A simple stereo generator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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Having built such a device, radio amateurs will greatly facilitate the tuning of stereo radio receivers and stereo decoders. With its help, a complex stereo signal and high-frequency oscillations with frequency modulation can be obtained from a conventional low-frequency stereo signal.

The schematic diagram of the device is shown in fig. 1. It is a stereo generator, which includes a quartz subcarrier frequency oscillator on a VT3 transistor and DD1, DD2 microcircuits, a polar modulator on VTI, VT2 transistors and a high-frequency (HF) generator on a VT4 transistor with a frequency modulator (FM), the functions of which are performed by varicap matrix VD1.

Fig. 1

The device works as follows. The low-frequency stereo signals of channels 1 and 2 alternately with a subcarrier frequency of 31,25 kHz modulate the signal of the RF generator. the functions of switches are performed by transistors VTI, VT2. The necessary pre-emphasis is introduced by RC circuits C1R3 and C2R4 with a time constant of 50 µs. The complex stereo signal (CSS) generated by the polar modulator is transmitted through the filter plugs L1C3 (suppression of the third harmonic of the subcarrier), L2C4R9 (partial subcarrier suppression) and the R10C5R14 circuit to the frequency modulator.

The RF generator frequency was chosen to be 69 MHz, which corresponds to the middle of the broadcasting range. The power emitted by such a generator is about 200 μW, which is sufficient to receive high-frequency oscillations with frequency modulation at a distance of up to several meters to an antenna in the form of a 1 m long piece of wire or a telescopic antenna of the receiver. With the ratings of the parts indicated on the diagram and the input low-frequency signal of 250 mV, the frequency deviation of the RF generator is about 50 kHz.

To power the stereo generator, you can use a current source with a voltage of 4,5 ... 6 V, for example, a 3336 battery, the current consumption in this case is 1.5 ... 2 mA. Coil L1 (inductance 2,5 mH) is made on a K12X8X3 ring magnetic circuit made of M2000NM-3 ferrite and has 200 turns wound with PEV-2 0,27 wire, and L2 (18 mH) on a K40X25X7.5 magnetic circuit made of M2000NM-1 ferrite , number of turns 360, PEV-2 wire 0,6. Coil L3 (1 ... 2 mH) is wound on a unified four-section frame made of polystyrene with a PS2.8X 10 magnetic circuit made of M600NN-3 ferrite, contains 200 turns, wire PEV-2 0,12. The generator coil L4 is frameless, the inner diameter of its winding is 5 mm, the number of turns is 5, the wire is PEV-2 1,0.

For installation, fixed resistors MLT 0,125 and trimmer - SPZ-226, capacitors - KM-6, KT-1 and KSO, quartz - from the set <Quartz-2". XS1 socket - ONTS-VG-4-5 / / 16- P, switch SA1 - MT-2.

Set up a stereo generator using an AC voltmeter, which is connected to point B (Fig. 1). When setting the L1C3 and L2C4 circuits to resonance, the device should show a minimum voltage. Then, alternately connecting the device to points A and B, by selecting the resistor R9, the voltage difference at these points is achieved by 5 times.

Along with such advantages as simplicity and slight distortion of the CSS, the described device has a significant drawback - the inability to adjust the stereo decoder blocks directly. This drawback can be eliminated by using a source follower (Fig. 2) on a transistor VT1', connected before the FM, with a separate KSS level control and output sockets XS1'. Filter R2', C1', R3', C2', R4'. C3' serves to suppress the higher harmonics of the subcarrier signal.

pic.2

When the source follower is operating on the FM, a smoother and in a wider range regulation of the frequency deviation of the RF generator is achieved. The described device was used by the author to tune the stereo path of the Victoria-003-stereo tuner. At a frequency of about 800 Hz, a crosstalk of 32 dB was obtained.

See [1] and [2] for how to set up stereo decoders. As a low-frequency stereo signal, you can use the line outputs of stereo tape recorders and electric players. Only important. so that the signal level does not exceed 250 mV, and the output resistance of the signal source is within 1 ... 2 kOhm.

Literature

1. Topilii I. Stereo decoder prefix. - Radio, 1977, No. 6, p. 31-32.
2. Filatov K. Stereo decoder with adaptively adjustable bandwidth. Radio, 1986, No. 11, p. 29-32.

Author: S. Ogoreltsev, Sukhumi; Publication: N. Bolshakov, rf.atnn.ru

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