[time-nuts] Vintage Frequency Measurement

Alexander Pummer alexpcs at ieee.org
Sun Feb 12 13:14:44 EST 2017


There was also one generator which you could tune to beat the frequency 
in question the generator was a frequency synthesizer without any 
digital part that was the famous Schomandl FD!  see here


      SCHOMANDL-FD1-FDM1 FREQUENCY METER,
      https://elektrotanya.com/schomandl-fd1-fdm1_frequency_meter.pdf/download.html
      there they have the circuit diagram and a complete service manual
      also,  the circuit was not that complicated

a similar Dekadischer Service-Frequenzmesser 
FD100http://www.radiomuseum.org/r/schomandl_dekadischer_service_frequenzmesser_fd100.html, 
on which I worked to was made with solid-state components
73
KJ6UHN
Alex
[Dr. Alexander Pummer a former design engineer of Schomandl KG in Munich 
Bavaria/Germany]


On 2/12/2017 6:07 AM, Bob Camp wrote:
> Hi
>
> 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.
>
> Bob
>
>
>> 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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