[time-nuts] Vintage Frequency Measurement

Bob Camp kb8tq at n1k.org
Sun Feb 12 09:07:59 EST 2017


Counters go back at least into the early 1950’s. I started out with fully vacuum 
tube (except for diodes) counters obtained as surplus in the mid 1960’s. They
used some odd gas filled triodes. Everything in them could have been on the market
in 1947. They were not a common thing until the late 50’s. 

Prior to that (WWII era) the standard approach was to use a heterodyne frequency
meter. They could be quite complex. I once passed up a “deal” on one that spread 
out over several rack cabinets. The idea was that you produced a beat against this or that
and then beat it again against something else. Ultimately a meter or scope showed
you the phase offset. 

The heterodyne approach lived on in the era of the counter using a synthesizer as
the reference. The beat note went into an analog meter based audio frequency meter.
It allowed you do do cute things like servo to a target when grinding or plating something 
to frequency. 

One key thing to keep in mind: in the 1930’s it is rare to find a frequency spec that is 
not stated in percent (with some zeros involved). A  tight spec was in the 20  ppm 
(or 0.002% ) range. The idea of a heated crystal as a reference was a “national 
standards” sort of thing in 1935. The crystal industry as we know it today really only dates
back to 1939. Before that the number of producers and the volume produced
was *very* small.


> On Feb 12, 2017, at 1:08 AM, 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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