We found this circuit in a 90s Popular Electronics. The circuit uses a pickup coil that consists of 100 to 200 turns of wire 28 around the cable to be monitored.
This application of the RCA integrated circuit released at the time was found in the August 1970...
These basic filters, the second one being operational, were published in the November 1973 issue of...
This circuit adds the voltage from the secondary of a transformer to an outlet connected to the...