6 to 25 or from 8 to 30 pF. Tuning capacitor C4 type KPV, it contains one rotor and two stator plates. The super-regenerative cascade is assembled according to the already described circuit (see Fig. 1) on transistor VT2.

The operating mode is selected using trimming resistor R4; the frequency of flashes (superization) depends on the capacity of capacitor C5. At the output of the cascade, a two-stage low-pass filter R6C6R7C7 is switched on, which attenuates oscillations with the superization frequency at the input of the ultrasonic filter so that the latter is not overloaded with them.

Rice. 6 Super regenerative cascade.

The used super-regenerative cascade produces a small detected voltage and, as practice has shown, requires two voltage amplification cascades 34. In the same receiver, ultrasonic frequency transistors operate in microcurrent mode (note the high resistance of the load resistors), their amplification is less, so three voltage amplification cascades are used (transistors VT3-VT5) with direct connection between them.

The cascades are covered by OOS through resistors R12, R13, which stabilizes their mode. For alternating current, the OOS is weakened by capacitor C9. Resistor R14 allows you to adjust the gain of the cascades within certain limits. The output stage is assembled according to a push-pull emitter follower circuit using complementary germanium transistors VT6, VT7.

They operate without bias, but there is no step distortion, firstly, due to the low threshold voltage of germanium semiconductors (0.15 V instead of 0.5 V for silicon), and secondly, because that oscillations with the superization frequency still penetrate a little through the low-pass filter into the ultrasonic frequency filter and, as it were, “blur out” the step, acting similar to high-frequency bias in tape recorders.

Achieving high receiver efficiency requires the use of high-impedance headphones with a resistance of at least 1 kOhm. If the goal of achieving maximum efficiency is not set, it is advisable to use a more powerful final ultrasonic frequency device. Setting up the receiver begins with the ultrasonic sounder. By selecting resistor R13, the voltage at the bases of transistors VT6, VT7 is set equal to half the supply voltage (1.5 V).

Make sure that there is no self-excitation at any position of the resistor R14 (preferably using an oscilloscope). It is useful to apply some kind of sound signal with an amplitude of no more than a few millivolts to the ultrasonic sound input and make sure that there is no distortion and the limitation is symmetrical when overloaded. By connecting a super-regenerative cascade, adjusting resistor R4 causes noise to appear in the phones (the amplitude of the noise voltage at the output is about 0.3 V).

It is useful to say that, in addition to those indicated in the diagram, any other silicon high-frequency transistors of the pnp structure work well in the RF frequency control and super-regenerative cascade. Now you can try to receive radio stations by connecting the antenna to the circuit through a coupling capacitor with a capacity of no more than 1 pF or using a coupling coil.

Next, connect the URF and adjust the range of received frequencies by changing the inductance of the coil L2 and the capacitance of the capacitor C3. In conclusion, it should be noted that such a receiver, due to its high efficiency and sensitivity, can be used in intercom systems and in security alarm devices.

Unfortunately, FM reception on a superregenerator is not obtained in the most optimal way: working at the slope of the resonance curve already guarantees a deterioration in the signal-to-noise ratio by 6 dB. The nonlinear mode of the super-regenerator is also not very conducive to high-quality reception, however, the sound quality is quite good.

LITERATURE:

1. Belkin M.K. Super-regenerative radio reception. - Kyiv: Technology, 1968.
2. Hevrolin V. Super-regenerative reception. - Radio, 1953, No. 8, p. 37.
3. VHF FM receiver on one transistor. - Radio, 1970, No. 6, p. 59.
4. "The Last of the Mohicans..." - Radio, 1997, No. 4,0.20,21

This circuit runs on just one 1.5 V battery. An ordinary earphone with a total impedance of 64 Ohms is used as an audio playback device. The battery power passes through the headphone jack, so you just need to pull the headphones out of the jack to turn off the receiver. The sensitivity of the receiver is sufficient that several high-quality HF and DV stations can be used on a 2-meter wire antenna.

Coil L1 is made on a ferrite core 100 mm long. The winding consists of 220 turns of PELSHO 0.15-0.2 wire. Winding is carried out in bulk on a paper sleeve 40 mm long. The tap must be made from 50 turns from the grounded end.

Receiver circuit with just one field-effect transistor

This version of the circuit of a simple single-transistor FM receiver works on the principle of a super-regenerator.

The input coil consists of seven turns of copper wire with a cross-section of 0.2 mm, wound on a 5 mm mandrel with a tap from the 2nd, and the second inductance contains 30 turns of 0.2 mm wire. The antenna is a standard telescopic one, powered by one Krona type battery, the current consumption is only 5 mA, so it will last for a long time. Tuning to a radio station is carried out by a variable capacitor. The sound at the output of the circuit is weak, so almost any homemade ULF will be suitable to amplify the signal.

The main advantage of this scheme in comparison with other types of receivers is the absence of any generators and therefore there is no high-frequency radiation in the receiving antenna.

The radio wave signal is received by the receiver antenna and is isolated by a resonant circuit on inductance L1 and capacitance C2 and then goes to the detector diode and is amplified.

FM receiver circuit using a transistor and LM386.

I present to your attention a selection of simple FM receiver circuits for the range 87.5 to 108 MHz. These circuits are quite simple to repeat, even for beginner radio amateurs, they are not large in size and can easily fit in your pocket.

Despite their simplicity, the circuits have high selectivity and a good signal-to-noise ratio and are quite enough for comfortable listening to radio stations

The basis of all these amateur radio circuits are specialized microcircuits such as: TDA7000, TDA7001, 174XA42 and others.

The receiver is designed to receive telegraph and telephone signals from amateur radio stations operating in the 40-meter range. The path is built according to a superheterodyne circuit with one frequency conversion. The receiver circuit is designed in such a way that a widely available element base is used, mainly transistors of the KT3102 type and 1N4148 diodes.

The input signal from the antenna system is fed to the input bandpass filter on two circuits T2-C13-C14 and TZ-C17-C15. The connection between the circuits is capacitor C16. This filter selects the signal within the range of 7 ... 7.1 MHz. If you want to work in a different range, you can adjust the circuit accordingly by replacing transformer coils and capacitors.

From the secondary winding of the HF transformer TZ, the primary winding of which is the second filter element, the signal goes to the amplifier stage on transistor VT4. The frequency converter is made using diodes VD4-VD7 in a ring circuit. The input signal is supplied to the primary winding of transformer T4, and the smooth range generator signal is supplied to the primary winding of transformer T6. The smooth range generator (VFO) is made using transistors VT1-VT3. The generator itself is assembled on transistor VT1. The generation frequency lies in the range of 2.085-2.185 MHz, this range is set by a loop system consisting of inductance L1, and a branched capacitive component of C8, C7, C6, C5, SZ, VD3.

Adjustment within the above limits is carried out by variable resistor R2, which is the tuning element. It regulates the constant voltage on the VD3 varicap, which is part of the circuit. The tuning voltage is stabilized using a zener diode VD1 and a diode VD2. During the installation process, overlap in the above frequency range is established by adjusting the capacitors SZ and Sb. If you want to work in a different range or with a different intermediate frequency, a corresponding restructuring of the GPA circuit is required. It’s not difficult to do this armed with a digital frequency meter.

The circuit is connected between the base and emitter (common minus) of transistor VT1. The PIC required to excite the generator is taken from a capacitive transformer between the base and emitter of the transistor, consisting of capacitors C9 and SY. RF is released at the emitter VT1 and goes to the amplifier-buffer stage on transistors VT2 and VT3.

The load is on the RF transformer T1. From its secondary winding, the GPA signal is supplied to the frequency converter. The intermediate frequency path is made using transistors VT5-VT7. The output impedance of the converter is low, so the first stage of the amplifier is made using a VT5 transistor according to a common-base circuit. From its collector, the amplified IF voltage is supplied to a three-section quartz filter at a frequency of 4.915 MHz. If there are no resonators for this frequency, you can use others, for example, at 4.43 MHz (from video equipment), but this will require changing the settings of the VFO and the quartz filter itself. The quartz filter here is unusual; it differs in that its bandwidth can be adjusted.

Receiver circuit. The adjustment is carried out by changing the containers connected between the filter sections and the common minus. For this, varicaps VD8 and VD9 are used. Their capacitances are regulated using a variable resistor R19, which changes the reverse DC voltage across them. The filter output is to the T7 RF transformer, and from it to the second stage of the amplifier, also with a common base. The demodulator is made on T9 and diodes VD10 and VD11. The reference frequency signal comes to it from the generator at VT8. It should have a quartz resonator the same as in a quartz filter. The low-frequency amplifier is made using VT9-VT11 transistors. The circuit is two-stage with a push-pull output stage. Resistor R33 regulates the volume.

The load can be both the speaker and headphones. Coils and transformers are wound on ferrite rings. For T1-T7, rings with an outer diameter of 10 mm are used (imported type T37 is possible). T1 - 1-2=16 vit., 3-4=8 vit., T2 - 1-2=3 vit., 3-4=30 vit., TZ - 1-2=30 vit., 3-4= 7 vit., T7 -1-2=15 vit., 3-4=3 vit. T4, TB, T9 - 10 turns of wire folded in three, solder the ends according to the numbers on the diagram. T5, T8 - 10 turns of wire folded in half, solder the ends according to the numbers on the diagram. L1, L2 - on rings with a diameter of 13 mm (imported type T50 is possible), - 44 turns. For all, you can use PEV wire 0.15-0.25 L3 and L4 - ready-made chokes 39 and 4.7 μH, respectively. KT3102E transistors can be replaced with other KT3102 or KT315. Transistor KT3107 - on KT361, but it is necessary that VT10 and VT11 have the same letter indices. 1N4148 diodes can be replaced with KD503. The installation was carried out in a three-dimensional manner on a piece of foil fiberglass laminate measuring 220x90 mm.

This article provides a description of three simple receivers with a fixed tuning to one of the local stations in the MF or LW range; these are extremely simplified receivers powered by a Krona battery, located in subscriber speaker housings containing a speaker and a transformer.

The schematic diagram of the receiver is shown in Figure 1A. Its input circuit is formed by coil L1, capacitor cl and an antenna connected to them. The circuit is tuned to a station by changing capacitance C1 or inductance Ll. The RF signal voltage from part of the coil turns is supplied to the diode VD1, which works as a detector. From variable resistor 81, which is the load of the detector and the volume control, low frequency voltage is supplied to the base VT1 for amplification. The negative bias voltage at the base of this transistor is created by the constant component of the detected signal. Transistor VT2 of the second stage of the low-frequency amplifier has a direct connection with the first stage.

The low-frequency oscillations amplified by it pass through the output transformer T1 to loudspeaker B1 and are converted into acoustic oscillations. The receiver circuit of the second option is shown in the figure. The receiver assembled according to this circuit differs from the first option only in that its low-frequency amplifier uses transistors of different conductivity types. Figure 1B shows a diagram of the third version of the receiver. Its distinctive feature is positive feedback carried out using the L2 coil, which significantly increases the sensitivity and selectivity of the receiver.

To power any receiver, a battery with a voltage of -9V is used, for example, “Krona” or made up of two 3336JI batteries or individual elements; it is important that there is enough space in the subscriber speaker housing in which the receiver is assembled. While there is no signal at the input, both transistors are almost closed and the current consumption of the receiver in rest mode does not exceed 0.2 Ma. The maximum current at the highest volume is 8-12 Ma. The antenna is any wire about five meters long, and the grounding is a pin driven into the ground. When choosing a receiver circuit, you need to take into account local conditions.

At a distance of about 100 km from the radio station, using the above antenna and grounding, loud-speaking reception by receivers is possible according to the first two options; up to 200 km - the scheme of the third option. If the distance to the station is no more than 30 km, you can get by with an antenna in the form of a wire 2 meters long and without grounding. The receivers are mounted by volumetric installation in the housings of subscriber loudspeakers. Remaking the loudspeaker comes down to installing a new volume control resistor combined with the power switch and installing sockets for the antenna and grounding, while the isolation transformer is used as T1.

Receiver circuit. The input circuit coil is wound on a piece of ferite rod with a diameter of 6 mm and a length of 80 mm. The coil is wound on a cardboard frame so that it can move along the rod with some friction. To receive DV radio stations, the coil must contain 350, with a tap from the middle, turns of PEV-2-0.12 wire. To operate in the CB range there must be 120 turns with a tap from the middle of the same wire; the feedback coil for the receiver of the third option is wound on a contour coil, it contains 8-15 turns. Transistors must be selected with a gain Vst of at least 50.

Transistors can be any germanium low-frequency of the appropriate structure. The transistor of the first stage must have the minimum possible reverse collector current. The role of a detector can be performed by any diode of the D18, D20, GD507 and other high-frequency series. The variable volume control resistor can be of any type, with a switch, with a resistance from 50 to 200 kilo-ohms. It is also possible to use a standard resistor of the subscriber loudspeaker; usually resistors with a resistance of 68 to 100 kohms are used. In this case, you will have to provide a separate power switch. A trimmer ceramic capacitor KPK-2 was used as a loop capacitor.

Receiver circuit. It is possible to use a variable capacitor with a solid or air dielectric. In this case, you can insert a tuning knob into the receiver, and if the capacitor has a sufficiently large overlap (in a two-section, you can connect two sections in parallel, the maximum capacity will double) you can receive stations in the LW and SW range with one medium-wave coil. Before tuning, you need to measure the current consumption from the power source with the antenna disconnected, and if it is more than one milliampere, replace the first transistor with a transistor with a lower reverse collector current. Then you need to connect the antenna and by rotating the rotor of the loop capacitor and moving the coil along the rod, tune the receiver to one of the powerful stations.

Converter for receiving signals in the 50 MHz range The IF-LF transceiver path is intended for use in the latter, superheterodyne circuit, with single frequency conversion. The intermediate frequency is chosen to be 4.43 MHz (quartz from video equipment is used)

Magnetic ferrite antennas are good for their small size and well-defined directivity. The antenna rod should be positioned horizontally and perpendicular to the direction of the radio. In other words, the antenna does not receive signals from the ends of the rod. In addition, they are insensitive to electrical interference, which is especially valuable in large cities, where the level of such interference is high.

The main elements of a magnetic antenna, designated in the diagrams by the letters MA or WA, are an inductor coil wound on a frame made of insulating material, and a core made of high-frequency ferromagnetic material (ferrite) with high magnetic permeability.

Receiver circuit. Non-standard detector

Its circuit differs from the classical one, first of all, in a detector built on two diodes and a coupling capacitor, which allows you to select the optimal circuit load for the detector, and thereby obtain maximum sensitivity. With a further decrease in capacitance C3, the resonance curve of the circuit becomes even sharper, i.e., the selectivity increases, but the sensitivity decreases somewhat. The oscillating circuit itself consists of a coil and a variable capacitor. The inductance of the coil can also be varied within wide limits by moving the ferrite rod in and out.

Prologue.

I have two multimeters, and both have the same drawback - they are powered by a 9-volt Krona battery.

I always tried to have a fresh 9-volt battery in stock, but for some reason, when it was necessary to measure something with an accuracy higher than that of a pointer instrument, the Krona turned out to be either inoperative or only lasted for a few hours of operation.

The procedure for winding a pulse transformer.

It is very difficult to wind a gasket onto a ring core of such small dimensions, and winding a wire onto a bare core is inconvenient and dangerous. The wire insulation may be damaged by the sharp edges of the ring. To prevent damage to the insulation, dull the sharp edges of the magnetic circuit as described.

To prevent the turns from running apart when laying the wire, it is useful to cover the core with a thin layer of “88N” glue and dry it before winding.

First, the secondary windings III and IV are wound (see converter diagram). They need to be wound into two wires at once. The coils can be secured with glue, for example, “BF-2” or “BF-4”.

I did not have a suitable wire, and instead of a wire with a calculated diameter of 0.16 mm, I used a wire with a diameter of 0.18 mm, which led to the formation of a second layer of several turns.

Then, also in two wires, primary windings I and II are wound. The turns of the primary windings can also be secured with glue.

I assembled the converter using the hinged mounting method, having previously connected the transistors, capacitors and transformer with cotton thread.

The input, output and common bus of the converter were connected with a flexible stranded wire.

Setting up the converter.

Tuning may be required to set the desired output voltage level.

I selected the number of turns so that at a battery voltage of 1.0 Volts, the output of the converter would be about 7 Volts. At this voltage, the low battery indicator lights up in the multimeter. This way you can prevent the battery from being discharged too deeply.

If instead of the proposed KT209K transistors, others are used, then the number of turns of the secondary winding of the transformer will have to be selected. This is due to the different magnitude of the voltage drop across p-n junctions for different types of transistors.

I tested this circuit using KT502 transistors with unchanged transformer parameters. The output voltage dropped by a volt or so.

You also need to keep in mind that the base-emitter junctions of transistors are also output voltage rectifiers. Therefore, when choosing transistors, you need to pay attention to this parameter. That is, the maximum permissible base-emitter voltage must exceed the required output voltage of the converter.

If generation does not occur, check the phasing of all coils. The dots on the converter diagram (see above) mark the beginning of each winding.

To avoid confusion when phasing the coils of the ring magnetic circuit, take as the beginning of all windings, For example, all leads coming out from the bottom, and beyond the end of all windings, all leads coming out from the top.

Final assembly of a pulse voltage converter.

Before final assembly, all elements of the circuit were connected with stranded wire, and the circuit's ability to receive and transmit energy was tested.

To prevent short circuits, the pulse voltage converter was insulated on the contact side with silicone sealant.

Then all the structural elements were placed in the Krona body. To prevent the front cover with the connector from being recessed inside, a celluloid plate was inserted between the front and back walls. After which, the back cover was secured with “88N” glue.

To charge the modernized Krona, we had to make an additional cable with a 3.5mm jack plug at one end. At the other end of the cable, to reduce the likelihood of a short circuit, standard device sockets were installed instead of similar plugs.

Refinement of the multimeter.

The DT-830B multimeter immediately started working with the upgraded Krona. But the M890C+ tester had to be slightly modified.

The fact is that most modern multimeters have an automatic power-off function. The picture shows part of the multimeter control panel where this function is indicated.

The Auto Power Off circuit works as follows. When the battery is connected, capacitor C10 is charged. When the power is turned on, while capacitor C10 is discharged through resistor R36, the output of comparator IC1 is held at a high potential, which causes transistors VT2 and VT3 to turn on. Through the open transistor VT3, the supply voltage enters the multimeter circuit.

As you can see, for normal operation of the circuit, you need to supply power to C10 even before the main load turns on, which is impossible, since our modernized “Krona”, on the contrary, will turn on only when the load appears.

In general, the whole modification consisted of installing an additional jumper. For her, I chose the place where it was most convenient to do this.

Unfortunately, the designations of the elements on the electrical diagram did not match the designations on the printed circuit board of my multimeter, so I found the points for installing the jumper this way. By dialing, I identified the required output of the switch, and identified the +9V power bus using the 8th leg of the operational amplifier IC1 (L358).

Small details.

It was difficult to purchase just one battery. They are mostly sold either in pairs or in groups of four. However, some kits, for example, “Varta”, come with five batteries in a blister. If you are as lucky as I am, you will be able to share such a set with someone. I bought the battery for only $3.3, while one “Krona” costs from $1 to $3.75. There are, however, also “Crowns” for $0.5, but they are completely stillborn.

A diagram of a medium-wave regenerative receiver from V. T. Polyakov caught my eye. In order to test the operation of regenerators in the medium wave range, this receiver was manufactured.

The original circuit of this regenerative radio receiver designed to operate in the medium wave range looks like this:

A regenerative cascade is assembled on transistor VT1; the regeneration level is regulated by resistor R2. The detector is assembled using transistors VT2 and VT3. A ULF is assembled using transistors VT4 and VT5, designed to work with high-impedance headphones.

Reception is carried out using a magnetic antenna. The station is tuned using a variable capacitor C1. A detailed description of this radio receiver, as well as the procedure for setting it up, are described in the CQ-QRP magazine No. 23.

Description of the medium-wave regenerative radio receiver I made.

As usual, I always make small changes to the original design of the designs I repeat. In this case, to ensure loud-speaking reception, a low-frequency amplifier on the TDA2822M chip is used.

The final circuit of my receiver looks like this:

The magnetic antenna used is ready-made from some kind of radio receiver, on a ferrite rod 200 mm long.

The long-wave coil was removed as unnecessary. The medium-wave contour coil was used without modifications. The communication coil was broken, so I wound a communication coil next to the “cold” end of the loop coil. The communication coil consists of 6 turns of PEL 0.23 wire:

Here it is important to observe the correct phasing of the coils: the end of the loop coil must be connected to the beginning of the communication coil, the end of the communication coil is connected to the common wire.

The low-frequency amplifier consists of a preliminary stage assembled on a VT4 transistor of type KT201. This stage uses a low-frequency transistor to reduce the likelihood of ULF self-excitation. Setting up this cascade comes down to selecting resistor R7 to obtain a voltage on the VT4 collector equal to approximately half the supply voltage.

The final low-frequency amplifier is assembled on a TDA2822M microcircuit, connected according to a standard bridge circuit. The detector is assembled using transistors VT2 and VT3 and does not require adjustment.

In the original version, the receiver was assembled in accordance with the author's diagram. Trial operation revealed insufficient sensitivity of the receiver. In order to increase the sensitivity of the receiver, a radio frequency amplifier (RFA) was additionally mounted on a VT5 transistor. Setting it up comes down to obtaining a voltage on the collector of about three volts by selecting resistor R14.

The regenerative cascade is assembled on a field-effect transistor KP302B. Setting it up comes down to setting the source voltage within 2...3V with resistor R3. After this, be sure to check for the presence of generation when changing the resistance of resistor R2. In my version, generation occurred when the resistor R2 slider was in the middle position. The generation mode can also be selected using resistor R1.

In case of insufficiently loud reception, it will be useful to connect a piece of wire no more than 1 m long to the gate of transistor VT1 through a 10 pF capacitor. This wire will act as an external antenna. The actual DC modes of the transistors in my receiver version are shown in the diagram.

This is what an assembled medium-wave regenerative radio receiver looks like:

The receiver was tested over several evenings at the end of September and beginning of October 2017. There are many medium-wave radio broadcast stations, and many of them are received at deafening volumes. Of course, this receiver also has disadvantages - for example, stations located nearby sometimes overlap each other.

But, in general, this medium-wave regenerative radio receiver performed very well.

A short video demonstrating the operation of this regenerative receiver:

Receiver circuit board. View from the side of the printed conductors. The board is designed for specific parts, in particular KPI.