Low-voltage radio power supply. Simple DIY radio Receiver with 1.5 volt power supply

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 amplifier, 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 achieve 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 oscillatory 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 terminal. 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, may well 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 frequency. 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 widely used 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 maintained 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 passes AF oscillations 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 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 RF gain should be very small, since 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 diameter of the frame 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 by 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 amplifier 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 slider (preferably using an oscilloscope). It is useful to apply some kind of audio 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 that the limitation is symmetrical when overloaded. By connecting a super-regenerative cascade, by adjusting resistor R4, noise appears 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

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 NE 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. See photo.

The radio signal induced by 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 oscillatory 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 ​​the 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 the 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.

Receivers. receivers 2 receivers 3

Heterodyne receiver for 20 m range "Practice"

Rinat Shaikhutdinov, Miass

The receiver coils are wound on standard four-section frames with dimensions of 10x10x20 mm from the coils of portable receivers and are equipped with ferrite trimming cores with a diameter of 2.7 mm from the material

30HF. All three coils are wound with PELSHO (better) or PEL 0.15 mm wire. Coil L1 contains 4 turns, L2 – 12 turns, L3 – 16 turns. The coils are evenly distributed among the sections of the frame. The tap of coil L3 is made from the 6th turn, counting from the terminal connected to the common wire. Coils L1 and L2 are wound as follows: first, coil L1 into the lower section of the frame, then into the three upper sections - 4 turns of loop coil L2 each. The coil data is indicated for a range of 20 meters and a capacitance of loop capacitors C1 and C7 of 100 pF each. If you want to make this receiver for other bands, it is useful to be guided by the following rule: Capacitance of loop capacitors

change inversely proportional to the frequency ratio, and the number of turns of the coils - 28 - is inversely proportional to the square root of the frequency ratio. For example, for a range of 80 meters (frequency ratio 1:4), the capacitor capacity should be

take 400 pF (the nearest nominal value is 390 pF), the number of turns of coils L1...3 is 8, 24 and 32 turns, respectively. Of course, all this data is approximate and needs to be clarified when setting up the assembled receiver. Choke L4 at the ULF output is any factory one, with an inductance of 10 µH and higher. In the absence of one, you can wind 20...30 turns of any

insulated wire to a cylindrical trimmer with a diameter of 2.7 mm from the IF circuits of any receiver (they use ferrite with a permeability of 400 - 1000). The dual KPI is used from VHF units of industrial radio receivers, the same as in the author’s previous designs, already published in the magazine. The remaining parts can be of any type. A sketch of the receiver printed circuit board and the placement of parts are shown in Fig. 2.

When laying out the board, a useful and, in some cases, urgently necessary principle was followed: to leave the maximum area of ​​the common conductor – the “ground” – between the tracks.

QRP PP receiver for 40 meters

Rinat Shaikhutdinov

The receiver showed good results, providing high-quality reception to many amateur stations, so a printed circuit board was developed. The receiver circuit has undergone minor changes: an isolation capacitor is installed at the input of the ultrasonic sounder, made on the common LM386 microcircuit.

This increased the stability of the chip mode and improved the operation of the mixer

The input attenuator successfully serves as a volume control. Coil data

were given in the previous issue, but in order not to search, we will give them again.

The frames of the coils and KPI are taken from VHF units, the coils are adjusted

30HF cores. L1 and L2 are wound on the same frame, contain 4 and 16 turns, respectively, L3 - also 16 turns, local oscillator coil L4 - 19 turns with tapping from the 6th turn. Wire – PEL 0.15. Low-pass filter coil L5 is imported, ready-made, with an inductance of 47 mH. The remaining parts are of the usual types. Transistor 2N5486 can be replaced with KP303E, and transistor KP364 with KP303A

Simple superheterodyne at 40 meters

A receiver from the simplest series, with a minimum number of parts, for a range of 40 meters. AM-SSB-CW modulation is switched by the BFO switch. A piezoelectric filter with a frequency of 455 or 465 kHz is used as a selective element. Inductors are calculated by one of the programs posted on the site or borrowed from other designs.

Receiver “It couldn’t be simpler”

The receiver is built using a superheterodyne circuit with a quartz filter and has a sensitivity sufficient to receive amateur radio stations. The receiver's local oscillator is located in a separate metal box and covers the range of 7.3-17.3 MHz. Depending on the settings of the input circuit, the range of received frequencies is in the range of 3.3-13.3 and 11.3-21.3 MHz. USB or LSB (and at the same time smooth adjustment) are tuned by the local oscillator resistor BFO. When using a quartz filter for other frequencies, the local oscillator should be recalculated.

4-band direct conversion receiver

HF receiver from DC1YB

The HF receiver with upconversion is built according to a triple conversion scheme and covers 300 kHz - 30 MHz. The received frequency range is continuous. Additional fine tuning allows SSB and CW reception. Receiver intermediate frequencies are 50.7 MHz, 10.7 MHz and 455 kHz. The receiver uses cheap filters at 10.7 MHz 15 kHz and industrial 455 kHz. The first VFO covers the frequency band from 51 MHz to 80.7 MHz. using a KPE with an air dielectric, but the author does not exclude the use of a synthesizer.

Receiver circuit

Simple HF receiver

Economical radio receiver

S. Martynov

Nowadays, the efficiency of radio receivers is becoming increasingly important. As you know, many industrial receivers are not very economical, and yet in many populated areas of the country long-term power outages have become commonplace. The cost of batteries also becomes burdensome when replacing them frequently. And far from “civilization,” an economical radio is simply necessary.

The author of this publication set out to create an economical radio receiver with high sensitivity and the ability to operate in the HF and VHF bands. The result was quite satisfactory - the radio receiver is capable of operating from one battery

Main technical characteristics:

Received frequency range, MHz:

• KV-1 ................... 9.5...14;
• KV-2............... 14.0 ... 22.5;
• VHF-1 ............ 65...74;
• VHF-2 ............ 88...108.

Selectivity of the AM path on the adjacent channel, dB,

• not less......................... 30;

Maximum output power at 8 Ohm load, mW, at supply voltage:

The sensitivity of the radio receiver when properly configured...

Radio receiver circuit

Mini-Test-2band

The dual-band receiver is designed for listening to amateur radio stations in CW, SSB and AM modes on the two most popular bands of 3.5 (night) and 14 (day) MHz. The receiver does not contain a very large number of components, non-scarce radio components, and is very easy to set up, which is why it has the word “Mini” in its name. It is a superheterodyne with one frequency conversion. The intermediate frequency is fixed – 5.25 MHz. This IF allows you to receive two frequency sections (main and mirror) without switching elements in the GPA. Changing ranges is done by simply switching radio elements in the input filter. The receiver uses a new, newly developed IF amplifier and improved AGC circuitry. The sensitivity of the receiver is about 3 µV, the dynamic range of blockage is about 90 dB. The receiver is powered by +12 volts.

Mini-Test-many-band

Rubtsov V.P. UN7BV. Kazakhstan. Astana.

The multi-band receiver is designed for listening to amateur radio stations in CW, SSB and AM modes on bands 1.9; 3.5; 7.0; 10, 14, 18, 21, 24, 28 MHz. The receiver does not contain a very large number of components, non-scarce radio components, is very easy to set up, which is why it has the word “Mini” in its name, and the word “many” indicates the ability to receive radio stations on all amateur bands. It is a superheterodyne with one frequency conversion. The intermediate frequency is fixed – 5.25 MHz. The use of this IF is due to the small presence of affected points, the large gain of the IF at this frequency (which somewhat improves the noise parameters of the path), and the overlap of the 3.5 and 14 MHz ranges in the GPA with the same trimming elements. That is, this frequency is a “legacy” from the previous dual-band version of the “Mini-Test” receiver, which turned out to be quite good in the multi-band version of this receiver. The receiver uses a new, recently developed IF amplifier, sensitivity is increased to 1 µV and, in connection with the increase in the latter, the operation of the AGC system is improved, and the function of adjusting the AGC depth is introduced.

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. Its setup 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 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 broadcasting 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.

Homemade radios

When developing this radio receiver, the task was to create a design that was easy to replicate, had a minimum of coil parts, had sufficient sound quality and volume, and had the ability to operate in a wide range of supply voltages.

The result was a design consisting of three modern microcircuits:
KS1066ХА1 (К174ХА2) - the radio receiver itself
BA3822L- equalizer
TDA2030 - bass amplifier
Each path is made in the form of a separate module (printed circuit board drawings are presented below).

The general technical characteristics of the radio receiver are as follows:
1. Sensitivity at a signal/noise ratio of 26 dB...............6 µV/m
2. Range of received frequencies...................VHF 65.8-73 MHz or FM 88-108 MHz
3. Nonlinear distortion coefficient no more than....................2%
4. APCG capture band............................300 kHz
5. Supply voltage range................4.5-25 Volts (nominal 6-20 Volts)
6. Output power into a 4 Ohm load at a supply voltage of 20 V.......... 6 W