Elektor Team
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Call Tone Generator

Call Tone Generator
*see text 5x iN4148 062 RADIO & TV Amateur VHF relay stations are normally actuated by a 1750 Hz call tone. This may give problems when the relevant sending equipment has no internal call tone generator, or it has one whose frequency is not sufficiently accurate, or whose tone duration is not long enough to securely energize the relevant relay. These problems can be overcome by the stand-alone generator described here. Simply placed in front of the microphone, it makes absolutely certain that the relay station is actuated. The generator consists of a quartz oscillator, a frequency counter and a buffer-amplifier, all contained in just two cmos It is powered by a 9 V PP3 battery, from which it draws a current of around 5 mA. Gates N1 and N2 form an oscillator that is controlled by a 3.27680 MHz crystal and provides clock pulses to IC2 which is connected as a programmable scaler. Diodes Dl-D5 determine the divide factor of 1872. Counter output Q1 thus provides the wanted 1750 Hz si...
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