DTMF Decoder (CB25048E)

This circuit was found in the 1987 Radio Electronics magazine. The components used are integrated circuits of the time.

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x10 frequency multiplier (CB21078E)
Found in American documentation from the 1990s, this TTL circuit operates at frequencies typically up...
Simple 2 to 12 MHz Receiver (CB1451E)
The coil L2 has 64 turns of wire 28 or thinner wire in a 1 cm form coreless and L1 10 turns on L2....
4 to 100 MHz XTAL Oscillator (CB12710E)
This circuit, shown in the figure, can operate from 4 to 100 MHz, based on a 2N2222 transistor or...