Found in an American 1980s documentation, this circuit compares signals from two TTL sources, providing an output that depends on the frequency difference. The circuit can be used as a shield.
The components of this circuit are from the time of its publication in the 1980s. Modern...
This circuit was found in the National component manual which is not currently simple to obtain....
September 2016 - It can be obtained from Mouser Electronics modules with 2.4 inch from 4D Systems...