And here would be my planned approach to the second option. A micro-controller (PIC, PICAXE, ATMEL, etc.) programmed as frequency counter of particular kind. Lets count as precisely as possible around 2kHz.
Here are some ideas how to display the deviation from 2kHz:
- 5 LEDs: red (+/-10 to -+/-5Hz), amber (+/-4 to +/-2Hz), green (from -1Hz to +1Hz)
- 7 segment display: deviation in Hz, decimal dot a negative sign indicator
The following idea is for the more advanced builder. It should also be seen as a modification to the receiver. The clarifier-potentiometer could be replaced by some circuitry creating/controlling the clarifier varactor. PWM could be an idea here. The concept would be to "visit" a known carrier, activate the counting and adjust the varactor voltage such that the counter counts a 2kHz beat. Now deactivate counting and keep the varactor voltage constant. Actually, in a grabber setup, one may consider to have such "calibration visits" periodically (maybe every 3h) executed by the micro-controller, e.g. by switching between memory channels.