This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
This circuit detects signals in a wide range of frequencies, indicating their strength in an...
This traditional two-tone alarm configuration with the 4011 integrated circuit was found in a 1998...
This circuit was found in the June 1980 issue of Radio Electronics magazine. The circuit uses an...