In Fig. Figure 1 shows a schematic diagram of a fairly simple converter made using a single 6I1P lamp. With a similar converter on a receiver that has only the MF and DV bands (“Volna”, “Ogonyok”, “Strela”, “Serenade”, etc.), it is possible to receive “with extended tuning” short-wave broadcast radio stations that operate in the following areas:

1. 25 m (11.6 - 12.1 MHz);
2. 31 m (9.4 - 9.9 MHz);
3. 41 m (7.1 - 7.6 MHz);
4. 49 m (5.8-6.3 MHz).

In this case, the converter with the receiver operates as a superheterodyne with double frequency conversion, whose second intermediate frequency is variable. Smooth tuning to the received radio station is carried out by a block of variable capacitors in the receiver.

First converter circuit

As can be seen from the diagram, the signal of the received radio station from antenna An through section B1a of switch B1 and separating capacitor C17 is supplied to antenna coil L1, to which the input circuit formed by coil L2 and capacitors C1, C9 is inductively coupled; C2, C10; NW, C11; C4, C12.

With these capacitors, the input circuit is tuned to the average frequency of the corresponding range, i.e., to a frequency of 11.85; 9.65; 7.35; 6.05 MHz. An abrupt change in the tuning frequency of the input circuit is carried out by the B1v switch section.

The local oscillator circuit consists of inductor L3 and capacitors C5, C13; C6, C14; C7, C15; C8, C16, which are connected by the V/G switch section. Feedback coil L4, inductively coupled to coil L3, is connected to the anode circuit of the triode part of the lamp.

Switch sections B1a, B1b and toggle switch B2 paired with the switch are used to switch to operation of the receiver without a converter. When switch B1 is set to any of the bands, the antenna is connected to the input of the converter (B1a), the lamp is supplied with filament voltage (B2), and the output of the converter is connected to the input of the receiver through capacitor C22 and section B16;

Rice. 1-2. Schematic diagrams of tube converters for the HF range.

The converter part of the converter is assembled according to the usual scheme. The voltage of the received signal is supplied to the control grid 2 of the heptode part of the lamp, and the local oscillator to the third (9).

As a result of frequency conversion, a component of the difference (intermediate) frequency is released on resistor R2, which, as mentioned above, is supplied to the input of the receiver. In this converter, the local oscillator frequency when operating at 25, 31, 41 and 49 g is selected higher than the average frequency of the range at 1250 kHz and, accordingly, is equal to 13.1; 10.9; 8.6 and 7.3 MHz.

The converter uses standard parts: switch B1 - flat, two-board with 5 positions and 4 directions; toggle switch B2 type TV2-1. Permanent capacitors type KSO-1, MBM, KT. Trimmer capacitors C1-C8 type KPK-1 or homemade.

To make homemade tuning capacitors from PEL 1.5 wire, cut 8 rods 35-40 mm long. One end of the rod is cleaned (8 mm) and tinned. Then 75-80 turns of PEL 0.15 wire are wound tightly around the rod (Fig. 2), turn to turn. The turns of the wire will be the second plate of the capacitor, and the first will be the rod itself.

Inductors L1 - L4 are homemade. They are wound on polystyrene or textolite frames. You can use ribbed frames of the HF ranges from receivers “Mir”, “Baltika”, “Zvezda”, etc. The diameter of the frames is 18-20, height 30-32 mm. Coil L1 contains 21 turns of PELSHO 0.15 wire.

Winding is ordinary, two-layer, at a distance of 2 mm from coil L2. The latter contains 16 turns of PEL wire 0.64, single-layer winding.

Local oscillator coils are wound on another frame: L3 contains 14 turns of PEL 0.64 wire; L4 - 9 turns of PELSHO 0.15 wire. About four turns of coil L4 are wound between the turns of coil L3, and the rest are wound 2 mm away from it. The winding length of coils L2, L3 is 25 and 27 mm, respectively.

Setting up the converter begins with checking the presence of voltage on the electrodes of lamp L1 and the operability of the local oscillator on all ranges. If the local oscillator is working, then when coil L3 is closed, the voltage on capacitor C23 should decrease.

Then switch VI is set to the “25 G” position, the receiver is tuned to a frequency of 1.25 MHz, a modulated signal with a mid-range frequency (11.85 MHz) is supplied to the converter input - socket Gni from the signal generator (SG) and tuning begins heterodyne circuit at frequency fg(25m)=fav(25zh)+1.25= 11.85+ 1.25= 13.1 MHz.

The capacitance of capacitor C13 is selected to obtain the required local oscillator frequency as follows. First, the capacitance of this capacitor is taken to be obviously less than that indicated in the diagram and a graduated variable capacitor with a maximum capacitance of the order of 300-400 pF and a minimum of 5-10 pF is connected in parallel to it. With such a capacitor, it is easy to set the desired local oscillator frequency (13.1 MHz).

Since in this case, a signal with a modulation frequency will be heard at the output of the receiver (in the loudspeaker). After this, the variable capacitor is disconnected and a permanent capacitor of the required capacity is installed instead. Precise setting of the local oscillator frequency is carried out using a tuning capacitor C5.

Having finished setting the local oscillator frequency, reduce the signal level from the SG and, at the highest volume at the receiver output, use capacitors CI, C9 to adjust the input circuit to a frequency of 11.85 MHz. The converter is configured in the same way for other ranges.

With this choice of local oscillator frequencies, the frequency spectrum of each HF range will be converted into a spectrum from 1000 to 1500 kHz, that is, into the high-frequency part of the medium wave range.

Second converter circuit

The converter, the circuit diagram of which is shown in Fig. 3, designed to operate in the range 24-75 m. In combination with a receiver having a mid-wave range, it also forms a double frequency conversion receiver.

The first intermediate frequency (1600 kHz) in this converter has a fixed value. The radio receiver is tuned to this frequency, to the input of which the converter output is connected. The receiver does not adjust during reception of an HF radio station.

The input circuit of the converter L2, C2, C3 is connected to the control grid circuit 2 of the pentode part of the lamp L1 and is connected to the antenna using the coupling coil L1. The Circuit is tuned to the signal frequency using a variable capacitor C3, included in the block of capacitors C3, C13.

The converter local oscillator is mounted on the triode part of lamp L1 according to a three-point circuit with cathode coupling. The oscillatory circuit of the local oscillator L5, C11, C12, C13 is adjusted to the required frequency with a variable capacitor C13. Capacitors C11, C12 and C2 are mating. The local oscillator frequency was selected higher than the received one by 1.6 MHz.

As can be seen from the diagram, the converter is a conventional conversion stage of a superheterodyne receiver operating in the single-grid mixer mode, since the voltage of the signal and the local oscillator (through capacitor C7) acts on the same (first) grid of the pentode part of the lamp.

As a result of the conversion process to oscillatory circuit LZ, C8, tuned to 1600 kHz, an intermediate frequency voltage is released, which is supplied to the receiver input using the coupling coil L4.

Lamp operating mode DC set with resistors R2, R3, R4 and R6. Capacitors C5, C6, C10 and C14 are blocking. When the converter is operating with a receiver, switch B1 and toggle switch B2 paired with it are set to position “K”.

Coils L1, L2 and L5 are wound on standard ribbed polystyrene frames with a diameter of 18 mm; in this case, the turns of the coils L2 and L5 are placed in the existing thread.

Coil L2 contains 15 turns, L5—4+9 turns of PEL wire 0.64. Coil L1 is placed on the same frame with coil L2 and it contains 25 turns of PELSHO 0.12 wire. Some of the turns (7-10) are located between the L2 turns, the rest - at a distance of 2-3 mm from it.

The L3 coil is wound on a cardboard frame with a diameter of 10 mm between two cheeks located at a distance of 7 mm. The L4 coil is wound on a similar but movable section located at the bottom of the frame. Coil L3 contains 100, L4 - 150 turns of PELSHO 0.12 wire. Winding is done in bulk. The distance between the coils is selected when setting up the converter. All cores are of the SCR-1 type.

Switch B1 is a biscuit type, with three positions (only two positions are used in the circuit); resistors type MLT, capacitors type KBG-I, KTK-1, KPK-1, etc. A block of variable capacitors with a maximum capacity of 490-510 pF must have a vernier device.

Setting up such a converter is no different from setting up the conversion stage of a conventional superheterodyne receiver.

By turning on the converter and connecting it to the receiver, which is pre-tuned to a frequency of 1600 kHz, check the operating mode of lamp L1.

A deviation of the measured voltages by ±20% compared to the specified values ​​does not affect the operation of the converter. Then they check the performance of the local oscillator over the entire range. If at the end of the range the oscillations break down, you need to more carefully select the location of the cathode connection to the L5 coil.

The next stage of setup - setting up the L3, C8 circuit at a frequency of 1600 kHz, setting the local oscillator frequency and pairing the settings of the input and heterodyne circuits is carried out according to the generally accepted method (see V. Bolshov “Setting up radio receivers”, “Mass Radio Library”, issue 457, ed. “ Energy", 1963).

Scheme of a simple homemade short-wave (HF) converter for receiving broadcast stations on a receiver with a CB (MW) band. Nowadays, most audio equipment is equipped with a VHF-FM (FM) receiving path. A smaller portion is AM and FM, with "AM" usually being medium wave (MW or MW).

Less commonly, there are two AM bands - NE and LW (MW and LW). And very rarely, along with NE and LW, the short-wave range (SW) is also present. But the fact of the matter is that in recent years there has been absolutely nothing to do in the NE (MW) and Far East (LW). Only at night on NE (MW) you can receive a few long-distance radio stations. At the same time, radio broadcasting on HF (SW) is not particularly reduced.

But the most interesting thing is that the specificity of the propagation of radio waves in the shortwave range is such that, thanks to multiple tropospheric reflection, it is possible to receive very long-distance radio stations on a very mediocre receiving device.

You can receive radio stations from the most different countries, at the most different languages, which is especially useful for people studying foreign languages, because by listening to the radio in the language you are learning, you can very effectively practice both pronunciation and translation.

In my opinion, it’s completely in vain that the industry pays so little attention to the short-wave range, and it’s time to release equipment with “FM / SW” bands. But nonetheless. However, converting any AM receiver or receiving path with the CB (MW) band to receiving short waves is not so difficult.

It is necessary to connect an additional frequency converter between the antenna and the antenna input, a converter that will receive HF (SW) radio stations and transfer them to the SW (MW) band, where they can then be listened to using a receiver with the SW (MW) band.

Schematic diagram

This topic has already been widely studied by radio amateurs and there are many descriptions of KB converter circuits in the literature. Without pretending to be original, I will give a diagram (Fig. 1) of a KB converter that I have been using for several years. The scheme is very simple and does not require any setup at all.

The desire to completely abandon the need for adjustment required abandoning the input circuit. This, of course, to a certain extent affected the selectivity in the mirror channel, but reception remained possible.

For example, when using a quartz resonator with a frequency of 8.86 MHz from video equipment, it becomes possible to receive in two sub-bands at once, in the lower, within 7.3-8.3 MHz, and in the upper, within 9.4-10.5 MHz, which covers the range “31 meters” and partly the “41 meters” range.

Rice. 1. Schematic diagram homemade HF converter on the SA612A chip (resistor R1 - 510 Ohm).

Details

Of course, there is a nuisance in the fact that both ranges simultaneously appear on the same scale, but, nevertheless, reception is possible and with very good quality.

Although, of course, you can install an input circuit or even two input circuits, one at “31 meters”, the other at “41 meters” and switch them. But this will require adjustment and adjustment of these circuits to these frequencies, which will significantly complicate the manufacture of such a converter at home.

Other quartz resonators can be used. It is important to know that a receiver with a CB (MW) range covers the range 0.52 - 1.6 MHz. And the broadcasting sections of the KB band are located as follows:

• 90 meters - 3.2 - 3.4 MHz.
• 75 meters - 3.9-4.0 MHz.
• 60 meters - 4.75 - 5.06 MHz.
• 49 meters - 5.9-6.2 MHz.
• 41 meters - 7.1 - 7.4 MHz.
• 31 meters - 9.5 - 9.9 MHz.
• 25 meters - 11.65 - 12.06 MHz.
• 22 meters - 13.6 -13.8 MHz.
• 19 meters - 15.1 -15.6 MHz.
• 16 meters - 17.55 -17.9 MHz.
• 13 meters - 21.45 - 21.85 MHz.
• 11 meters - 25.65-26.1 MHz.

To understand what range will be accepted when using a specific quartz resonator, you need to add or subtract the frequency of the MF (MW) range from its resonant frequency. That is, to determine the lower limit, add (subtract) 0.52 MHz, and to determine the upper limit, add (subtract) 1.6 MHz.

Installation

The converter was installed on printed circuit board, shown in Fig. 2.

Rice. 2. Printed circuit board for the HF converter on the SA612A chip.

Nowadays, high-quality broadcasting on VHF-FM or FM bands is most widespread. Even in the outback there can be up to a dozen radio stations on these bands. At the same time, perhaps in order to save resources, the number of local radio stations operating on the MW and LW (MW, LW) bands is being reduced. In some cities and even regional centers there is no longer a single local radio station operating on these bands, and if there is at least one, then it is duplicated on one of the VHF FM bands.

As a result, the MF and DV bands, which are available in most radios and radio tape recorders, are not used, since there are almost no local radio stations operating on these bands, and long-distance reception on them is possible only at night and with a low level of interference.

At the same time, radio broadcasting on short waves is not reduced, and the specifics of KB distribution make it possible to receive a large number of remote radio stations, mainly foreign, both day and night. In this regard, it makes sense to replace the unused MF or LW range with a short-wave range. The easiest way to do this is with a simple converter, the diagram of which is shown in the figure.

The converter is a frequency converter made according to a circuit with a combined local oscillator. The role of local oscillator and mixer falls on a single stage on VT1. The local oscillator frequency is stabilized by the most common quartz resonator on sale today at 8.86 MHz (from PAL TV decoders).

The input jack of the WS1 converter is used to connect an external antenna, the role of which can be played by a telescopic pin or a piece of mounting wire. The output signal through capacitor C4 is supplied to the input of the AM circuit of the receiver, switched on to the CB range (520-1605 kHz).

The converter subtracts a signal with a frequency of 8.86 MHz from the signal received at the input. Input circuit L1 C2 is set to the middle of the HF range "31 M" (9.4-9.9 MHz).

Thus, the receiver, at the input of which this converter is installed, when tuning across the entire CB range, covers the range 9.38-10.48 MHz, in the band of which lies the most densely populated HF sub-band “31 M”.

The converter can be used as a stand-alone device or mounted into the body of a radio receiver, connecting it between the antenna input and the CB-band input circuit. In this case, the AM-FM switch must provide switching telescopic antenna and turn off the power to the converter when switching to "FM".

If the converter is installed in a car receiver, it makes sense to switch its power supply circuit and antenna socket using a small-sized relay of the RES-47 type. Then it will be possible to completely eliminate the influence of the converter on the VHF-FM path.

Coil L1 does not have a frame, it has an internal diameter of 18 mm, and is wound with 0.61 PEV wire. The number of turns is 13. The tap is made from the third turn, counting from the bottom (according to the diagram). L2 - choke, wound on a ferrite ring with a diameter of 8-10 mm from ferrite 600NN-400NN, contains 300 turns of PEV 0.12 wire.

The setting consists of tuning the input circuit, using a generator, to a frequency of 9.65 MHz. If there is no generator, the setup can be done by ear, changing the circuit parameters until the reception of HF radio stations “31M” begins.

The advantage of the short-wave radio broadcasting range is its practically unlimited reception range, caused by multiple tropospheric reflections of radio waves in this range. The wave ricochets around the entire Earth. The disadvantage of the range is that the radio stations, in percentage terms, occupy very narrow frequency bands, which requires tuning accuracy and good selectivity of the receiver, and that it is AM. But still there is less interference than in the medium or long wave range.

However, the vast majority of music centers do not have an HF band (usually one or two VHF and MW, LW). At the same time, broadcasting on NE and LW is now being phased out due to the impossibility of receiving good quality reception (AM and interference) and many radio stations have either completely moved to VHF or are duplicated on VHF. In many cities of Russia now, except for the Mayak radio station, nothing is received during the day in the NE and LW. At night, the situation improves a little in that long-distance radio stations can be heard on SV, but still on HF, long-range reception is much better.

In order for the tuner of a music center with the MF (MW) band to receive signals from HF broadcast stations at its input (at the antenna jack), you need to turn on an additional frequency converter (converter), which will transfer the frequencies of the HF band to the MF band.

Schematic diagram

A schematic diagram of one of the possible options for such a converter is shown in the figure. This is a frequency converter with a combined local oscillator, made on the basis of a cascade amplifier stage. The signal from the antenna goes to the input circuit L1-C4.1-C4.3.

Through the coupling coil, the selected signal is supplied to the base of the transistor UT1, which performs the functions of both a mixer and a local oscillator. For the input signal it is connected according to a common emitter circuit, and as a local oscillator - according to a common collector circuit.

The local oscillator frequency is set by circuit L3-C4.2-C4.4-C5. Capacitor C5 ensures pairing of the settings of the input and heterodyne circuits, taking into account the intermediate frequency lying in the range of 600-1400 kHz.

Rice. 1. Schematic diagram of a simple HF converter using KT315 transistors.

Of course, such a simple method does not provide precise pairing of settings and the sensitivity is uneven within the overlapped range (5.8-16 MHz).

The complex signal of intermediate frequencies is isolated on the collector VT1, connected according to a circuit with a common base. The use of a cascade converter circuit improves performance at high frequencies, which is exactly what is needed here.

The IF signal arrives through C7 to the antenna input of the music center and is separated by its input circuits.

As already mentioned, HF broadcast stations occupy relatively narrow, percentage-wise, bands on the HF band and, therefore, tuning must be very precise. Or, it is necessary to use a scheme with extended HF bands.

In this case, our receiving system of a converter and tuner of a music center has two tuning elements - a variable capacitor C4 and a tuner tuning element. Therefore, the C4 scale can be quite rough - only the positions at which the frequencies of certain HF sub-bands are accepted can be plotted on it. And smooth and precise tuning within the sub-range is carried out using the tuner tuning organ of the music center.

Details and design

The converter is mounted on a small printed circuit board made of single-sided foil fiberglass. The contour coils are wound on plastic frames with ferrite tuning cores and aluminum screens (frames from the contours of the color modules of 3-USCT TVs). All coils are wound turn to turn with PEV 0.12 wire.

Coil L1 contains 20 turns, L3 - 18 turns. Coil L2 is wound on surface L1, it contains 5 turns, coil L4 - 5 turns with a tap from the 2nd. Coil L5 is wound on a ferrite rod with a diameter of 2.5 mm and a length of 14 mm; it contains 100 turns.

Rice. 2. Converter printed circuit board (view from the tracks).

Rice. 3. Converter printed circuit board (view from the parts side).

A block of variable capacitors with a solid dielectric from an imported pocket radio with analog tuning was taken as capacitors C4.1-C4.4. The capacitor contains four variable capacitances - two of 7-260 pf and two of 3-20 pf, as well as a set of four trimming capacitors. All these capacitors have a common wire connected, in this circuit, to the housing.

The converter is powered from a galvanic source with a voltage of 9V or from a network source providing a stable voltage of 7-12V.

On medium waves, both day and night, the airwaves are polluted with atmospheric interference and reception of distant stations is difficult. It is clear that for round-the-clock radio listening, a KB broadcasting band is required.

The sound quality in it is usually quite high (despite fading), and the reception range, thanks to the specifics of the propagation of short waves, is practically unlimited, so the time spent driving at night will not only pass faster, but will not be wasted - you can practice foreign languages.

You can supplement almost any CB radio receiver with the KB 25M range (11.7-12.1 MHz) using a simple KB converter, the diagram of which is shown in the figure. The converter is made according to a circuit with a combined local oscillator and quartz stabilization of the local oscillator frequency. The tuning is carried out by the tuning bodies of the CB radio receiver (the local oscillator frequency of the converter is not tuned).

If the mid-wave band in the radio is not needed (you intend to replace it with the KB band), the converter is connected to the break in the wire running from the antenna to the AM path of the radio (but not immediately after the antenna socket, otherwise it will interfere with operation on VHF). Power should be supplied to the converter only when the AM band is turned on.

If you supplement the radio receiver with a KB band and at the same time retain the CB band, you need to install an additional switch that will turn on the converter in the antenna circuit and supply power to it.

The signal from the antenna through capacitor C1 is supplied to circuit L1C4 tuned to the middle of the 25M range (11.9 MHz). From the output of the circuit, the signal goes to the cascade on transistor VT1, which is a quartz oscillator with a frequency of 10.7 MHz (quartz resonator frequency).

Since the output of this generator is a circuit tuned to the CB range (receiver input circuit), and the VT1 base additionally receives a KB band signal, the cascade goes into frequency conversion mode. As a result, the KB signal in the 25 M range is converted into a signal in the range 1000 kHz-1400 kHz. The local oscillator frequency (10.7 MHz) is lower than the frequency of the received signal.

If the 31M range (9.4-9.84 MHz) is required, you only need to rebuild the input circuit to it, in which case the local oscillator frequency will be higher than the frequency of the received signal and the signals of this range will be converted into signals of the 860-1300 kHz section.

The converter is mounted on a compact printed circuit board, the coils are wound on ferrite rods with a diameter of 2.8 mm and a length of 12 mm from 400 NN ferrite (preferably 100 NN). L1 contains 20 turns of PEV-0.2 wire, the coil is adjustable, so the winding, although made directly onto the rod, is not very tight, so that it can move in the coil with friction. L2 contains 300 turns of PEV 0.06, wound loosely and tightly (there should be no movement here).

On the board, L2 is immediately fixed with epoxy glue, and L1 is first adjusted by pushing or pulling the core to the middle of the selected range (the adjustment is made by changing the inductance L1 and capacitance C4; when setting to 31M, you will need to turn on an additional C4 in parallel permanent capacitor at 20-40 pf), and then it is fixed in this position on the printed circuit board using epoxy glue.

Such a converter can also be used to receive other KB bands, you just need to select a quartz resonator for a different frequency.