[time-nuts] Vintage Frequency Measurement

[Alan Melia]

I am surprised no-one mention the 3-beat method, which was fairly common for 
Hams with comms receivers. You put the BFO on and adjusted so the main slow 
beat modulated the level of the output tone. You can judge zero beat to much 
better than 0.1Hz that way probably near as low as 0.01Hz. (1E-9 for 10MHz 
!!)

Lissajous figures are not ideal either but don't require a comms receiver, 
(but do require a 'scope with X-Y facilities :-))  ) a better technique 
certainly for fixed frequencies (stand comparison) uses Z-mod on the scope 
or a running "toothed wheel" display see Radio Laboratory Handbook by 
Scroggie.

Ah and the BC-221......

Alan
G3NYK



----- Original Message ----- 
From: "Bob Albert via time-nuts" <time-nuts at febo.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Sunday, February 12, 2017 5:00 PM
Subject: Re: [time-nuts] Vintage Frequency Measurement


> 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 
> <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?
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