send-receive ident

Some radio amateurs like to give an identification signal at the beginning and end of a message; others frown upon this practice which they find disturbing. If you belong to the first group, you may find this circuit useful as it gives an ident signal automati- cally when the transmit/receive key is pressed and just after this has been released again. The two signals are identifiable by being slightly different in frequency. XOR gate N1functions as a monostable, whose output is high for a short time after its inputs either change from high to low (at the onset of a transmission), or from low to high (at the end of a transmission). Its out- put is applied to an oscillator, N2/N3, and to the transmit/receive switching section. When the input pin 6 of N 2 is high, this XOR gate functions as an inverter, so that the oscillator generates a short tone in the medium audio range which is fed to the micro- phone via limiter D4/ D5. The fre- quency determining network is earthed via C1 and ...