[time-nuts] Vintage Frequency Measurement
bob91343 at yahoo.com
Sun Feb 12 12:00:48 EST 2017
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.
On Sunday, February 12, 2017 4:01 AM, Neville Michie <namichie at gmail.com> 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 <scott.j.stobbe at gmail.com> 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?
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
More information about the time-nuts