This circuit was found in a 1945 publication. The circuit was stated to be part of a walk talkie. Note that, as it is a portable assembly, it was powered by batteries. The jack was for microphone insertion.
This amplifier, common in 1986, uses a hybrid integrated circuit that can offer some difficulty to obtain...
The basic idea of this 1989 circuit is to trigger a relay for a while when a call signal occurs on...
Although the system is experimental and should not be adopted by the arrival of digital radio, for those...