Modification to Workman FC-30BT

The Workman FC-30BT is an inexpensive frequency counter that makes an excellent display for the 160/80 meter VFO, however it suffers from two problems. Instead of reading all zeroes with no input the digits wanders aimlessly displaying random frequencies. Also, when presented with a TTL-level, square-wave input the counter has a tendency to lock onto and display harmonics of the operating frequency. Both problems are related to the high-gain amplifier used as the input stage. The modification presented here removes the preamplifier stage and feeds the input directly to the counter module and restores stable operation with a TTL-level input signal.

Remove the following components: C2, C8, Q7, R18, R26 and R33.

In place of C2 install a jumper.

Install 10K and 100K ohm resistors in the locations shown.

This completes the modification. Stable operation should result with a TTL-level input signal from the VFO.