Diagram of a simple HF observer receiver for any amateur radio band
Good afternoon, dear radio amateurs!
Welcome to the website ““
Today we will look at a very simple circuit that at the same time provides good performance - HF observer receiver - shortwave.
The scheme was developed by S. Andreev. I cannot help but note that no matter how many developments I have seen in the amateur radio literature of this author, they were all original, simple, with excellent characteristics and, most importantly, accessible for repetition by beginning radio amateurs.
The first step of a radio amateur into the elements usually always begins with observing the work of other radio amateurs on the air. It is not enough to know the theory of amateur radio communications. Only by listening to amateur radio, delving into the basics and principles of radio communications, can a radio amateur gain practical skills in conducting amateur radio communications. This scheme is precisely intended for those who want to take their first steps in amateur communications.
Submitted circuit diagram of an amateur radio receiver - shortwave very simple, made on the most accessible element base, easy to configure and at the same time providing good characteristics. Naturally, due to its simplicity, this circuit does not have “stunning” capabilities, but (for example, the sensitivity of the receiver is about 8 microvolts) it will allow a novice radio amateur to comfortably study the principles of radio communication, especially in the 160-meter range:
The receiver, in principle, can operate in any amateur radio band - it all depends on the parameters of the input and heterodyne circuits. The author of this scheme tested the operation of the receiver only for the ranges of 160, 80 and 40 meters.
For which range is it better to assemble this receiver? To determine this, you need to take into account what area you live in and proceed from the characteristics of amateur bands.
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The receiver is built using a direct conversion circuit. It receives amateur telegraph and telephone stations - CW and SSB.
Antenna. The receiver operates on an unmatched antenna in the form of a piece of mounting wire that can be stretched diagonally under the ceiling of the room. For grounding, a pipe from the water supply or heating system of the house, which is connected to terminal X4, is suitable. The antenna reduction is connected to terminal X1.
Principle of operation. The input signal is isolated by the L1-C1 circuit, which is tuned to the middle of the received range. Then the signal goes to a mixer made of 2 transistors VT1 and VT2, diode-connected, connected back-to-back.
The local oscillator voltage, made on transistor VT5, is supplied to the mixer through capacitor C2. The local oscillator operates at a frequency two times lower than the frequency of the input signal. At the output of the mixer, at connection point C2, a conversion product is formed - a signal of the difference between the input frequency and the doubled frequency of the local oscillator. Since the magnitude of this signal should not be more than three kilohertz (the “human voice” falls within the range of up to 3 kilohertz), then after the mixer a low-pass filter is turned on on inductor L2 and capacitor C3, suppressing a signal with a frequency above 3 kilohertz, thereby achieving high receiver selectivity and the ability to receive CW and SSB. At the same time, AM and FM signals are practically not received, but this is not very important, because radio amateurs mainly use CW and SSB.
The selected low-frequency signal is fed to a two-stage low-frequency amplifier using transistors VT3 and VT4, at the output of which high-impedance electromagnetic telephones of the TON-2 type are switched on. If you only have low-impedance telephones, then they can be connected via a transition transformer, for example from a radio point. In addition, if you connect a 1-2 kOhm resistor in parallel with C7, then the signal from the VT4 collector through a capacitor with a capacity of 0.1-10 μF can be applied to the input of any ULF.
The local oscillator supply voltage is stabilized by a zener diode VD1.
Details. You can use different variable capacitors in the receiver: 10-495, 5-240, 7-180 picofarads, it is desirable that they be with an air dielectric, but they will also work with a solid one.
To wind the loop coils (L1 and L3), frames with a diameter of 8 mm with threaded trimming cores made of carbonyl iron are used (frames from the IF circuits of old tube or tube-semiconductor TVs). The frames are disassembled, unwound and a cylindrical part 30 mm long is cut off. The frames are installed in the holes of the board and fixed with epoxy glue. Coil L2 is wound on a ferrite ring with a diameter of 10-20 mm and contains 200 turns of PEV-0.12 wire, wound in bulk, but evenly. The L2 coil can also be wound on the SB core and then placed inside the SB armor cups, gluing them with epoxy glue.
Schematic representation of the mounting of coils L1, L2 and L3 on the board:
Capacitors C1, C8, C9, C11, C12, C13 must be ceramic, tubular or disk.
Winding data of coils L1 and L3 (PEV wire 0.12) ratings of capacitors C1, C8 and C9 for different ranges and variable capacitors used:
The printed circuit board is made of foil fiberglass. The location of the printed tracks is on one side:
Setting up. The low-frequency amplifier of the receiver, with serviceable parts and error-free installation, does not need adjustment, since the operating modes of transistors VT3 and VT4 are set automatically.
The main setup of the receiver is the setup of the local oscillator.
First you need to check the presence of generation by the presence of RF voltage at the tap of coil L3. The collector current VT5 should be within 1.5-3 mA (set by resistor R4). The presence of generation can be checked by the change in this current when touching the heterodyne circuit with your hands.
By adjusting the local oscillator circuit, it is necessary to ensure the required frequency overlap of the local oscillator; the local oscillator frequency must be adjusted within the ranges:
– 160 meters – 0.9-0.99 MHz
– 80 meters – 1.7-1.85 MHz
– 40 meters – 3.5-3.6 MHz
The easiest way to do this is to measure the frequency at the tap of the L3 coil using a frequency meter capable of measuring frequencies up to 4 MHz. But you can also use a resonant wavemeter or an RF generator (beat method).
If you are using an RF generator, you can also configure the input circuit at the same time. Apply a signal from the HHF to the receiver input (place the wire connected to X1 next to the generator output cable). The RF generator must be tuned within frequencies twice as high as those indicated above (for example, on the range of 160 meters - 1.8-1.98 MHz), and the local oscillator circuit must be adjusted so that, with the appropriate position of the capacitor C10, sound with a frequency of 0.5-1 kHz. Then, tune the generator to the middle of the range, tune the receiver to it, and adjust the L1-C1 circuit to the maximum sensitivity of the receiver. You can also calibrate the receiver scale using the generator.
In the absence of an RF generator, the input circuit can be configured by receiving a signal from an amateur radio station operating as close to the middle of the range as possible.
In the process of setting up the circuits, it may be necessary to adjust the number of turns of coils L1 and L3. capacitors C1, C9.
Excellent circuit based on a field-effect transistor. It showed good stability, low consumption and very good sound sensitivity. Does not contain scarce parts and is easily repeatable.
Almost all radio components are SMD size 0805. Coil L1 consists of 4.5-5.5 turns of 0.4-0.5 mm wire, wound on a mandrel with a diameter of 4 mm.
Schematic diagram:
PCB options: 
Attention! The circuit is capricious in terms of installation quality and PCB layout. To avoid stepping on someone else’s rake, use a proven seal and thoroughly wash off all the flux. Two proven versions of printed circuit boards can be downloaded from. The boards were created in the program.
The operating frequency is set by the circuit parameters L1, C6, C7 (the diagram shows the ratings for a frequency of ~100 MHz).
To increase the operating frequency to 400-433 MHz it is necessary to use the following ratings: C6 - 6.8 pF, C7 - 18 pF, L1 - 2.5 vit of wire 0.4-0.5 mm on a 2 mm mandrel, connection with varicap C5 - 2.2...3.3 pF. It also makes sense to reduce the capacitance between the antenna and drain to 1-3 pF.
Any miniature electret microphone (from intercoms, Chinese radios, etc.). 
The negative is usually connected to the body. Microphones should be checked by “blowing”: turn on the tester in resistance measurement mode and blow into the microphone; if the resistance changes, it means it’s working.
If you have a microphone from an old Samsung S100 phone, then take it - you will get a very strong sensitivity of the radio microphone (every rustle will be heard).
As an antenna, a piece of wire a quarter of a wavelength long (at 100 MHz ~70 cm, at 400 MHz ~19 cm).
Varicap BB135 can be replaced with BB134. You can also use BB133, but then you will have to reduce the coupling capacitance with the varicap (at 400 MHz set to 1.5-2.2 pF, and at 100 MHz - 5.6-6.8 pF). Otherwise there will be overmodulation.
Transistor BC847 can be replaced with analogues: BC846, BC850, MMBTA05, MMBTA06, MMBTA42. They all have the same pinout. 
The CR2032 battery lasts for approximately 6-8 hours of continuous operation (the current consumed by the circuit is 2.5-4 mA). A lithium-ion battery from a mobile phone will last for several weeks.
The radio microphone is assembled on a board made of double-sided fiberglass 1.5 mm thick. It is necessary to connect the ground on both sides through through holes in the board (the larger the better). To reduce the influence of surrounding objects on the frequency of the bug, the installation elements can be covered with a 4-6 mm high screen made of tinned sheet metal. To improve stability and increase radiated power, it is recommended to use silver-plated wire to wind the L1 coil.
Assembled radio microphones: 
The repeatability of the device is very good; with proper and high-quality installation, it starts working immediately. You only need to adjust the frequency by stretching/compressing the turns of coil L1. No further settings are required.
If it doesn’t work, look for errors in installation, snot in soldering, faulty or incorrectly sealed parts. It is possible that the circuit works, but the signal just does not fall within the range of your receiver. This is where a field indicator (wave meter) would be very useful to you.
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
Receiver from a series of protozoa, with minimum quantity details, 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 higher value. 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.
Schematic diagram of the HF receiver
Here is a description of a simple direct conversion receiver designed to receive amateur radio stations in the range of 80 meters (3.5...3.8 MHz). The receiver is powered by a 9V battery. With its help, you can receive CW and SSB radio stations in offline mode, for example, while working on an expedition or while relaxing in nature.
Provided good adjustment, the receiver has a sensitivity of no worse than 0.5 µV with a signal-to-noise ratio of 12 dB. This makes it possible to reliably receive long-distance radio stations using simple surrogate antennas, even an ordinary piece of mounting wire thrown onto a tree or suspended from a window frame.
Connectors X1 and X2 are used to connect grounding and antenna. The signal from the antenna goes to the input bandpass filter L1-L3, C1-C4. Capacitors C1 and C2 form a capacitive transformer, which reduces the influence of the capacitance of the surrogate antenna on the circuit tuning.
The bandpass filter suppresses interference coming from other ranges, eliminating interference from receiving signals at local oscillator harmonics. From the L3-C4 circuit, the signal goes to the amplifier stage on the field-effect transistor VT1. The use of a field-effect transistor in the RF circuit allows you to expand the dynamic range of the circuit, as well as optimally match the low-impedance input of the diode mixer VD1-VD2 with the circuit L3-C4. Without a field-effect transistor, to match the circuit with the mixer, it would be necessary to use an autotransformer or transformer connection, in which the voltage of the signal supplied to the mixer would be reduced, and, accordingly, the sensitivity.
From the source of the field-effect transistor VT1, the signal is supplied to a mixer using back-to-back diodes VD1 and VD2. The use of back-to-back connections makes it possible to reduce the local oscillator frequency by half, since the conversion occurs on both half-waves of the local oscillator signal.
The local oscillator is made on transistor VT2. The local oscillator frequency is determined by the circuit L4-C11, C10, C8. The variable capacitor CY used here with an air dielectric (from an old receiver) has too much overlap in capacitance for reception in the range of 80 meters, therefore, the overlap is limited by the series-connected C8. Now the capacitance overlap is about 9-150 pF.
The local oscillator operates at a frequency two times lower than the frequency of the received signal. In this case, it is tuned within the range of 1.75-1.9 MHz, which corresponds to reception in the range of 3.5-3.8 MHz.
The local oscillator voltage is removed from tap L4 and supplied to the diode mixer. The local oscillator input of this mixer is also its output. Choke L5 performs two functions, firstly, it separates the high-frequency component of the local oscillator and the conversion results. Secondly, it forms a low-pass filter with capacitor C15.
In general, at the connection point between VD1, VD2 and inductor L5 there is a whole complex of different frequencies, including the input frequency, the local oscillator frequency, the products of addition and subtraction of these frequencies. The low-pass filter (L5-C15) from this entire complex selects only the low-frequency signal as a result of subtracting the input frequency signals and the doubled local oscillator signal. Through an additional filter chain C16-R6-C18, the demodulation product - the low-frequency signal is supplied to the low-frequency amplifier on a type A1 chip K174UN7. This is already very outdated domestic microcircuit ULF, which was actively used in domestic semiconductor televisions of the 80s of the last century.
Variable resistor R8 is used to adjust the ULF gain on chip A1.
At the output, a small-sized speaker 5GDSH-1001 is connected through the isolation capacitor C22. Also very old, elliptical, also used in old semiconductor Soviet televisions.
Power is provided only from the battery. As practice shows, this is the best option for a direct conversion receiver, since any network adapter, when working with a direct conversion receiver, in which the main signal amplification occurs at a low frequency, is a powerful source of interference in the form of network noise. It happens that when operating from the mains, the actual sensitivity of the direct conversion receiver drops several tens of times.
For winding contour coils, frames with a diameter of 8 mm with carbonyl iron cores are used. Such frames can be made from the IF circuits of old tube black-and-white TVs. The frame of such a circuit is a rather massive base with contacts and a long threaded tube, inside of which there are two threaded cores. From one such frame you can make two frames for the coils of this receiver (saw off the base, saw the tube in half, and one core in each half).
Coils L1-L3 contain 35 turns of PEV 0.35 wire. L1 and L3 have taps from the 7th turn. The heterodyne coil L4 contains 33 turns of the same wire, with a tap from the 5th turn. All bends are counted from below, according to the diagram. During installation, coils L1-L3 are located in a separate shielded compartment, but so that the distance between the axes of these coils is not less than 30 mm. All loop coils are wound turn to turn.
Inductor L5 is wound on a ferrite ring with an outer diameter of 10 mm made of 2000NM ferrite. You can use a ring of a different diameter, somewhere in the range of 10-20 mm. Ferrite can have a permeability from 400 to 3000. The coil contains 150-200 turns of PEV 0.12 wire. Winding in bulk, evenly along the circumference of the ring.
You can also use another variable capacitor, preferably with an air capacitor, but it is also possible with a solid dielectric (with a solid dielectric, during tuning, a cracking noise may occur from electrification of the dielectric from friction of the plates). If the capacitor is of a different capacity, you need to change the capacitance C8 accordingly.
The receiver is assembled in a three-dimensional manner in a sectional shielded case soldered from foil glass-textile. Installation - “on the heels”.
V.Rubtsov, UN7BV
Astana, Kazakhstan
The generator circuits presented in the article are not intended to operate in the mid-wave radio broadcast range. The circuits can be used in equipment of the 1.9 MHz amateur band, officially approved for operation on the air by registered radio amateurs, i.e. having permission to operate an amateur radio station and a call sign. Some technical solutions from these schemes can be used in the design of amateur radio transmitters, or you can simply be nostalgic for the past - after all, the “radio hooligan youth” is behind the shoulders of many radio amateurs and just radio lovers.
prefix "Hurdy Organ-1"
Figure 1 shows a diagram of the simplest transmitting medium-wave set-top box with AM modulation for a radio receiver. The set-top box uses a 6PCS radio tube, the maximum power dissipation at the anode of which is 20.5 W. Instead of a 6PCS, you can use a 6P6S lamp (the maximum power dissipation at the anode is 13.2 W) - they have the same pinout.
Oscillatory circuit L1С1 is connected between the lamp anode and the control grid. It provides positive feedback of the cascade - one of the conditions necessary for self-excitation of the generator. Power is supplied to the lamp anode through an oscillating circuit (via a tap in the AND coil). Switch SA1 is used to turn the cascade on in transmit mode and turn it off in receive mode.
The supply voltage comes from the anode of the output lamp of the ULF receiver, therefore, when a signal from the microphone is applied to the input of the ULF receiver, amplitude modulation of the HF oscillations generated by the attachment occurs.
Coil L1 is made on an ebonite frame with a diameter of D-30 mm and contains 55 turns of PEL-0.8 wire (turn to turn) with a tap from the 25th turn, counting from the bottom (according to the diagram) output. This attachment worked well, but had one drawback - the tuning capacitor C1 was galvanically connected to the anode of the lamp (and this is unsafe!), so the tuning knob had to be made of a dielectric.
prefix "Sharmanka-2"
Somewhat later, I managed to find a “organ organ” circuit (Fig. 2), devoid of this drawback. In it, a circuit is connected between the control grid and the cathode of the lamp. Moreover, partial inclusion of the cathode into the circuit due to tapping in the coil is used. This scheme is safer, but delivers slightly less power to the antenna than the previous one. Application of variable capacitor C1. allows you to optimally match the I-NW circuit with the antenna.
In this circuit, the 6PZS radio tube can also be replaced with a 6P6S. Coil I is wound on a ceramic mandrel with a diameter of D-32mm with PEL-0.7 wire. The number of turns is 50 (winding is turn to turn with a tap from the middle).
prefix "Hurdy organ-3"
In Fig. 3 is a diagram of another “organ organ”. In it, KPI C2 is galvanically connected to the body through coil L2. If the terminals of this capacitor are accidentally shorted to the housing, nothing dangerous will happen - the generation of the RF signal will just stop.
The output power of this attachment is greater than that of the previous one (about the same as that of the circuit in Fig. 1), because The oscillatory circuit L2-SZ is connected to the lamp anode circuit. Throttle L1 is enclosed in a screen. Coil L2 is wound on a plastic mandrel with a diameter of D-30 mm with PEL-0.8 wire and contains 50 turns of wire wound turn to turn. The tap is from the middle of the winding.
Another one circuit diagram The simplest transmitting attachment on a 6PZS (6P6S) radio tube is shown in Fig. 4.
prefix "Hurdy organ-4"
This circuit differs from the previous ones by the presence of inductor L1 in the anode circuit of the lamp, which made it possible to connect the output circuit to the anode. In this case, the stators of variable capacitors C2 and C5 are connected to a “common” wire, which significantly increases the safety of the device and makes it easier to control the setting elements. Switch SA1 is included in the cathode circuit of the lamp, with which you can adjust the depth of positive feedback, which allows you to quite accurately select the required mode of operation of the cascade. Coil L3 with adjustable inductance allows you to match the resistance of the output circuit with the input impedance of the antenna. This is important because A piece of wire of arbitrary length is often used as an antenna. Coil L2 is wound on a ceramic mandrel with a diameter of D-40mm and has 40 turns of PEL-0.7 wire (winding - turn to turn, taps are evenly distributed along the entire length of the winding), L4 - on a ceramic mandrel with a diameter of D-35mm and has 50 turns of wire PEL-0.6. In the author’s version, coil L1 (choke) has an inductance of 1 µH, L2 - 8 µH, L3 - 250 µH, L4 - 16 µH. I suggest winding L1 on a ceramic frame with a diameter of D-18mm and a length of 95mm with PELIA-0.35 wire (130 turns). The first 15 turns (closest to the anode) should be discharged in increments of 1.5 mm, the rest of the winding should be turn to turn. I recommend making coil L3 similarly to L4, but increasing the number of turns to 100 and making taps from it (11 taps - according to the number of contacts in the switching strip) in order to make it possible to change the inductance of the coil. The taps should be positioned evenly along the length of the coils - this will simplify its design and, at the same time, allow it to maintain its tuning functions.
Tuning to the frequency in this circuit is done using capacitor C2, and the capacitance of capacitor C5 is selected according to the maximum signal at the output, i.e. adjust the output circuit L4-C5 to resonance. This design of the circuit allows you to tune the output circuit not only to the fundamental frequency, but also to its harmonics (most often the third is used). In this way, it is possible to increase the stability of the frequency of the signal generated by the generator, because The local oscillator operates at a frequency three times lower than the frequency of the output signal.
prefix "Sharmanka-5"
Figure 5 shows a hurdy-gurdy circuit made using two 6PCS radio tubes (you can also use 6P6S tubes, but there is no point in this - it is better to use one 6PCS). This circuit provides a more powerful output signal (about twice that of a single tube circuit). The anodes of the lamps are partially included in the generator circuit to reduce the effect of shunting. In the author’s version, it is recommended to wind coils L1-L3 on one ceramic frame with a diameter of D-40mm. Coil L1 contains 32 turns of PEL-0.3 wire, L2 - 41 turns of PEL-0.4 wire, L3 - 58 turns of PEL-0.7 wire. All coils are wound turn to turn. I recommend reducing the number of turns of each coil by 60 percent, otherwise the generation frequency will move from the mid-wave range to the long-wave range. By adjusting the resistance of resistor R1, you can change the operating mode of the radio tubes.
prefix "Hurdy Organ-6"
Figure 6 shows a diagram of a transmitter using two radio tubes. The oscillatory circuit L1-C2 is included in the cathode circuits of the lamps. Coils L1 and L2 are wound on one ceramic frame D-20 mm: And contains 60 turns of PEL-0.3 wire, L2 - 30 turns of PEL-0.4 (winding of both coils is turn to turn). 2-3 turns of mounting wire (in insulation) are wound on top of coil L2, the ends of which are connected to an incandescent light bulb with a voltage of 6.3 V and a current of 0.28 mA (from a flashlight). This simplest chain provides an indication of the presence of RF generation. In addition, a neon light bulb placed close to the coil can be used as an RF indicator. By the intensity of the lamp's glow, one can judge the change in output power when tuning the range or a change in the parameters of the antenna (for example, when tuning it). So, if, when tuning the antenna, the frequency approaches the resonant one, then the light bulb will glow weaker (by the minimum glow one can judge that the antenna is tuned to resonance with the frequency generated by the transmitter, since there is a maximum power take-off). If the antenna breaks, the light bulb will glow as brightly as possible, and if there is a short circuit in the antenna, it may go out completely (this depends on the magnitude of the connection between the output circuit and the antenna, which is determined by the capacitance of the variable capacitor C1). The power switch SA1 also serves as a “receive/transmit” switch.
prefix "Sharmanka-7"
Figure 7 shows a diagram of the transmitting attachment on the GU50 radio tube. A significant difference between this circuit and the previous ones is the increased output power. Amplitude modulation is carried out along the protective grid of the lamp. Using a variable capacitor C5, the set-top box is tuned to the selected frequency, and using a capacitor C1, the output impedance of the transmitter is matched with the input impedance of the antenna. We should not forget that in this circuit one of the plates of the variable capacitor C5 is under a voltage of 800 V, so be very careful and use a control knob made of high-quality dielectric material to adjust the capacitance of this capacitor.
Coil L1 is wound on a ceramic frame D-40 mm and contains 50 turns of PEL-0.7 wire (winding - turn to turn) with a tap from the middle.
prefix "Sharmanka-8"
Figure 8 shows another diagram of a transmitter made on a GU50 radio tube. In it, the generation frequency is set by the L1-C2 circuit, and at the output of the device the so-called P-circuit C7-L2-C8 is used, which makes it possible to very well match the output impedance of the cascade with the input impedance of the antenna. Using a variable capacitor C7, the P-circuit is tuned to resonance (matching the output resistance of the lamp with the resistance of the P-circuit), and using C8, the coupling value with the antenna is selected. Amplitude modulation of the output signal is carried out along the protective grid of the lamp.
Chain C3-VD1-R2 are elements for protecting speaker circuits from RF interference. By selecting the resistance of the resistors (within 0.5-1 MOhm) and R3, you can select the optimal mode of operation of the lamp.
Coil L1 is wound on a cylindrical ceramic frame D-40 mm with PEL wire 0.9 and contains 60 turns, wound turn to turn. Coil L2 is wound on a ceramic frame D-50 mm and contains 70 turns of PEL wire with a diameter of 1.2-1.5 mm (winding - turn to turn). Anode choke L3 is wound on a ceramic frame D-12 mm. The original recommendation states that it contains 7 sections of 120 turns of PEL-0.4 wire wound in bulk, but most likely two sections of 120 turns are sufficient.
prefix "Sharmanka-9"
