The main selection element is a four-section quartz filter on identical resonators at a frequency of 9050 kHz, this frequency is intermediate.
The schematic diagram of the high-frequency unit is shown in Figure 1. The signal from the antenna through capacitor C1 enters the input circuit, which consists of one universal coil with taps, common to all ranges and loop capacitors C2 and C3.1. The receiver uses a variable air dielectric capacitor from a broadcast receiver, and its capacitance overlap is greater than necessary.
To reduce overlap and, as a result, increase tuning accuracy, a constant C2 is connected in series with the variable capacitor. In either case, the input circuit consists of part of the loop coil L1 and these two capacitors. In the range of 160 m (1.8 MHz), as the lowest frequency, to reduce the tuning frequency of the circuit, capacitor C4 is used, which is connected in parallel with circuit C3.1 C2.
Smooth change in tuning frequency using a variable capacitor, stepwise, when switching ranges - using switch S1 (its section S1.1).
The receiver does not have an input RF amplifier, and uses a passive mixer based on field-effect transistors VT1 VT2, to which the input circuit is connected directly, without transition capacitors or coupling coils. A significant advantage of such a mixer over diode ones is that it provides a sufficiently high transmission coefficient, so much so that there is no need for an input amplifier.
In addition, the use of field-effect transistors, characterized by good linearity, made it possible to reduce the noise level and significantly expand the dynamic range, which is most important in communications technology.
To further reduce the noise level and increase the transmission coefficient, a bias voltage is created at the gates of the field-effect transistors, the value of which, during the setup process, can be set by trimming resistor R1. Thanks to the use of a parametric stabilizer on R9 VD1, the potential of the common wire point of the converter increases, and the bias voltage turns out to be negative relative to the common wire and the input and output circuits.
Winding 3 of phase transformer T1 receives local oscillator voltage from the GPA, consisting of a master oscillator on transistors VT3 VT4 and a buffer stage on transistor VT5, which matches the high output resistance of the local oscillator circuit and the low input resistance of the transformer.
The local oscillator frequency is determined by a circuit that consists of a universal coil L2 with taps switched by the range switch section and a set of pairs of capacitors switched by section S1.3. Smooth adjustment is made using the second section of the variable capacitor C3.2, stepwise using two sections of the switch S1.2 and S1.3.
Figure 2
The schematic diagram of the IFF circuit is shown in Figure 2. It is built on bipolar transistors. There are two stages of the amplifier in total, both are made according to a cascade scheme.
The IF signal from the output circuit of the mixer is supplied to the input of the first stage of the IF at VT1 and VT2. Its collector circuit includes circuit L1C3, tuned to an IF frequency of 9050 kHz.
Through the coupling coil, the IF signal is fed to a four-section quartz filter on resonators Q1-Q4. The filter passband is adjusted using a small-sized electromagnetic relay, when the SP1 contacts are closed, the passband is reduced from 2.4 kHz to 0.8 kHz. From the output of the filter, the signal goes to the second stage of the amplifier using transistors VT3 VT4, which is made according to the same circuit.
The AGC system regulates the supply voltage of the entire amplifier, and accordingly controls its gain. The IF signal from the output of the second stage is supplied to the rectifier at VD1 VD2. As a result, a voltage appears at the base of VT8, which increases the higher the signal level. And as this voltage increases, VT8 begins to open. Which leads to a decrease in the DC voltage based on the regulating transistor VT7.
As a result, it begins to close, and the supply voltage of the entire amplifier decreases accordingly (both stages of the amplifier are powered by the emitter voltage VT7). The signal level can be judged by the IP1 indicator, which shows the actual supply voltage of the amplifier.
The demodulator is made using a field-effect transistor VT6. It is a switch that periodically interrupts the IF signal at the frequency of the reference oscillator. The input and output impedances of the demodulator are equal, however, there is no difference between its input and output.
The demodulated signal is supplied through the volume control R17 to a two-stage ultrasonic sounder using transistors VT9-VT11. The amplifier can work with any phones, but dynamic 8-40 ohms are preferable.
The reference oscillator is made using a VT5 transistor. Its frequency is stabilized by the same quartz resonator as used in the quartz filter, but its resonant frequency is shifted using capacitors C15 and C16.
Structurally, the receiver is mounted on two printed circuit boards made of single-sided fiberglass. To switch the ranges, a ceramic biscuit switch is used; it is located in close proximity to the high-frequency block board, near the heterodyne and input coils, which in turn are located mutually perpendicular. Capacitors C9-C31 are mounted directly on the contacts of this switch.
The coils of the heterodyne and input circuits are wound on cylindrical ceramic frames with a diameter of 8 mm. Winding is carried out in accordance with Figure 6.
The inverter coils are wound on frames with a diameter of 5 mm with tuning cores with a diameter of 2.0 mm made of 100 NN ferrite. After winding and installation on the board, the frames are covered with aluminum screens, which are connected to a common wire. Coils L3 and L4 of the high-frequency unit are wound on one frame; they contain 30 and 10 turns, respectively, PEV wires 0.12.
Coils L1 L3 and L5 of the IF amplifier contain 25 turns, and L2 and L4 10 turns of the same wire. The setting indicator is any microammeter for 100-150 µA. The operating modes of the high-frequency unit are shown in the diagram; for the IF path - in the absence of an input signal, the voltage on the collector VT2 and VT3 should be 1.5 V each (set by selecting R2 and R5).
Figure 4 and 5
The voltage at the emitter VT7 is 6.5V - by selecting R16. The IF path is tuned in the traditional way using a 9.05 MHz generator. Coil L5 is adjusted in such a way as to provide the highest quality sound (the frequency should be on the left slope of the frequency response of the quartz filter).
When setting up the GPA, you need to adjust the capacitors in such a way as to ensure the following frequency overlap at the GPA output:
for range 29 MHz - 19.95-20.45 MHz,
for range 28.5 MHz - 19.45-19.95 MHz,
for range 28 MHz - 18.95-19.45 MHz,
for range 24 MHz - 15.84-15.94 MHz,
for range 21 MHz - 11 95-12.4 MHz
for range 18 MHz - 9.02-9.12 MHz,
for range 14 MHz - 4.95-5.3 MP4,
for range 10 MHz - 19.15-19.2 MHz,
for range 7 MHz - 16.05-16.15 MHz,
for range 3.5 MHz - 12.55-10.1 MHz,
for range 1.8 MHz - 10.88-10.1 MHz.
Figure 6
At the first stage, a beginning shortwave radio amateur needs a HF radio receiver, with which he can observe the work of other radio amateurs. It is desirable that this be a very simple device, made on the most affordable element base, easy to set up, but providing good performance.
The receiver described in this article is just one of these. It is made according to a very simple scheme on the most affordable element base today. The receiver is built using a direct conversion circuit. It receives telegraph and telephone amateur radio stations (CW and SSB).
The receiver, in principle, can operate in any of the amateur radio HF bands - it all depends on the parameters of the input and heterodyne circuit. The article provides data on these contours for the 160M, 80M and 40M bands. The receiver was not tested on other bands.
Schematic diagram of the receiver
The sensitivity of the receiver is about 8 mkV; it works with an unmatched antenna, which is a piece of mounting wire stretched diagonally across the room under the ceiling. The role of grounding is performed by the pipe of the water supply or heating system of the house. A contact is attached to the pipe using a metal clamp, the wire from this contact is connected to terminal X4, and the antenna lowering is connected to X1.
The circuit diagram is shown in Figure 1. The input signal is isolated by the L1-C1 circuit, which is tuned to the middle of the received range. Next, the signal goes to a mixer made of two diode-connected transistors VT1 and VT2, connected back-to-back.
The local oscillator voltage is supplied to the mixer through capacitor C2 from the local oscillator made on transistor /T5. The local oscillator operates at a frequency two times lower than the frequency of the input signal.
Fig.1. Schematic diagram of a HF receiver using five KT315 transistors.
At the output of the mixer, at connection point C2, a transformation product is formed - a signal of the difference between the input frequency and the doubled frequency of the local oscillator. Since the frequency of this signal should not be more than 3 kHz, after the mixer a low-pass filter is turned on on inductor L2 and capacitor C3, suppressing signals with frequencies above 3 kHz.
Thanks to this, high receiver selectivity and the ability to receive CW and SSB are achieved. AM and FM signals are practically not received, but this is not necessary, since in the amateur bands CW and SSB are mainly used.
The selected low-frequency signal is fed to a two-stage low-frequency amplifier on VT3 and VT4, at the output of which high-impedance electromagnetic head phones of the "TON-2" type are switched on. Low-impedance dynamic telephones can only be connected through a transition transformer, for example, from a single-program radio broadcast point.
If you connect a resistor with a resistance of 1-2 kOhm 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 with a speaker and volume control. Then loudspeaker listening will be possible. The local oscillator supply voltage is stabilized by a zener diode VD1.
Details and design
The receiver can use different variable capacitors, for example, with a capacitance adjustment of 10-495 pF, 5-240 pF or 7-180 pF. It is desirable that these are capacitors with an air dielectric, but it is also possible with a solid one.
For winding contour coils, frames with a diameter of 8 mm with threaded trimming cores made of carbonyl iron are used. The frames for the frames are the frames of the IF circuits of old tube or tube-semiconductor TVs (ULT, CNT, ULPPT, etc.). The frames are disassembled, unwound and a cylindrical part of 30 mm in length is sawed off.
The frames are installed into holes in the receiver's printed circuit board and secured there with thick epoxy glue and glue. A schematic representation of the frame with a coil and the method of its attachment is shown in Figure 2.
Fig.2. Designs and fastening of coils.
The same figure shows the method of attaching the L2 coil, made on a ferrite ring. This coil is also attached through a hole in the board, but using an M3 screw with a nut, which is inserted into the hole in the ring. An insulating washer is placed under the screw.
Fig.3. Printed circuit board of the HF receiver using Kt315 transistors.
Rice. 4. Location of parts on the HF receiver board.
Now the winding data. As noted above, winding data is given for three ranges (see table). In addition to winding data, data for capacitances C1, C9, C8 is also given for three ranges.
In addition, the capacitance C8 is given for different variable capacitors. If the variable capacitor at your disposal is not of the same capacity as indicated in the table (10-495, 5-240 or 7-180), then select the data according to the closest maximum capacity. For example, if there is a capacitor of 7-270 pF, then take the capacitance data for a variable capacitor of 5-240 pF.
The coils L1 and L3 are wound turn to turn using PEV 0.12 wire. The windings are fixed with drops of molten paraffin (from a candle).
Coil L2 - wound on a ferrite ring with a diameter of 10-20 mm, it contains 200 turns, wound in bulk, but evenly. Coil L2 can also be wound on another core, for example, on SB. In this case, it is wound on the SB frame and then placed inside the SB armor cups. The cups are glued with epoxy glue, which is also used to glue the coil to the board.
Capacitors C1, C8, C9, C11, C12, C13 must be ceramic, tubular or disk. If these are imported disk capacitors, then you need to know how their capacitance is indicated - the first two digits indicate the capacitance, and the third - the multiplier. The multiplier is indicated by the numbers 1, 2, 3, 4.
If 1 = x10, 2 = x100, 3 = x1000, 4 = x10000.
For example, "47" - 47 pf, "471" - 470 pf, "472" -4700 pf, "473" - 47000 pf (0.047t), "474" - 0.47m.
The printed circuit board is made of foil fiberglass. The location of the printed tracks is on one side only. The track pattern and wiring diagram are shown in Figures 3 and 4.
Setting up
The low-frequency amplifier of the receiver, with error-free installation and serviceable parts, works immediately after the first turn on. The operating modes of transistors VT3-VT4 are set automatically, so that setting up the ULF is not required. Therefore, basically, setting up a receiver consists of setting up a 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). 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; on the 160 M range, the local oscillator frequency should be adjusted within 0.9-0.99 MHz, on the 80 M range - 1.7-1.85 MHz, on the 40 M range - 3.5 -3.6 MHz. The easiest way to do this is by measuring 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 (for example, place the wire connected to X1 next to the generator output cable).
The HF generator needs to be tuned within frequencies twice as high as those indicated above (for example, in the 160M range - 1.8-1.98 MHz), and the local oscillator circuit must be adjusted so that with the appropriate position of the SY in phones, sound with a frequency of about 0 is heard .5-1 kHz. Then, tune the generator to the central frequency of the range, tune the receiver to it and adjust the L1-C1 circuit to the maximum sensitivity of the receiver. Using the same generator, calibrate the receiver scale.
You can also calibrate the receiver scale using a frequency meter, measuring the frequency at tap L3 and multiplying the frequency meter readings by 2. In the absence of an RF generator, the input circuit can be adjusted by receiving a signal from an amateur radio station operating closer to the middle of the range.
In the process of setting up the circuits, it may be necessary to slightly adjust the number of turns of coils L1 and L3 or capacitors C1 and C9.
A shortwave receiver, as we know, “the theater begins with a hanger,” and the path to shortwave begins with listening to amateur bands and observing the operation of amateur radio stations. On short waves, radio amateurs conduct radio communications in the ranges of 160 m (1.81-2.0 MHz), 80 m (3.5-3.8 MHz), 40 m (7.0-7.2 MHz), 30 m ( 10.1-10.15 MHz), 20 m (14.0-14.35 MHz), 17 m (18.068-18.168 MHz), 15 m (21.0-21.45 MHz), 12 m (24. 89-24.99 MHz) and 10 m (28.0-29.7 MHz).
As a rule, the main problem of a beginning shortwave operator is a receiver on the amateur bands, or rather, the lack thereof. Commercially produced HF survey receivers are quite expensive; in addition, almost all models are mainly focused on receiving signals from broadcast radio stations operating in amplitude modulation mode, and do not provide good reception of amateur radio stations using various types of radiation - telegraph (CW), single-sideband modulation with suppressed carrier (SSB) and others (for example, phase-shift keyed, used in digital types of radio communications).
A not very complex homemade HF receiver for the amateur bands can be made by a novice radio amateur, but it should be kept in mind that setting up a homemade receiver is a process that requires an understanding of the operation of both individual components and the design as a whole. Most often, when tuning, you cannot do without a minimum of measuring instruments, so it is advisable to manufacture and configure the receiver under the guidance of a fairly experienced radio amateur or radio electronics specialist.
A receiver developed by a Polish radio amateur. SP5AHT operates on the amateur bands 160, 80, 40, 20, 15 and 10 m and fully meets the requirements for beginner designs. The receiver circuit is quite simple, and the proposed original design makes it easier to replicate the device. The choice of only 6 amateur HF bands was dictated by the number of positions of the small-sized flip switch used. Instead of one or more of the indicated ranges, you can enter others - for example, replace the 10 m range with a 17 m range. The receiver supply voltage is 12-14 V, the current consumption is no more than 50 mA.
The receiver is a superheterodyne with an intermediate frequency of 5 MHz, at which the main selection of received signals is carried out. The main selection filter is quartz, made on 4 small-sized quartz resonators with a frequency of 5 MHz.
The receiver circuit is shown in Fig. An antenna is connected to the receiver via connector XS1. The signals received by the antenna are sent to variable resistor R1, which is used to adjust the volume. Next, through the isolation capacitor C12, the signals are supplied to the input circuit formed by the capacitor C13 and one of the coils L1-L6, selected by a roller switch. The small capacitance of capacitor C12 (10 pF) slightly degrades the quality factor of the input circuit.
In the switch position shown in the diagram, the circuit is formed by capacitor C13 and coil L1. The 1st gate of the field-effect transistor T1 is connected to this circuit, which is a mixer for the received signals and the local oscillator signal supplied to the 2nd gate of the transistor through the isolation capacitor C14.
The local oscillator is made on transistor T2 and, to increase the stability of the generated frequency, is powered by an integrated 9-volt stabilizer. The local oscillator circuit is formed by coil L7 and capacitor C10. the capacitance of the varicap D1 and one of the capacitors C1-C6, selected by a biscuits switch. In the switch position shown in the diagram, capacitor C6 is connected to the circuit.
The tuning of the local oscillator in frequency, and therefore tuning to the received radio station, is carried out by changing the capacitance of the varicap D1, to which voltage is supplied from the variable resistor R1. For ease of adjustment, a plastic handle is placed on the axis of this resistor. Via the XS2 connector, you can connect a digital scale to the local oscillator, the indicator of which will display the receiver’s tuning frequency.
In superheterodyne reception, the intermediate frequency is the sum or difference of the frequencies of the received signal and the local oscillator signal. This receiver uses an intermediate frequency of 5 MHz, so when operating in the 160 m range, the local oscillator frequency should vary from 6.81 to 7.0 MHz (5 + (1.81-2.0)).
Local oscillator frequencies for all amateur HF bands (for an intermediate frequency of 5 MHz) are given in Table 1. 
It should be borne in mind that the selected local oscillator circuit is a compromise. On some bands the frequency overlap will be “with a margin”. On others, it will not be possible to completely cover the entire range (in particular, in the 10 m range). There is no need to strive for full range coverage. With wide frequency overlap, the tuning density (the number of kilohertz per turn of the tuning knob) increases significantly, and tuning to the radio station becomes very “sharp”. In addition, the uneven pressure of the slider to the conductive layer that occurs in each variable resistor becomes more noticeable. Which can lead to abrupt changes in frequency. Thus, when tuning the receiver, it is advisable to use capacitors C1-C6 to set the local oscillator frequencies to the most popular sections of the ranges. Which in this scheme do not completely overlap.
A signal with an intermediate frequency of 5 MHz, generated at the mixer output, passes through a 4-crystal quartz filter. The filter bandwidth is about 2.4 kHz. Resistors R8 and R10 are a matched load at the input and output of the filter and prevent deterioration of its amplitude-frequency characteristics due to the influence of receiver stages.
The signal isolated by the quartz filter is fed to the 1st gate of transistor T4, which plays the role of a mixing detector. The 2nd gate of the transistor receives a signal from the reference quartz oscillator on the TZ transistor. Using coil L8, the generator frequency is set to the corresponding frequency of the lower slope of the quartz filter. In this case, at the selected local oscillator frequencies (Table 1), stations emitting single-sideband signals with lower sideband (LSB) will be received in the ranges of 80 and 40 m, and in the ranges of 20, 15 and 10 m - with upper sideband (USB).
At the output of the mixing detector, a low-frequency signal is generated (i.e., corresponding to the speech of a radio operator or the tone of telegraph messages), which first passes through a low-pass filter C27-R13-C30. “Cuts off” the high-frequency components of the spectrum, and then is fed to the input of a low-frequency amplifier using transistors T5-T7. The first stage of the amplifier, made on transistor T5, through capacitor C31 is covered by negative AC feedback, which limits the gain at frequencies above 3 kHz. Narrowing the amplifier's bandwidth makes it possible to reduce the noise level. The second and third stages on transistors T6 and T7 are galvanically coupled. The load of the third stage is low-impedance headphones.
In the author's design, the L7 coil is wound on a T37-2 ring (red) with a 00.35 mm wire and contains 20 turns with a tap from the 5th turn, counting from the pin connected to the common wire. The inductance of coil L7 is 1.6 μH. If a coil on a cylindrical frame is used, it must be placed in the screen.
It is advisable to wind the L1 coil, which is used in the input circuit in the 160 m range, on a ferrite (for example, 50HF) or carbonyl ring (for example, T50-1). The remaining coils (L1-L5, L8) are standard small-sized chokes. The inductance of coils L1-L6 is given in Table 2, the inductance of L8 is 10 μH.
In the ranges of 10 and 15 m, the inductances of the coils L5 and L6 are quite small, which is explained by the large capacitance of the loop capacitor C13, which was chosen based on a compromise - to ensure satisfactory parameters of the input circuit on most amateur bands. The low equivalent circuit resistance in the 10 and 15 m ranges leads to a significant decrease in the sensitivity of the receiver, so it is advisable to abandon the use of the receiver in the 10 m range, replacing it with the 17 m range, for which the inductance of the input circuit coil should be 0.68 μH.
Trimmer capacitors - C1-C6 - small-sized, for printed circuit mounting, with a maximum capacitance of up to 30 pF. When tuning the local oscillator on some ranges, capacitors of constant capacitance are soldered in parallel with the tuning capacitors SZ-S6 - for example, in the range of 160 m - 300 pF, in the range of 80 and 20 m - 200 pF, in the range of 40 m - 100 pF.
It is advisable to use multi-turn variable resistor R1. BF966 transistors can be replaced with KP350, but then you will have to install resistor voltage dividers (100 k/47 k) in the gates. Instead of the BF245 transistor, you can use KP307, which may have to be selected from several copies in order for the local oscillator to operate stably on all ranges. BC547 transistors are replaced with KT316 or KT368 (in the reference oscillator) and with KT3102 in the low-frequency amplifier. The receiver parts are installed on a printed circuit board (Fig. 2).
Installation of parts is carried out on supporting “spots” cut out in foil. The rest of the foil is used as a “common wire”.
Other types of biscuit switches (for example, PKG type) can be used in the receiver. But then you will have to slightly change the arrangement of elements on the printed circuit board and its dimensions.
It is most advisable to configure the receiver components as the radio elements are installed. Having installed the low-frequency amplifier parts on the board, check the installation for compliance schematic diagram and supply voltage. The constant voltage on the collectors of transistors T5 and T6 (Fig. 1) should be about 6 V. If the voltage deviates significantly from the specified one, the required operating mode of the transistors is established by selecting the resistances of resistors R16 and R17. When you touch the upper (according to the diagram) terminal of resistor R16 with a screwdriver in headphones connected to the amplifier output, a strong hum should be heard. The operation of the reference oscillator on the TZ transistor is checked using a frequency meter by connecting it to the upper (according to the diagram) terminal of capacitor C25. The generator output frequency should be around 5 MHz and remain stable.
The operation of the local oscillator on transistor T2 is also checked using a frequency meter connected to connector XS2. The local oscillator must operate stably on all ranges. And “setting” frequencies within the required limits (Table 1) should be done by adjusting the capacitances of trimming capacitors C1-C6. Rotate the adjustment knob from one extreme position to the other. If necessary, constant capacitors are installed in parallel with the tuning capacitor.
At the final stage of tuning, a signal from a standard signal generator is supplied to the antenna input of the receiver on each band. And they check the sensitivity of the receiver by range. A significant deterioration in sensitivity on one or more ranges can be caused by insufficient amplitude of the local oscillator signal (selection of transistor T2 will be required). Detuning of the input circuit (it is necessary to check the compliance of the inductance of the coils with the data in Table 2) or a very low quality factor of the coil. For which a standard small-sized inductor is used (the inductor will need to be replaced, for example, with a coil wound on a ferrite ring).
If the sensitivity of the shortwave receiver.
It will be quite sufficient for working in the ranges of 160-20 m (3-10 µV). But signals from amateur radio stations on any range are received with distortion, most likely. It is necessary to more accurately set the frequency of the reference quartz oscillator by selecting the inductance of coil L8.
Given the low sensitivity of the receiver, for successful observations of the operation of amateur radio stations, an external antenna should be used.
Simple Observer Receiver
The topic of a simple observer receiver for beginners haunts many, and far from beginning, radio amateurs.... Designs are periodically published, new “threads” are opened in forums, etc.... So from time to time I think about this topic.... I still want to find the solution that is optimal in terms of simplicity, repeatability, and availability of components....
Of course, in our time the easiest way for those who want to listen to radio broadcasts for the first time with decent quality is an SDR receiver...
But many are interested in the “classics” - a superheterodyne or PPP with a GPA and without a synthesizer.... Many beginning radio amateurs already have experience in radio engineering, but do not have experience in the field of radio reception, and, as a rule, do not have normal range antennas, but would like to try their hand at . It was for this category that I tried to “invent” a receiver...
I don’t think it’s worth making your first receiver all-band - it’s difficult to use a VFO, and with up-conversion you need a synthesizer, and making it single-band is also not very interesting... In my opinion, a compromise in the form of a 3-band receiver for 80-40 is interesting -20 m (it is clear that in the proposed scheme you can make all ranges if desired), i.e. the most interesting ranges that are active at different times of the day, i.e. You can always hear something, which is interesting for a beginner.
The receiver, despite its simplicity, must have good dynamics and selectivity in the mirror channel - otherwise, when receiving on various surrogate “ropes”, which beginners usually use, in addition to the whistle of “broadcasters” and noise, it will be difficult to receive anything - and the attenuator will not always help .
Regarding the structure...I thought through many options....And still returned to the proposed one - a superheterodyne with a quartz filter.... If there is an EMF available, then it might make sense to do a double conversion, but if there is no EMF? In my opinion, it’s easier to purchase 5 quartz crystals for one frequency and make a 4-crystal filter, which is quite suitable for a receiver of this class.
Regarding the components... There are also a lot of disagreements - for some the 174XA2 is already “exotic”, but for others it is affordable, etc. Therefore, I came to the conclusion that there should be no microcircuits in the radio path... And the parameters can be obtained better and there will be fewer problems with the search - transistors are always easier to find.
GPA.... Critical unit... I think you need to do electronic adjustment on varicaps - KPIs and verniers are a problem for many... Even without a multi-turn resistor, you can get by with the usual two and make rough and smooth adjustments separately.
DFT - at least 2-path...
It is clear that most radio amateurs are “scared off” from building a receiver by the need to wind the coils, not always available winding data, problems finding frames like the author of a particular circuit, etc. I also thought about how to “unify” the coils and decided that it was best to use “Amidon” rings, which are becoming more and more accessible and have excellent and easily calculated parameters.... The repeatability of designs with such rings is also excellent - an example is Softrock and many other sets... It is very convenient to calculate any filter in RFSIM and receive the inductance value to calculate the number of turns under famous brand rings according to the simplest formula The Al parameter is in the datasheet for each brand - for example, for T-25-2 it is equal to 34, that is, with 100 turns we get 34 μH
I also think that trimming capacitors are not a problem - “imported” TSC-6 ones are excellent, which are installed in almost all radio receivers...
Receiver circuit
The quartz filter of the receiver provides the ability to smoothly adjust the band, and if this is not necessary (or there are simply no varicaps available), simply replace the varicaps with capacitors with a capacity of 82 - 120 pF to obtain the desired bandwidth of 2.4 - 3 kHz.
There will be no problems with a cascode amplifier - you just need to select the optimal operating mode using the trimmer R19 and R17... You can introduce IF gain control by replacing R19 with a variable resistor.
Instead of the IF circuit L1, we will use a standard DM-01 inductor (or a similar one) of 1 μH.
Problem with DFT? We take any available frames (from the same soap dish) and make... The inductance is known... Or the internal insulation of the cable (you can use frames from medical syringes). We calculate the required number of turns and wind.... There are many methods for calculating the number of turns of coils. Another option is to take DM-01 chokes for 1 μH and set the DFT to 20 m.... There is no problem recalculating the DFT for all ranges for standard inductances...
The filter is made of PAL resonators with a frequency of 8.867 MHz
The frequency spread accuracy is desirable up to 200 Hz.
On replacing transistors.
Transistors KP302, 303, 307, DF245, etc. are used in the mixer. The modes are selected by a resistor at the source.
We will replace VT2 with KT368 or any high-frequency low-noise one.
V ULF - KT3102E
Receiver PCB
Receiver improvement.
As a result of the tests, it turned out that there is enough sensitivity in the low frequency ranges, but not enough in the high frequency ranges. Therefore, the mixer was slightly modified.
Modified receiver circuit
Homemade HF (short wave) receivers are made on the basis of resistor switches. Many modifications include a wired adapter and are equipped with amplifiers. The standard circuit has high frequency stabilizers. To adjust the channels, knobs with pads are used.
It should also be noted that receivers differ from each other in conductivity and frequency of tetrodes. In order to understand this issue in detail, it is necessary to consider the circuits of the most popular receivers.
Low frequency devices
The circuit of a homemade HF receiver includes a controlled modulator, as well as a set of capacitors. Resistors for the device are selected at 4 pF. Many models have contact triodes that operate from converters. It should also be noted that the receiver circuit includes only single-pole transceivers.
To adjust the channels, regulators are used, which are installed at the beginning of the chain. Some models are made with only one adapter, and the connector for them is selected as a linear type. If we consider simple models, they use a grid amplifier. It operates at 400 MHz. Isolators are installed behind the modulators.
High frequency tube models
Homemade tube HF high-frequency receivers include contact transducers and low-conductivity sensors. Some experts speak positively about these devices. First of all, they note the ability to connect transceivers. Triggers for modification are suitable for the controller type. The most common devices are those with semiconductor resistors.
If we consider the standard circuit, then the comparator is of an adjustable type. Output resistors are installed with a capacity of at least 3.4 pF. Conductivity does not fall below 5 microns. The controls are installed on three or four channels. Most receivers use only one phase filter.
Pulse modifications
A homemade pulse HF receiver for amateur bands is capable of operating at a frequency of 300 MHz. Most models fold with contact stabilizers. In some cases, transceivers are used. The increase in sensitivity depends on the conductivity of the resistors. the output is 3 pF.
The average conductivity of contactors is 6 microns. Most receivers are manufactured with dipole adapters that accept PP connectors. Very often there are capacitor blocks that operate from thyristors. If we consider lamp models, it is important to note that they use single-junction comparators. They turn on only at 300 MHz. It should also be said that there are models with triodes.
Single pole devices
Single-pole homemade HF tube receivers are easy to set up. The model is assembled with your own hands with variable comparators. Most modifications are designed with low conductivity stabilizers. The standard one involves the use of dipole resistors with an output capacitance of 4.5 pF. Conductivity can reach up to 50 microns.
If you assemble the modification yourself, then the comparator must be prepared with a transceiver. Resistors are soldered onto the modulator. The resistance of the elements, as a rule, does not exceed 45 Ohms, but there are exceptions. If we talk about relay receivers, they use adjustable triodes. These elements operate from a modulator, and they differ in sensitivity.
Assembly of multi-pole receivers
What are the advantages of a multi-pole HF detector receiver for the amateur bands? If you believe the reviews of experts, these devices produce a high frequency and at the same time consume little electricity. Most modifications are assembled with dipole contactors, and adapters are used of the wired type. Connectors for devices are suitable for different classes.
Some models contain phase filters that reduce the risk of interference from wave interference. It should also be noted that the standard receiver circuit involves the use of a regulator to adjust the frequency. Some instances have comparators of the channel type. In this case, the triode is used with only one insulator, and its conductivity does not fall below 45 microns. If we consider expander receivers, they are only capable of operating at low frequencies.
Models with two-junction converter
HF receivers for amateur bands with two-junction converters are capable of stably maintaining a frequency of 400 MHz. Many models use a pole zener diode. It is powered by a converter and has high conductivity. The standard modification circuit includes a controller with three outputs and a capacitor. The amplifier for the model is suitable with a varicap.
It should also be noted that high-frequency devices with a converter of this type can cope perfectly with impulse noise from the unit. Comparators are used with grid and capacitive resistors. The resistance parameter at the input of the circuit is about 45 Ohms. In this case, the sensitivity of receivers can vary greatly.
Devices with three-wire converter
A homemade HF receiver for amateur bands with a three-wire converter has one contactor. The connectors can be used with or without a cover. It should also be noted that resistors are used of different conductivities. At the beginning of the circuit there is a 3 micron element. As a rule, it is used as a single-pole type and allows current to flow in only one direction. The capacitor behind it is located with a linear conductor.
It should also be noted that the resistors at the output of the circuit have low conductivity. Many receivers use them as an alternating type and are capable of passing current in both directions. If we consider modifications at 340 MHz, then in them you can find comparators with grid triodes. They operate at high resistance, and the voltage is as much as 24 V.
200 MHz modifications
A homemade HF receiver for the amateur bands with a frequency of 200 MHz is very common. First of all, it should be noted that the models are not able to work on comparators. Linear modifications are common. However, the most common devices are considered to be models with transition decoders. They are installed with a set of adapters. Resistors at the beginning of the circuit are used with high capacitance, and their resistance is at least 55 Ohms.
Amplifiers are available with and without filters. If we consider switched modifications, they use duplex capacitors. In this case, the stabilizer is used with a regulator. A modulator is required to configure channels. Some receivers work with receivers. They have a PP series connector.
300 MHz devices
A homemade HF receiver for amateur bands with a frequency of 300 MHz includes two pairs of resistors. Comparators in models have a conductivity of 40 microns. Some modifications contain wired extenders. These elements can significantly relieve the load on capacitors.
If you believe the reviews of experts, then models of this type are distinguished by increased sensitivity. Homemade devices are produced without tetrodes. To improve signal conductivity, only transistors are used. It should also be noted that there are devices with channel filters.
Modifications at 400 MHz
The 400 MHz device circuit involves the use of a dipole adapter and a network of resistors. The model's transceiver is used with an open filter. To assemble the device with your own hands, first of all, a tetrode is prepared. Capacitors for it are selected with low conductivity and sensitivity at the level of 5 mV. It should also be noted that receivers with low-frequency type converters are considered common devices. Next, to assemble the device with your own hands, take one modulator. This element is installed in front of the converter.
Low sensitivity tube devices
A tube HF receiver for low-sensitivity amateur bands is capable of operating on different channels. The standard design of the device involves the use of one stabilizer. In this case, the adapter is used as an open type. The conductivity of the resistor must be at least 55 microns. It is also important to note that receivers are manufactured with covers. To assemble the device with your own hands, a set of capacitors is prepared. Their capacitance must be at least 45 pF. It is especially important to note that receivers of this type are distinguished by the presence of duplex adapters.
High sensitivity receivers
The high sensitivity device operates at 300 MHz. If we consider a simple model, it is assembled on the basis of a comparator with a conductivity of 4 microns. In this case, filters under it can be used with a lining.
Transistors on the receiver are installed of the unijunction type, and filters are used at 4 pF. Wired transceivers are quite common. They have good conductivity and do not require large energy consumption.
The modulator may only be used with one varicap. Thus, the model is able to work on different channels. To solve problems with negative resistance, an expansion capacitor is used.