network transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Miscellaneous electronic devices
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circuit diagram 1, circuit diagram 2
When used as a listening device (eg rooms). One of the options is connected in parallel with the lighting lamp under the ceiling.
For transmission, frequency modulation and a carrier frequency of 94 kHz are used. The device is powered by the mains. The excess is quenched by a capacitor and the low voltage is rectified by a diode bridge. Further, it is filtered and limited by the KS520 zener diode and is used to power the output stage on VT1. The voltage taken from the KS210 zener diode is used to power the rest of the device. The low-frequency signal from the microphone is amplified by the cascade on VT2 and fed to a voltage-controlled square-wave generator on DD1 (FM modulator). The initial frequency of the generator is set, in the absence of a signal from the microphone, equal to 94 kHz using a tuning resistor.
Next, the signal from the generator is fed to the output stage on VT1. A transformer is included in the collector circuit, the primary winding of which is tuned to the carrier frequency. The transformer core and windings are insulated with PTFE or something similar. The transformer on W-iron worked very well .. in!
The setting is carried out using a power supply in the region of 27 volts, connected with a plus to point A in the diagram. Having shorted the VT2 base, the oscillator frequency is set to 94 kHz with a tuning resistor. The output stage is tuned by selecting a capacitor in the collector circuit to minimize the distortion of the sinusoid or, if there is no oscilloscope, to the maximum signal on the secondary winding of the transformer (DO NOT GET THE SECOND HARMONIC!).
RECEIVER
It was too lazy to invent anything and therefore a converted car VHF radio was used. The first local oscillator with quartz stabilization at 10,794 (10,606) kHz. Quartz at 10800 led 6 kHz lower. The standard piezo filter with a bandwidth of 300 kHz (a small one with three legs! :-) ) was replaced by a filter from the radio station "Len" with a band of 15 kHz to suppress the mirror reception channel. In place of the phase-shifting circuit, K174UR3 used quartz at a frequency of 10700 kHz (deviation less). UHF was not used, and the signal to the mixer was fed through a two-circuit band-pass filter at a frequency of 94 kHz, made on rings with data similar to the transmitter transformer.
Ready-made coils were tested for this frequency from army r / receivers r-155 (or r-873). It is she who is used in the synthesizers of these receivers in one of the PLL rings. The results were better (most likely due to the higher quality factor).
This scheme was originally conceived for communication over a radio network. That is why the carrier is 94 kHz and is located between the frequencies of the second (78 kHz) and third (120 kHz) programs. True, the power supply was made separately, and the output stage of the transmitter was loaded onto the additional winding of a standard transformer from a subscriber radio receiver. The number of turns, well, I don’t remember how many!. The receiver was connected to the existing secondary winding. Then the desire to invent and improve was gone.
BE CAREFUL WITH THE TRANSMITTER! POWER IS TRANSFORMERLESS!
Within the building everything worked with a bang! Haven't tried it further.
I do not claim authorship, because the scheme uses standard solutions that are given in many reference books.
Author: Alexey Koshcheev, UA4NFX; Publication: N. Bolshakov, rf.atnn.ru
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