28 August 2014
BUILD IT YOURSELF
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.
FREQUENCY COUNTERS AND
By Robert Reed