This circuit was found in a 1980s documentation for amateur radio. The circuit is for 9 MHz signals and values in parentheses for FI of 455 kHz. The circuit can be adapted to other frequencies.
May 2016 - Mouser Electronics is already sourcing the new modules from Murata MAGICSTRAP forUHF RFID....
May 2017 - Texas Instruments' new OPAx388 operational amplifiers can now be purchased from Mouser...
This circuit is from the time when cars used contact breakers. This 80's version measures the dwell...