Simple TLG filters for shortwave receiver circuits. Scheme of an all-wave HF receiver › Schemes of electronic devices. Low sensitivity tube devices

V. Polyakov (RA3AAE)

Continuing the series of articles on the basics of amateur radio communications, which began in the August issue of the magazine last year with a description of a simple transmitter with quartz stabilization for the amateur band of 160 meters, we propose the design of a simple heterodyne radio receiver for the same range. The receiver may be of interest to both novice shortwave observers and more experienced radio athletes. Thanks to its cost-effectiveness and small dimensions, the receiver is especially suitable for use in the field.

Conventional mass broadcast receivers are unsuitable for receiving signals from amateur radio stations without such significant modernization that it is easier to build the receiver anew. The point is not even their low sensitivity and excessively wide bandwidth, but the fact that they are designed to receive amplitude-modulated (AM) signals. Amateurs have long abandoned AM due to its low efficiency and use exclusively telegraph (CW) or single-sideband (SSB) speech signal on short waves (KB). For this reason, the receiver must be designed on completely different principles. In particular, it does not require an amplitude detector, and it is advisable to do the main amplification at low audio frequencies, where it is much easier and cheaper.

The CW signal consists of short and long bursts of an unmodulated carrier frequency lying in one of the amateur radio bands, in our case 1.8...2 MHz (160 meters). In order for the signal to sound like the usual Morse code melody, its high frequency must be converted down to the 3H range. This is done by a frequency converter installed at the receiver input (Fig. 1), immediately after the input filter Z1, containing a mixer U1 and a low-power auxiliary oscillator - local oscillator G1.

Let's say we want to receive a CW signal at 1900 kHz. By tuning the local oscillator to a frequency of 1901 kHz, we obtain sum (3801 kHz) and difference (1 kHz) frequency signals at the mixer output. We don’t need the total frequency, but we will filter the difference audio frequency signal (Z2), amplify it in ultrasonic sounder A1 and send it to BF1 phones. As you can see, the receiver is really very simple.

An SSB signal is the same audio signal, but with a spectrum shifted to radio frequencies. On low-frequency amateur bands (160, 80 and 40 meters), the spectrum of the SSB signal is also inverted (the lower sideband, LSB, is emitted). This means that with a SSB signal carrier frequency of 1900 kHz, its spectrum extends from 1897 to 1899.7 kHz, i.e. 1900 kHz - (0.3....3 kHz). The suppressed upper side (USB) occupies the frequency band 1900.3...1903 kHz, as can be seen in the spectrogram (Fig. 2). The emitted LSB is highlighted by thick lines. To receive this signal, it is enough to tune the local oscillator exactly to the frequency of 1900 kHz.

The heterodyne receiver was invented at the dawn of radio engineering, approximately in 1903, when there were no lamps or other amplifying devices, but there were already antennas, telephones and continuous oscillation generators (arc, electric machine). For the next decade, exclusively heterodyne receivers were used for auditory reception of telegraph signals. Then the tube regenerator, or audion (1913), the superheterodyne (1917), which, by the way, got its name from the heterodyne receiver, were invented; AM began to be widely used, and heterodyne receivers were firmly and for a long time forgotten.

Radio amateurs revived this technique in the 60-70s of the last century, proving in practice that a receiver with three or four transistors can receive radio stations from all continents, working no worse than large multi-tube devices. But the name became different - receiver direct conversion(Direct Conversion Receiver, DCR), which emphasized the fact of direct conversion (namely conversion, not detection) of the radio signal frequency into a low audio frequency.

Referring again to Fig. 1, let us explain the purpose of filters. The Z1 input bandpass filter attenuates strong out-of-band signals from service and broadcast stations that may cause interference. Its bandwidth can be equal to the width amateur band, and if it is narrower, the filter is made tunable. It also weakens side reception channels that are possible at local oscillator harmonics. The Z2 filter is a low-pass filter that passes only the “telephone” band of audio frequencies below about 3 kHz. The most low frequencies, below 300 Hz, are sufficiently attenuated by separating capacitors in the ultrasonic sounder.

Filter Z2 determines the selectivity of the receiver: signals from radio stations located further than 3 kHz from the local oscillator frequency will create frequencies above 3 kHz at the output of the mixer, and therefore will be effectively filtered in the low-pass filter. Added to the selectivity of the receiver is the selectivity of telephones, which poorly reproduce frequencies above 2.5...3 kHz, and the natural selectivity of human hearing, which perfectly distinguishes the tone of signals and highlights the useful signal against the background of interference - after all, if the frequencies differ in the radio range, after conversion they will vary in the audio range. There is no trace of this in AM receivers with a detector - it doesn’t care what signals to detect (it does not respond to frequency), as a result, all signals passing through the radio path create interference.

The disadvantages of a heterodyne receiver include dual-sideband reception: in our example of CW reception, an interfering signal with a frequency of 1902 kHz will also give a difference frequency of 1 kHz and will be received. Sometimes such interference can be eliminated. The fact is that for a signal with a frequency of 1900 kHz, two settings are possible - upper (the local oscillator frequency is 1901 kHz) and lower (1899 kHz). If interference is audible with one setting, it may not be with another.

On an SSB signal, only one setting is possible - 1900 kHz, but all signals with frequencies of 1900 ... 1903 kHz will create interference (see Fig. 2) and cannot be eliminated. This drawback is significant only during “pile-up” reception, when many stations “huddled together” at close frequencies, hearing, for example, the rare “DX”. During normal reception, when there are few stations and there are significant gaps between their frequencies, this drawback is completely unnoticeable.

The schematic diagram of the receiver is shown in Fig. 3. The input signal from the antenna is fed through a small capacitance coupling capacitor C1 to a double-circuit bandpass filter. The first circuit of the L1C2C3C4.1 filter has a relatively high quality factor and, therefore, a narrow bandwidth, so it is frequency tuned using one section of the dual C4.1 KPI. There is no need to rebuild the second L2C7 circuit, since it is heavily loaded by the mixer, its quality factor is lower, and its bandwidth is wider, so it does not tune and passes the entire frequency band of 1.8...2 MHz.

The receiver mixer is assembled on two diodes VD1 and VD2, connected back-to-back. Through capacitor C8 (it is also included in the low-pass filter), the local oscillator voltage from the tap of coil L3 is supplied to the mixer. The local oscillator is tuned in the frequency band 0.9...1 MHz by another section of the KPI - S4.2. As you can see, the local oscillator frequency is half the signal frequency, which is necessary by the very principle of operation of the mixer. It works as follows. To open silicon diodes, a voltage of about 0.5 V is required, and the amplitude of the heterodyne voltage supplied to the diodes barely reaches 0.55...0.6 V. As a result, the diodes alternately open only at the peaks of the positive and negative half-waves of the heterodyne voltage, i.e. i.e. twice per period.

This is how the signal circuit is switched with double the local oscillator frequency. The mixer is especially convenient for heterodyne receivers, since the local oscillator signal is practically not emitted by the antenna, being greatly attenuated by the input filter, and does not create interference either to others (the first heterodyne receivers sinned with this, in which the local oscillator operated at the signal frequency and it was not easy to suppress its radiation) or to its own reception.

The local oscillator is made according to the “inductive three-point” circuit on transistor VT1. Its circuit L3C6C5C4.2 is included in the collector circuit of the transistor, and the signal feedback enters the emitter circuit through capacitor C9. The required base bias current is set by resistor R1, shunted for high frequency currents by capacitor C10.

The converter is designed in such a way that it does not require painstaking work to select the optimal local oscillator voltage on the mixer diodes. This is facilitated by the easy operating mode of the local oscillator at a low collector-emitter voltage of the transistor (about 1.5 V) and a low collector current - less than 0.1 mA (note the high resistance of resistor R2). Under these conditions, the local oscillator is excited easily, but as soon as the oscillation amplitude increases to approximately 0.55 V at the coil tap, the mixer diodes open at the peaks of the oscillations and bypass the local oscillator circuit, limiting further growth in amplitude.

The low-pass filter of the C8L4C11 receiver is the simplest U-shaped filter of the third order, providing a slope of 18 dB per octave (double the frequency) above the cutoff frequency of 3 kHz.

The receiver's ultrasonic frequency is two-stage, it is assembled on low-noise transistors VT2 and VT3 of the KT3102 series with a high current transfer coefficient. To simplify the amplifier, direct communication between the stages is used. The resistor resistances are selected so that the transistor mode is DC is set automatically and depends little on temperature fluctuations and supply voltage. The current of transistor VT3, passing through resistor R5, connected to the emitter circuit, causes a voltage drop across it of about 0.5 V, sufficient to open transistor VT2, the base of which is connected through resistor R4 to the emitter VT3. As a result, when opening, transistor VT2 lowers the voltage at the base of VT3, preventing a further increase in its current.

In other words, the ultrasonic sounder is covered by 100% negative feedback (NFE) for direct current, which strictly stabilizes its mode. This is facilitated by the relatively large (compared to generally accepted) resistance of the collector load VT1 - resistor R3 and the small one - resistor R4. On alternating current of audio frequencies, the OOS does not work, since they are closed through a large-capacity blocking capacitor C15. A variable resistor R6 is connected in series with it - the volume control. By introducing some resistance, we thereby create some OOS, which reduces the gain. This method of volume control is good because the regulator is already installed in the circuit amplified signal and does not require shielding. In addition, the introduced OOS reduces the already small signal distortion in the amplifier. The disadvantage is that the volume is not adjusted to zero, but usually this is not necessary. The phones are connected to the collector circuit of the VT3 transistor (via connector XS3), and both the alternating signal current and the direct current of the transistor flow through their coils, which additionally magnetizes the phones and improves their operation. It does not require setting up an ultrasonic sounder.

About the details. Start selecting them with headphones. We need ordinary telephones of the electromagnetic system with tin membranes, necessarily high-resistance, with a total direct current resistance of 3.2...4.4 kOhm (from telephone sets are not suitable - they are low-resistance). The author used TA-56m phones with a resistance of each 1600 Ohms (indicated on the case). TA-4, TON-2, TON-2m, still produced by the Oktava plant, are also suitable. Miniature headphones from players with low sensitivity cannot be used with this receiver.

The phone power plug is replaced with a standard round three- or five-pin connector from sound-reproducing equipment. A jumper is installed between pins 2 and 3 of the pin part of the connector, which is used to connect the power battery GB1. When the phones are disconnected, the battery will turn off automatically. The former positive terminal of the telephone cord is connected to pin 2, this will ensure the addition of magnetic fluxes created by the bias current and the permanent magnets of the telephones.

The next important detail is the KPI. The author was lucky - he managed to find a small-sized dual KPI from a portable transistor receiver with a built-in ball vernier. It is possible to use a KPI without a vernier; receiving CW stations will not cause problems, but precise tuning on an SSB station will be difficult, since the tuning density of 400 kHz per revolution is too high. Select the maximum diameter adjustment knob or construct your own vernier using a suitable pulley and cable. KPI with an air dielectric is better, but small-sized KPI with a solid dielectric from transistor receivers are also suitable. Often they are already equipped with vernier pulleys. The capacitance of the capacitor is not critical; the required range overlap can be selected using “stretching” capacitors SZ, C5 (their capacitances must be the same) and C2, C6 (the capacitances are also the same).

The receiver coils are wound on standard three-section frames used in transistor receivers. If frames have four sections, the section closest to the base is not used. The turns are evenly distributed in all three sections of the frame, winding is carried out in bulk. The frames are equipped with ferrite cores with a diameter of 2.7 mm. A PEL wire with a diameter of 0.12-0.15 mm is suitable, but it is advisable to use PELSHO, or even better - Litz wire twisted from several (5-7) PEL conductors 0.07-0.1 or ready-made Litz wire in a silk braid, for example, LESHO 7x0.07.

Coils L1 and L2 contain 70 turns each, L3 - 140 turns with a tap from the 40th turn, counting from the terminal connected to the common wire. The low-pass filter coil L4 is wound on a ring K10x7x4 made of ferrite with a magnetic permeability of 2000 and contains 240 turns of PEL or PELSHO wire 0.07-0.1. Winding it in the absence of experience can result in a problem (the author wound it in less than an hour). Use a shuttle soldered from two pieces copper wire about 10 cm long. At the ends, the wires are slightly separated, forming “forks” into which a thin winding wire is placed. It is better to fold it in half and wind 120 turns, then connect the beginning of one wire to the end of the other (an ohmmeter is needed to identify the terminals). The resulting middle output is not used.

Coil L4 can be replaced primary winding output or transition transformer from pocket receivers. If its inductance turns out to be too large and the low-pass filter cutoff frequency decreases, which will be noticeable by ear attenuation higher frequencies sound spectrum, the capacitance of capacitors C8 and C11 should be slightly reduced. In extreme cases, the coil can even be replaced with a resistor with a resistance of 2.7...3.6 kOhm. In this case, the capacitance of capacitors C8 and C11 must be reduced by 2...3 times, the selectivity and sensitivity of the receiver will decrease somewhat.

The capacitors included in the circuits must be ceramic, mica or film, with good capacitance stability. Miniature capacitors with non-standardized TKE (temperature coefficient of capacitance) are not suitable here; they are usually orange. Don’t be afraid to use vintage capacitors of the KT, KD (ceramic tubular or disk) or KSO (pressed mica) types. The requirements for capacitors C8-C11 are less stringent; any ceramic or metal-paper (MBM) are suitable here, except for capacitors made of low-frequency ceramics of the TKE H70 and H90 groups (the capacity of the latter can change almost 3 times with temperature fluctuations). There are no special requirements for other capacitors and resistors. The capacitance of capacitor C12 can range from 0.1 to 1 µF, C13 - from 50 µF and above, C15 - from 20 to 100 µF. Variable volume control resistor - any small-sized one, for example, type SPZ-4.

It is permissible to use almost any silicon high-frequency diodes in the mixer, for example, the KD503, KD512, KD520-KD522 series. In addition to the KT361B (VT1) transistor indicated in the diagram, any of the KT361, KT3107 series will be suitable. Transistors VT2, VT3 - any silicon with a current transfer coefficient of 150...200 or more.

The flat six-volt battery was taken from a used Polaroid camera cassette. Other options are also possible: four galvanic cells in series connection, a Krona battery. The current consumed by the receiver does not exceed 0.8 mA, so any power source will last for a long time, even with daily long-term listening to the air.

The design of the receiver depends on the housing you choose. The author used a thread box made of thick plastic (see photo of the receiver in Radio, 2003, No. 1) with dimensions of 160x80x40 mm. Actually, the entire receiver is mounted on the front panel, which also serves as a cover for the box. The panel must be cut from one-sided foil-coated getinax or fiberglass. It is advisable to choose a material with a beautiful non-foil surface (the author uses black getinaks). Holes are drilled in the panel for the antenna and grounding sockets, KPI, volume control, then the foil is sanded to a shine with fine sandpaper and washed with soap and water.

The telephone connector is installed on the lower side wall of the box (Fig. 4). The power battery is placed at the bottom of the box and pressed through a cardboard spacer with a bracket made of thin elastic brass or tin, resting against the side walls of the box. The battery terminals are made from ordinary wiring wires. Their stripped ends are inserted into the windows provided in the cardboard battery case before installing the battery in the receiver. The negative terminal is soldered to the body of the telephone connector, the positive terminal to socket 2. The connector is connected to the receiver board with four twisted conductors of sufficient length.

Mounting the receiver mounted. Those parts, one terminal of which is connected to a common wire, are soldered with this terminal (shortened to the minimum length) directly to the foil. Then the remaining terminal also serves as a mounting stand, to which the terminals of other parts are soldered, in accordance with the diagram. It is even recommended to bend one of the connected terminals in the form of a ring or mounting tab. If the design of the part allows it (KSO type capacitors, oxide capacitors), it is useful to secure its body to the board with a drop of glue. Other mounting tabs are the terminals of the control unit and the volume control. The spring output from the rotor plates of the KPI must be connected to the foil of the board with a separate conductor - this will eliminate possible frequency jumps when rebuilding the receiver, since the electrical contact through the bearings is by no means the best.

When installing the low-pass filter coil, solder a short piece of single-core mounting wire to the board and bend it perpendicular to the board. A thick cardboard or plastic washer, a coil, and another similar washer are put on it in succession, and everything is secured with a drop of solder. The top end of the support wire must be insulated to prevent the formation of short-circuited turn. If the top washer is made wider, then it is convenient to attach the terminals of capacitors C8 and C11 to it. Even without drilling holes, the lead can be “melted” through the plastic with a soldering iron.

Loop coil frames typically have four pins for mounting on a printed circuit board. Three of them are soldered to the foil of the receiver board, the remaining one is used to secure the “hot” output of the coil and as a mounting tab. The distance between the axes of the coils L1 and L2 should be about 15 mm to obtain optimal connection. If you plan to take the receiver with you on hikes, when wet weather often occurs, it is better to fill the turns of all coils with paraffin. All you need is a soldering iron and a candle stub. The same applies to all cardboard insulating parts.

The approximate location of parts on the receiver board is shown in Fig. 5. An “instrument” version of the receiver design (for home use) is also possible, when the front panel is located vertically, the antenna jack is on the right, and the volume control is on the left. In this case, it is advisable to install the telephone connector on the front panel on the left, next to the volume control, and make the case out of metal to protect it from interference created by other equipment standing on the table.

For other receiver designs, the following must be observed: general rules: input circuits and circuits should not be placed close to the local oscillator; it is better to place them on opposite sides of the KPI, the body of which will serve as a natural screen; the local oscillator coil should not be placed close to the edge of the board to prevent the influence of hands on the frequency; The input and output circuits of the ultrasonic sounder should be spaced further apart to reduce the likelihood of its self-excitation. At the same time, the connecting conductors should be short and laid close to the metallized surface of the board. It is better to do without connecting conductors altogether, using only the leads of the parts. The more metal connected to the common wire in the structure, the better. It is easy to see from the illustrations that these rules are observed in the proposed design.

Setting up the receiver is simple and comes down to setting the required local oscillator frequency and adjusting the input circuits to maximize the signal. But before turning on the receiver, carefully check the installation and eliminate any errors found. The functionality of the ultrasonic filter is verified by touching one of the terminals of the low-pass filter coil. A loud "growling" sound should be heard in the phones. In operating mode, the noise from the first stage will be faintly audible.

The easiest way to check the operation of the local oscillator and set its tuning range is 0.9...1 MHz using any broadcast receiver with a mid-wave range. In this receiver, the local oscillator signal will be heard as a powerful radio station during transmission pauses. The receiver with a magnetic antenna must be placed nearby, and if the receiver only has a socket for connecting an external antenna (such receivers are now a rarity), then a piece of wire must be inserted into it, connected to the local oscillator coil. In the absence of generation, it is necessary to install transistor VT1 with a high current transfer coefficient and/or solder resistor R2 of lower resistance. You can clarify the scale calibration of the auxiliary receiver using signals from local radio stations whose frequencies are known. In the center of Russia - "Radio Russia" (873 kHz), "Free Russia" (918 kHz), "Radio Church" (963 kHz), "Slavyanka" (990 kHz), "Resonance" or "People's Wave" (1017 kHz) .

These same signals can be used to calibrate the scale of our receiver. The technique is as follows: tune the auxiliary receiver to the frequency of the radio station, turn on the tuned receiver and change the frequency of its local oscillator using the tuning knob and the L3 coil trimmer until the local oscillator signal is superimposed on the station signal. A whistle will be heard in the loudspeaker of the auxiliary receiver - the beating of two signals. Continuing the adjustment, lower its tone to zero beats and mark a point on the scale - here the tuning frequency of our receiver is exactly equal to twice the frequency of the radio station. If the station signal in the auxiliary receiver is completely clogged with the signal of our local oscillator, slightly increase the distance between the receivers.

The last operation is to configure the input circuits. Connect an antenna at least 5 m long, or even an indoor one. Surely you will already receive some signals. By alternately rotating the trimmers of coils L1 and L2, achieve maximum reception volume. It is more convenient to finally adjust the input circuits in a part of the range free from radio stations, simply to the maximum noise level. It should be noted that adjusting the L2C7 circuit slightly affects the local oscillator frequency, but when tuning for noise this does not make any difference. You can verify that the settings are correct by connecting and disconnecting the antenna: the noise on the air should be many times greater than the internal noise of the receiver.

Receiver operation test results. Its sensitivity, measured using a standard signal generator (SSG), turned out to be about 3 μV. This is not surprising, given the high gain of ultrasonic frequencies (more than 10,000) and the presence of sensitive phones. The receiver mixer introduces virtually no noise of its own, and there is no amplifier in it.

It is preferable to listen to the broadcast in the evening and at night, when the range of 160 meters is “open” (there is a long range of radio waves). During the daytime, you can only hear local stations if they are working (and amateurs, knowing the conditions for the passage of radio waves, usually do not go on the air in this range during the day).

At this time, not having an antenna for the 160-meter range, the author tested the receiver with a temporary wire antenna no more than 10 m long, including descent. It was stretched from the balcony to the roof railing and there fixed on a pole no more than 1.5 m high. Nevertheless, SSB stations in the European part of Russia from Karelia to the Volga region and Krasnodar Territory, as well as Ukraine and Belarus were confidently received. Telegraphs could be heard from stations in Spain and Siberia (I’m only mentioning the most distant ones). “Grounding” to a heating radiator or water pipe significantly increased the reception volume. Thus, almost everything that could be heard on any other, much more complex receiver was accepted.

Literature:

1. Radio magazine, 2003, No. 1, p. 58-60
2. Radio magazine, 2003, No. 2, p. 58-59
3. (in DjVu format)

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. 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 - any factory one, with an inductance of 10 µH and above. 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 economical, and yet in many settlements 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.

We will use an HF converter, resulting in a short-wave double-conversion superheterodyne with a variable first IF and a quartzed first local oscillator. This solution, with a relatively low IF, provides not only good selectivity for both the adjacent channel and the mirror channel throughout the entire HF range, but also high stability of the tuning frequency. Due to this, a similar structure for constructing HF receivers (and transceivers, for example the legendary UW3DI) was very popular in the pre-synthesizer era. Since the expansion of the number of HF bands of such a receiver is limited only by the availability of quartz for the first local oscillator at the required frequencies, which, as in the old days, and, unfortunately, now, in the current difficult economic conditions, represents a certain problem, a converter was developed that covers the main HF ranges on only one (maximum two) quartz resonators. I have already implemented a similar solution in two-tube superheterodyne and showed good results.

The schematic diagram of the first version of the HF converter is shown in Fig. 2. and is already familiar to many, because in fact, it is an adaptation for semiconductors, already familiar to us from the above publication of a tube converter.

This is a four-band converter that provides reception on the 80,40,20 and 10m bands. Moreover, on 80m it performs the functions of a resonant UHF, and on the rest - a converter with a quartz local oscillator. A local oscillator, stabilized by just one non-deficient 10.7 MHz quartz (a resonant frequency in the range of 10.6-10.7 MHz is acceptable without significant differences in operation), operates on 40m and 20m on the fundamental harmonic of quartz, and on the 10th range on its third harmonic (32 ,1MHz). The scale can be a simple mechanical one with a width of 500 kHz on the ranges 80 and 20 m - direct, and 40 and 10 - reverse (similar to that used in UW3DI). To ensure the frequency ranges indicated in the diagram, the tuning range of the basic single-band receiver described in the first part of the article was chosen to be 3.3-3.8 MHz.

The signal from the antenna connector XW1 is fed to an adjustable attenuator made on a dual potentiometer 0R1 and then through the coupling coil L1 goes to a dual-circuit bandpass filter (BPF) L2C3C8, L3C19 with capacitive coupling through capacitor C12. In view of the fact that an antenna of any random length can be used with the receiver, and even when adjusted by an attenuator, the resistance of the signal source at the PDF input can change in wide range In order to obtain a fairly stable frequency response under such conditions, a matching resistor R1 is installed at the PDF input. The ranges are switched using the SA1 switch. In the contact position shown in the diagram, the 28 MHz band is turned on. When switching to 14 MHz, additional loop capacitors C2, C7 and C16, C18 are connected to the circuits, shifting the resonant frequencies of the circuits to the middle of the operating range and an additional coupling capacitor C11. When switching to the 7 MHz range, additional loop capacitors C1, C6 and C15, C17 are connected, shifting the resonant frequencies of the circuits to the middle of the operating range and an additional coupling capacitor C10. When switching to the 3.5 MHz range, capacitors C5, C14 and C9 are connected to the PDF circuits, respectively. To expand the band on the 80 m band, resistor R4 was introduced. This four-band PDF is designed for the use of a large, full-size antenna and is made according to a simplified design using only two coils, which turned out to be possible thanks to several features - the upper ranges, where greater sensitivity and selectivity are required, are narrow (less than 3%), the lower 80 m, where very the level of interference is high and a sensitivity of about 3-5 μV is quite sufficient - wide (9%). The applied circuit has the highest voltage gain at 28 MHz with an almost proportional frequency reduction towards 3.5 MHz, which reduces some gain redundancy in the lower ranges.

The receiver's local oscillator is made according to a capacitive three-point circuit (Colpitts version) on transistor VT1, connected to the OE. In this circuit, generation of oscillations is possible only with inductive reactance of the resonator circuit, i.e. the oscillation frequency is between the frequencies of serial and parallel resonances, and this condition is valid both at the frequency of the main resonance of quartz and at its odd harmonics. When generating at a fundamental frequency of 10.7 MHz (on the 40 and 20 m ranges), the local oscillator circuit consists of a quartz resonator ZQ1 and capacitors C4, C13. On the 10th range, using switch section SA1.3, inductor L3 with an inductance of 1 μH is connected to the collector circuit VT1 instead of load resistor R3, which, together with C13, the capacitance of the collector junction VT1 and the mounting capacitance, forms a parallel resonant circuit tuned to the frequency of the third harmonic of quartz (approximately 32.1 MHz), which ensures activation of quartz at the third harmonic. Resistor R2 determines and quite rigidly sets (due to deep OOS) the operating mode of transistor VT1 for direct current. The C22R6C24 chain protects the common power circuit from penetration of the local oscillator signal into it.

The selected DFT signal is fed to the mixer - the first gate of the field-effect transistor VT2. Its second gate receives a local oscillator voltage of the order of 1...3 Veff through capacitor C20 (in the 80m range, power is not supplied to the local oscillator and transistor VT2 operates in a typical resonant UHF mode). As a resonant load, the full winding of the communication coil L1 of the base receiver is connected to the drain VT2 (see diagram in Fig. 1), on which the signal of the 1st intermediate frequency (3300 - 3800 kHz) is isolated.

Section SA1.4 of the range switch switches the frequency of the reference local oscillator ( USB signal) so that the reception of the upper sideband, traditional for amateur radio bands, is ensured on the 80 and 40m ranges and the lower - on the 10 and 20 m ranges. The +9V converter supply voltage is stabilized integral stabilizer DA1.

If it is possible to purchase modern small-sized quartz with a fundamental frequency (first harmonic) of 24.7-24.8 MHz, then you can make a converter for 5 ranges (see Fig. 3).
Minor changes in the switching outputs of the SA1 range switch are mainly associated with the introduction of the fifth range. To connect the Makeevskaya digital scale (TSH), a buffer amplifier VT3 and a fifth section of the switch SA1.5 (not shown in the diagram in Fig. 3), which controls the DS counting mode, are provided. The circuit turned out to be simple in appearance, but... just imagine how many wires will need to be run just between the five sections of the SA1 switch and the board!

When repeating the described converters, it is necessary to follow the traditional rules for installing RF devices and ensure a minimum length (no more than 4-5 cm) of the conductors connecting the converter to sections SA1.1, SA1.2 and SA1.3 in order to minimize the reactivity they introduce into the resonant circuits ( when installed in the form of a “web-tangle”, this is mainly inductance), which can significantly complicate the adjustment of the circuits in the upper ranges. It was the failure to comply with these rules that was the reason for the failures of some colleagues in the manufacture of tube super on printed circuit boards.

In order to simplify the design and ensure its good repeatability, a universal design of a 4/5 band converter with electronic range switching was developed, the schematic diagram of which is shown in Fig. 4.

Don't be scared! 🙂 The basis of the converter remains the same. Large quantity additional parts - this is the price for versatility of use and electronic control switching ranges. For the four-band (single-quartz) version, all elements except those shown in orange are installed, and for the two-quartz version, all elements except those shown in green are installed. Switching of the PDF ranges is carried out using relays K1-K4, controlled by a single-section switch SA1 (i.e. only 5 wires grounded by HF). Switching the operating mode and generation frequency of the first local oscillator is carried out by transistor switches VT2, VT3, controlled by a resistive decoder R14, R17, R18, R19. The CB counting mode is controlled by the diode decoder VD3, VD5, VD6, VD7, VD10, and the received side is switched by the diode decoder VD4, VD8, VD9. These control algorithms are shown in the tables in Fig. 5.

It also reflects Features of connecting the Makeevskaya digital scale. In the old version of the TsSh (see. description), which is used in the author’s version, to set the required counting formula (see Fig. 5) in three-input mode, two control signals F8 and F9 are used. In the modern version of TsSh Makeevskaya with LED indicators called “Unique LED” (see. description) the continuity of control of the counting mode is preserved and the corresponding pins are called K1 and K2 (shown in brackets in the diagram in Fig. 4). But in the modern economical version of the TsSh Makeevskaya with LCD indicators called “Unique LCD” (see. description) the counting mode is controlled by only one output, switching either the mode of addition or subtraction of all arguments (i.e., the measured frequencies of three generators), but the counting formula we need can be pre-programmed and stored in non-volatile memory - in our case (see table Fig.6) it is necessary to indicate that argument F3 is always negative. The same single-pin control of the counting mode is also supported by the Unique LED digital switch, so that if desired, it can be programmed and connected in the same way as the Unique LCD digital switch.

Converter design. All converter parts are mounted on a board made of single-sided foil fiberglass laminate measuring 75x75 mm. Her drawing in lay format Can . In order to reduce the size, the board is designed to install mainly SMD components - resistors of standard size 1206, and capacitors 0805, imported small-sized electrolytic ones. Trimmers CVN6 from BARONS or similar small-sized ones. Relays with an operating voltage of 12 V are small-sized imported relays with 2 switching groups of a widely used standard size, produced under different names - N4078, HK19F, G5V-2, etc. As VT1, VT5 you can use almost any silicon n-p-n transistors with a current transfer coefficient of less than 100, BC847-BC850, MMBT3904, MMBT2222, etc., as VT2, VT3 you can use almost any silicon p-n-p transistors with a current transfer coefficient of less than 100, BC857-BC860, MMBT3906, etc. Diodes VD1-VD10 can be replaced with domestic KD521, KD522. The receiver coils L1-L4 are made on frames with a diameter of 7.5-8.5 mm with an SCR trimmer and a standard screen from the IF circuits of the color block of Soviet color televisions. Coils L2-L3 contain 13 turns of PEL, PEV wire with a diameter of 0.13-0.3 mm, wound turn to turn. Communication coil L1 is wound on top of the bottom of coil L2 and contains 2 turns, and communication coil L4 is wound on top of the bottom of coil L3 and contains 7 turns of the same wire. Choke L5, used in a single-quartz version, is a small-sized imported one (green striped). If necessary, all coils can be made on any other frames available to the radio amateur, of course changing the number of turns to obtain the required inductance and, accordingly, adjusting the printed circuit board drawing to the new design. Photo of the assembled board.

Settings is also quite simple and standard. After checking the correct installation and DC modes, we connect a tube voltmeter to the VT5 emitter (connector J4) to monitor the local oscillator voltage level alternating current(if you don’t have an industrial one, you can use a simple diode probe, similar to that described in) or an oscilloscope with a bandwidth of at least 30 MHz with a low-capacitance divider (high-resistance probe); in extreme cases, connect it through a small capacitance.

Switching to the 40 and 20m ranges, we check for the presence of an alternating voltage level of about 1-2 Veff. We similarly check the operation of the local oscillator on the 15 and 10m bands. This is for a two-quartz version, but if we make a single-quartz (quad-band) version, then we turn on the 10m range and by adjusting C25 we achieve the maximum generation voltage - it should be approximately the same level. Then, by connecting a frequency meter (FC) to connector J4, we check the local oscillator generation frequencies for compliance with the data in the table shown in Fig. 5.

If you have devices such as frequency response meter or GSS, or better yet NWT, it is better to configure the PDF independently from the base receiver. To do this, we temporarily close the resistor R5 with a wire jumper, so that the local oscillator signal does not interfere with us, and connect it to connector J2 load resistor 220 ohms, and to it the NWT input (or an output indicator, for example an oscilloscope with a bandwidth of at least 30 MHz with a low-capacitance divider (high-resistance probe) with a sensitivity no worse than tens of mV). We connect the NWT output (GSS or frequency response meter) to the antenna input. For correct measurements, we set its output level so that there is no noticeable overload of the two-gate transistor, which in this case works as a UHF. The absence of overload can be determined by the unchanged frequency response when the signal decreases, for example, by 10 dB or, in the case of using GSS, the proportionality of the change in its output level to the change in the input level, even by the same 10 dB. It is recommended to carry out such a check (to ensure that the measuring path is not overloaded) regularly., so as not to step on the typical rake for beginners.

And we move on to setting up the PDF, starting from the 80m range. By adjusting the trimmers of coils L2, L3, we achieve the required frequency response on the screen (if we configure it using the GSS, then we set the average frequency of the range to 3.65 MHz on it and achieve the maximum output signal). Then we move on to setting up the PDF on other bands, starting from 10m, but we don’t touch the coil cores anymore! And we adjust the trimmers corresponding to the ranges - on the range of 10m - these are C5, C20, 15m - C10, C19, 20m - C9, C18, and 40m - C8, C17.

The interconnection diagram is shown in Fig. 6. The +5V power supply is provided by an external integrated stabilizer 0DA1, mounted on the metal body of the receiver for better cooling. Filter 0С2.0R3 provides decoupling of the digital switch supply and reduces the heating of the 0DA1 stabilizer when using digital switch with LED indicators, consuming up to 200 mA. When connecting the economical “Unique LCD” digital switch, which consumes only 18 mA, the recommended filter ratings are indicated in parentheses, and the permissible power dissipation of resistor 0R3 can be reduced to 0.125 W. After connecting the converter (if the boards were configured separately from each other) to the base receiver, you need to check whether the pairing of the first circuit of the 1st IF (on coil L2 Fig. 1.) has gone missing and, if necessary, adjust it according to the method outlined in the first part of the article. It is better to do this on some wide range, for example on 10 or 15m, so that the PDF does not significantly limit the bandwidth of the entire RF/IF path of the receiver when tuning across the entire range of the 1st IF.

Photo of the appearance of the assembled five-band receiver

photo of its installation:

A correctly configured receiver has a sensitivity at s/n = 10 dB no worse (probably noticeably better, but I can’t measure it more accurately with the equipment now available) 0.4 µV (10m) to 2 µV (80m). For a long time the receiver was tested with a surrogate antenna (15 meters of wire from the 4th floor to a tree), I like how it works. Thanks to the wonderful GDR-rovsky EMF, it sounds juicy and beautiful (as long as the frequency neighbors don’t interfere 🙂), efficient (I almost never use an attenuator) and the AGC works smoothly, the GPA frequency is quite stable without any thermal stabilization work, the initial run-out is less than 1 kHz, therefore, immediately upon switching on, the Makeevskaya DAC is activated and you can use the receiver without any warm-up - the frequency stands rooted to the spot during any switching of bands.

You can discuss the design of the receiver, express your opinion and suggestions at forum

S. Belenetsky,US5MSQ Kiev, Ukraine

This is the simplest (basic) single-band version of a superheterodyne receiver. Its circuit diagram is shown in Fig. 2.

The input signal of the amateur band 80 m (frequency band 3.5...3.8 MHz) with a value of at least 1 μV is supplied to the adjustable attenuator 0R1, made on a dual potentiometer. Compared to a single potentiometer, this solution provides greater attenuation control depth (more than 60 dB) throughout the entire HF range, which allows for optimal receiver operation with almost any antenna. Next, the signal is fed to the input double-circuit bandpass filter (DFT), formed by inductors LI, L2 and capacitors C2, C3, C5, C6 with external capacitive coupling through capacitor C4. The connection to the primary circuit shown in the diagram through a capacitive divider C2, C3 is recommended for a low-impedance antenna (quarter-wave “beam” about 20 m long, dipole or “delta” with a coaxial cable feeder). For a high-impedance antenna in the form of a piece of wire with a length significantly less than a quarter of the wavelength, the output of the attenuator 0R1 is connected to the terminal of the X1 board, connected to the first circuit (L1, C2, C3) of the input filter through capacitor C1. The connection method for each antenna is selected experimentally based on maximum volume and reception quality.

The circuit of this dual-circuit PDF is optimized for an antenna resistance of 50 Ohms and a load resistance (R4) of 200 Ohms. Moreover, its transmission coefficient due to the transformation of resistances is approximately +3 dB, which ensures high sensitivity - no worse than 1 µV. In view of the fact that an antenna of any random length can be used with the receiver, and even when adjusted by an attenuator, the resistance of the signal source at the PDF input can vary over a wide range, in order to obtain a fairly stable frequency response under such conditions, a matching resistor R1 is installed at the PDF input. The coils used are ready-made small-sized chokes of standard ratings, which are cheap, already widely available and, most importantly, you can abandon the homemade coils that are so disliked by many beginning radio amateurs.

The selected DFT signal with a value of at least 1.4 μV is supplied to the first gate of the field-effect transistor VT1. Its second gate receives a local oscillator voltage of the order of 1...3 Veff through capacitor C7. An intermediate frequency signal (500 kHz), which is the difference between the frequencies of the local oscillator and the signal, a value of the order of 25...35 μV, is allocated in the mixer drain circuit by a circuit formed by the inductance of the EMF winding Z1 and capacitors C12, C15. The decoupling chains R11, C11 and R21, C21 protect the general power supply circuit of the mixers from local oscillator, intermediate and audio frequency signals entering it.

The first local oscillator of the receiver is made according to a capacitive three-point circuit (Clapp version) on transistor VT2. The local oscillator circuit is made up of inductor L3 and capacitor C8, C9, C10. The local oscillator frequency can be tuned (with some margin at the edges) in the range of 4000-4300 kHz using a variable capacitor (KPE) 0C1. Resistors R2, R5 and R7 determine and rigidly set (due to deep OOS) the direct current operating mode of the transistor, which ensures high frequency stability. Resistor R6 improves the spectral purity (shape) of the signal. The +6 V power supply of both local oscillators is stabilized by the DA1 integrated stabilizer. Chains R10, C14, C16 and R12, C17 protect the common power supply circuit of both local oscillators and decouple them from each other.

The main signal selection in the receiver is performed by the Z1 EMF with a bandwidth of 2.75 kHz with an average bandwidth. Depending on the type of EMF used, the selectivity in the adjacent channel (when detuned by 3 kHz above or below the passband) reaches 60...70 dB. From its output winding, tuned by capacitors C19, C22 to resonance at an intermediate frequency, the signal is supplied to the detector, which is made according to a circuit similar to the first mixer, using a field-effect transistor VT4. Its high input impedance made it possible to obtain the minimum possible signal attenuation in the main selection EMF (about 10-12 dB), so at the first gate the signal value is at least 8...10 µV.

The second local oscillator of the receiver is made on transistor VT3 in almost the same circuit as the first, only instead of inductance a ceramic resonator ZQ1 is used. In this circuit, the generation of oscillations is possible only with the inductive reactance of the resonator circuit, i.e., the oscillation frequency is between the frequencies of series and parallel resonances. Often in such receivers a rather scarce set is used in the second local oscillator - quartz resonator at 500 kHz and EMF with upper passband. This is convenient, but it significantly increases the cost of the receiver.

Our receiver uses a widely used 500 kHz ceramic resonator from remote controls as a frequency-setting element, which has a fairly wide inter-resonance interval (at least 12-15 kHz). By adjusting the capacitance of capacitors C23, C24, the second local oscillator easily “stretches” the frequency in the range of at least 493-503 kHz and, as experience has shown, with the exception of direct temperature effects, it provides frequency stability sufficient for practice. Thanks to this property, almost any EMF with an average frequency of about 500 kHz and a bandwidth of 2.1...3.1 kHz is suitable for our receiver. This could be, say, EMF-11D-500-3.0V or EMFDP-500N-3.1 or FEM-036-500-2.75S, used by the author, with letter indices V, N, S. The letter index indicates which sideband relative to the carrier is allocated by this filter - upper (B) or lower (H), or whether the frequency of 500 kHz falls in the middle (C) of the filter passband. In our receiver this does not matter, since during setup the frequency of the second local oscillator is set 300 Hz below the filter passband, and in any case the upper sideband will be highlighted. The required frequency of the second local oscillator for a specific EMF with a bandwidth P (kHz) can be determined using the simplest formulas:

For EMF with the upper band F=500 kHz;

With middle band F(kHz)=499.7 - P/2;

With the lower band F(kHz)=499.4 - P.

The signal voltage of the second local oscillator with a frequency of about 500 kHz (in the author’s copy 498.33 kHz) and a value of the order of 1.5 ... 3 Veff is supplied to the second gate VT4 and, as a result of conversion, the spectrum of the single-sideband signal is transferred from the IF to the audio frequency region. The conversion factor (gain) of the detector is approximately 4.

The amplified ultrasonic signal is detected by diodes VD1, VD2, and the AGC control voltage is supplied to the gate circuit of the regulating VT5.

As soon as the value of the regulating voltage exceeds the threshold (approximately 1 V), the transistor opens and the voltage divider formed by it together with resistor R20, due to the excellent threshold properties of such a regulator, very effectively stabilizes the output audio frequency signal at a level of approximately 0.65-0.7 Veff, which corresponds to a maximum output power of approximately 60 mW, and at 16 ohm - 30 mW and the receiver will be quite economical. With such power, modern imported speakers with high efficiency are capable of sounding a three-room apartment, but for some domestic speakers it may seem not enough, then you can increase the AGC threshold by 2 times by installing red LEDs as VD1, VD2, while the ULF power will need to be raised to 12 V.

In rest mode or when working with high-impedance headphones, the receiver is quite economical - it consumes about 12 mA. At maximum sound volume of a dynamic head with a resistance of 8 Ohms connected to its output, the current consumption can reach 45 mA.

The power supply is suitable for any industrial production or homemade one, providing a stabilized voltage of +9...12 V at a current of at least 50 mA.

For autonomous power supply, it is convenient to use batteries placed in a special container or rechargeable batteries. For example, an 8.4 V battery the size of a Krona with a capacity of 200 mAh is enough for more than 3 hours of listening to the airwaves on the speaker at medium volume, and when using high-impedance phones - more than 10 hours.

All receiver parts, in addition to connectors, variable resistors and KPIs, are mounted on a board made of single-sided foil fiberglass laminate measuring 45x160 mm. A drawing of the board from the side of the printed conductors is shown in Fig. 3, and the location of the parts is in Fig. 4. Payment in format *.lay can be downloaded from the archive.

Transistors VT1, VT4 can be any of the BF961, BF964, BF980, BF981 series or domestic KP327. Some of these transistors may require selection of source resistors to obtain a drain current of 1...2 mA.

Imported general-purpose transistors are suitable for local oscillators n-p-n type 2SC1815, 2N2222 or domestic KT312, KT3102, KT306, KT316 with any letter indices. Field effect transistor VT1 2N7000 can be replaced with analogues BS170, BSN254, ZVN2120a, KP501a. Diodes VD1, VD2 1N4148 can be replaced with any silicon KD503, KD509, KD521, KD522.

Fixed resistors - any type with a dissipation power of 0.125 or 0.25 W.

Parts mounted mounted on the chassis (see Fig. 5) can be of any type. Potentiometers 0R1 - dual, can have a resistance of 1-3.3 kOhm, 0R2 - 47-500 Ohm. Tuning capacitor 0C1 - preferably small-sized with an air dielectric with a maximum capacity of at least 240 pF. In the absence of such a capacitor, you can use a small-sized KPI transistor broadcast receiver. Of course, it would be useful to equip the tuning capacitor with a simple vernier with a slowdown of 1:3... 1:10.

Ceramic loop capacitors, small-sized ceramic thermostable (with a low temperature coefficient of capacitance (TKE) - groups PZZ, M47 or M75) KD, KT, KM, KLG, KLS, K10-7 or similar imported (orange disk with a black dot or multilayer with zero TKE - MP0). Trimmers CVN6 from BARONS or similar small-sized ones. C26, C29 preferably heat-stable film, metal film, for example, MKT, MKR series and similar. The rest are ceramic blocking and electrolytic ones - any type of imported small-sized ones.

To wind the heterodyne coil L 3, a ready-made frame with a 600NN ferrite trimmer and a screen from standard IF circuits 465 of domestic transistor radios (in particular, from the Alpinist radio receiver) was used, for which the number of turns to obtain the required inductance according to the calculation formula is equal to:

W=11*SQRT(L[µH]),

in our case, to obtain 8.2 μH, 31 turns of wire with a diameter of 0.17-0.27 mm are required.

After winding the coil evenly in 3 sections, a trimmer is screwed into the frame, and then this structure is enclosed in an aluminum screen, while the standard cylindrical magnetic circuit is not used.

In general, any available to a radio amateur will be suitable as a frame for homemade coils, of course with appropriate adjustments to the printed conductors:

Very convenient and thermally stable are imported 455 kHz IF circuits, similar to the one used in, the trimmer of which is a ferrite pot having a thread on the outer surface and a slot for a screwdriver, the number of turns to obtain the required inductance is W=6*SQRT(L[µH]),

in this case, to obtain 8.2 μH, 17 turns of wire with a diameter of 0.17-0.27 mm are required.

For popular armor cores of the SB-12a type, the formula for calculating the number of turns to obtain the required inductance is W=6.7*SQRT(L[µH]),

in this case, to obtain 8.2 μH, 19 turns of wire with a diameter of 0.17-0.27 mm are required.

If ready-made frames with a diameter of 7.5 mm with SCR trimmers and screens from the IF circuits of the color blocks of television receivers are used, then with a winding length of 8 mm (with a small number of turns, we wind the winding turn to turn, and with a large number of turns, in bulk) the formula for calculating the quantity turns to obtain the required inductance is equal to W=14*SQRT(L[µH]),

in this case, to obtain 8.2 μH, 40 turns of wire with a diameter of 0.17-0.27 mm are required.

As noted above, in the PDF, standard imported small-sized EC24 type chokes and similar ones are used as inductors. Of course, if it is problematic to purchase ready-made chokes of the required inductance, you can also use homemade coils in the PDF, calculating the number of turns using the above formulas. Conversely, if difficulties arise with winding homemade coils, you can also use a ready-made imported 8.2 µH inductor as L3. Our colleague G. Glukhov (RU3DBT) during the manufacture of this receiver I went this way (Fig. 5) and notes quite satisfactory stability of the VFO frequency.

Any ready-made inductance in the range of 70-200 μH is suitable as an L 4 inductor, but you can also use a homemade one by winding 20-30 turns on a ferrite ring with a diameter of 7-10 mm with a permeability of 600-2000 (a larger number of turns corresponds to smaller diameters and/or permeability).

Setting up. A correctly mounted receiver with serviceable parts begins to work, as a rule, the first time it is turned on. However, it is useful to carry out all receiver setup operations in the sequence outlined below. All controls must be set to maximum signal, and the coil cores in L7, L8 are in the middle position. First, using a multimeter connected to the power supply, we check that the current consumption does not exceed 12-15 mA; the receiver’s own noise should be heard in the speaker. Next, switch the multimeter to measurement mode DC voltage, we measure the voltages at all terminals of microcircuits DA1, DA2 - they must correspond to those given in Table 1.

Table 1

	Voltage, V	Pin No. DA1	Voltage, V
		Pin No. DA2	Voltage, V

Let's carry out simple check general performance of the main components.

If the ULF is working properly, touching pin 3 of DA2 with your hand should cause a loud, growling sound to appear in the speaker. Touching your hand to the common connection point C27, R19, R20 should lead to the appearance of a sound of the same timbre, but noticeably lower volume - this is where the AGC is activated.

We check the DPT drain currents by the voltage drop across the source resistors R9 and R16, if it exceeds 0.44 V, i.e. The drain current of the DPT exceeds 2 mA; it is necessary to increase the resistance of the source resistors to reduce the current to a level of the order of 1-1.5 mA.

To set the calculated frequency of the second local oscillator, remove the technological jumper (jumper) J2 and instead connect a frequency meter to this connector. In this case, VT4 performs the function of a decoupling (buffer) amplifier of the signal of the second local oscillator, which almost completely eliminates the influence of the frequency meter on the frequency setting accuracy. This is convenient not only at the setup stage, but later, during operation, it will allow for operational monitoring, and, if necessary, adjustment of local oscillator frequencies without completely disassembling the receiver. We achieve the required frequency by selecting C24 (roughly) and adjusting the trimmer C23 (exactly). We return the jumper (jumper) J2 to its place and similarly, by connecting the frequency meter instead of the process jumper (jumper) J1, we check and, if necessary, adjust (by adjusting the inductance L3) the GPA tuning range, which should not be narrower than 3980-4320 kHz. If the tuning range of the GPA turns out to be too wide, which is quite likely when using a KPI with a larger maximum capacitance, you can connect an additional stretching capacitor in series with it, the required capacitance of which will need to be selected independently.

To tune the input and output excitation windings of the EMF into resonance, an unmodulated signal with a frequency corresponding to the middle of the EMF passband (in the author’s version - 500 kHz) is supplied from the GSS to the first gate of transistor VT1 (in the author’s version - 500 kHz) and by selecting the size of the capacitors C12, C22 (roughly) and fine adjustment with trimmers C15, C19 to the maximum output signal. At the same time, in order to avoid triggering of the AGC, the level of the GSS signal is maintained such that the signal at the ULF output does not exceed 0.4 Veff. As a rule, for an EMF of unknown origin, even the approximate value of the resonant capacitance is unknown, and it, depending on the type of EMF, can range from 62 to 150 pF. You can significantly simplify the setup if you first measure the inductance of both EMF coils, for example, using a simple attachment.

Then the resonant capacitance for each coil (and their inductance is by no means the same, the difference can reach 10%, so in my copy of the EMF the inductance was 840 and 897 μH) we can easily determine it using the formula

S[pF]=101320/L[μH].

If the values ​​of the contour elements of the PDF correspond to those indicated on the diagram with an accuracy of no worse than +-5%, additional settings not required. With homemade coils, setting the PDF can be done according to the standard method using GSS.

For normal operation receiver on the 80 m range, it is advisable to connect an external antenna with a length of at least 10-15 m. When powering the receiver from batteries, it is useful to connect a grounding wire or a counterweight wire of the same length.

Good results are obtained by using metal pipes for water supply, heating or balcony railings in panel reinforced concrete buildings as grounding.

Literature.

1. Forum “Simple observer receiver with EMF”

2. Shulgin K. Basic parameters of disk EMFs at a frequency of 500 kHz. - Radio, 2002, No. 5, pp. 59-61.

3. Belenetsky S. Dual-band HF receiver “Malysh”. - Radio, 2008, No. 4, p. 51, No. 5, p. 72. http://www.cqham.ru/trx85_64.htm

4. Belenetsky S. Attachment for measuring inductance in amateur radio practice. - Radio, 2005, No. 5, pp. 26-28. http://www.cqham.ru/ot09_2.htm

Sergey Belenetsky (US5MSQ)

Short wave reception is considered the domain of more complex superheterodyne circuits and solid design experience. Is this why novice radio amateurs avoid high-frequency ranges? And in vain. Let us remember the short-wave amateurs of the early 30s, because they mainly worked with the simplest direct-amplification tube receivers. Of course, the stability of such devices is lower, and their tuning is more “fine”. But simplicity and accessibility may well compensate for the shortcomings for inexperienced radio amateurs. For the first acquaintance with shortwave broadcasting, it is better to make the receiver in the form of a small tabletop structure, and receive it through headphones.

The diagram of such a receiver, capable of operating in the range of approximately 25-41 m, is given in Figure 1. The receiver has one oscillatory circuit, which allows, if necessary, by changing the number of turns of coil L2 and the value of capacitor C2, to shift the boundaries of the range to the frequency region of interest. Transistor VT1 operates in a radio frequency amplifier. To increase sensitivity, positive feedback, regulated by variable resistor R3, is supplied from its collector through coil L1 to the loop coil. Next transistor detects the received signal and pre-amplifies its low-frequency component. Transistors VT3, VT4 operate in an audio amplifier, which is loaded with a sensitive high-impedance telephone BF1.

Receiver parts can be located on the circuit board as they are located on schematic diagram, except for resistor R3; It is more convenient to move the control handle of the latter to the left of the vernier handle, which rotates the rotor of the tuning capacitor C3. The antenna can be a piece of mounting wire, the length of which must be determined experimentally. In some cases, satisfactory reception is obtained with a standard telescopic antenna.

The receiver uses fixed resistors of the types MLT, MT, variable (R3) - SP-0.4; permanent capacitors - KLS, PM, KPE (C3 any one- or two-section with a maximum capacity of the same order as those indicated in the diagram). The phone is “two-eared” with a coil resistance of about 1.5-2 kOhm. For switch S1, a regular toggle switch is suitable. It is better to make up the power source from two 336 Planet batteries connected in series.

In addition to the board and case, you will have to make the receiver coils yourself. They are wound on a common plastic frame with a diameter of 6.5-7 mm and a length of about 25 mm. Coil L2 has 23 turns of PEV-0.44 wire; L1 - about 5 turns of PELSHO-0.2 wire. The tuning knob axis - also known as the vernier drive axis - can be made from an old variable resistor with remote turn stop. This design of the unit will make it easy to secure it with a nut on the board, moving it away from the installation and thereby reducing the influence of hands on adjustments. The layout diagram of the receiver is shown in Figure 2.

After checking the correct assembly and current values ​​of the transistors (they are specified by selecting elements R1, R4, R7), make sure that the feedback operates normally within the entire range. Close to the far right position of the feedback knob, a whistle should occur in the phone. If this does not happen, increase the number of turns of L1. The generation will be “extinguished” with the control knob, but if this fails, reduce the number of turns or move them further away from L2. It happens that instead of generation, the signal is weakened, then you need to swap the L1 pins.

Reception to the generator, which is our receiver, is carried out as follows. Slowly rebuilding the circuit, at the same time using the feedback knob to maintain it at a level close to the breakdown in generation. This ensures the highest sensitivity of the receiver to weak signals. The generation that has begun must be stopped immediately, otherwise the sound quality of the self-excited receiver will sharply deteriorate.

With careful tuning on our receiver, you can catch many radio stations broadcasting on the HF band.

Young Technician 1993 No. 2