FREQUENCY COUNTERS AND RETROFITTING

摘要

Frequency counters have always fascinated me. Even a mediocre model has higher accuracy than any other instrument on a test bench. My first such counter was a Lampkin micrometer frequency meter which was popular in the mid-1960s. This well-designed instrument was based on a narrow range variable frequency oscillator (VFO) that was tuned with capacitor plates. The VFO was attached to a modified machinist's micrometer with a calibrated dial plate. After a 15 minute warm-up, the VFO was zero beat to one specific frequency against a very stable compensated crystal oscillator. From that point, each frequency being tested was checked using a lookup table after zero beating the Fo under test to the calibrated dial reading.