First you need a standard, a crystal oscillator. If you want serious
precision, you'd have one in an oven. Zero beat that with WWV. Then make a
very stable VFO and calibrate the harmonics against the crystal. Assume linear
calibration on the VFO between check points.
The military LM and BC-221 were very good units. I had one. The check points
in the calibration book were too far apart but there were others that weren't
documented that would make for more precise calibration.
I also built a frequency meter that was amazingly accurate, from a GE Ham News
project printed back in the early 1950s. It used a VFO that went between 100
kHz and 101 kHz for its full range, adjusted by a micrometer dial (military
surplus). Its harmonics would be zero beat with the unknown. Using a
successive number of harmonics would identify the harmonic number and the scale
could be interpolated to within much less than 1 kHz over the HF range.
Of course, zero beat was hard to identify so you could use an oscilloscope
lissajous pattern (if you had an oscilloscope, which I didn't). What I did was
turn up the volume and listen to the beat. When it got down near zero the
sound of the AGC surging would tell me the frequency of the beat and I could
adjust to make it stop surging.
When I got my hands on a Beckman counter I was in heaven.
Bob
On Sunday, February 12, 2017 4:01 AM, Neville Michie <[email protected]>
wrote:
Back in the early sixties I worked in a lab adjusting filters for line
transmission.
We had numerous oscillators, built to be boat anchors, and CROs set up for X-Y
display.
The lab had 100hz, 1kHz, 10kHz standards wired in.
We were expert at recognising lisajou figures. We might have several
oscillators running together,
and we could establish almost any frequency with precision.
Calibting an oscillator would not have been difficult.
Cheers, Neville Michie
> On 12 Feb 2017, at 5:08 PM, Scott Stobbe <[email protected]> wrote:
>
> I was inspired recently coming across a Lampkin 105 frequency meter, as to
> how frequency measurement was done before counters.
>
> Certainly zero-beating a dial calibrated oscillator, would be one approach.
>
> Is there a standout methodology or instrument predating counters?
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