[Test-Equipment] Frequency Measuring Test

[Dave Emery]

On Tue, Sep 24, 2002 at 12:13:43AM -0400, Glenn Little wrote:
> I wonder if they have the ability to measure their reference frequency as 
> well as some in the field. There are a number of people with GPS disiplined 
> Rubidium standards. Unless you have a Hydrogen MASER, they are hard to beat.

	So the real issue for those with modern technology frequency
standards is actually not the raw time base accuracy but figuring out
how to make a reliable measurement of the unknown signal with anything
like the accuracy of their house standard.

	Certainly a HF signal received by skywave is only easily measured
to maybe one part in 10^7 or 10^8 due to propagation effects which is
a long long way away from a couple of parts in 10^11 that a GPS disciplined
rubidium standard will do routinely.   I suppose figuring out an algorithm
to filter out the propagation induced errors might be interesting, but
certainly something very different from the frequency measuring tests
of past years, which stressed skills at calibrating and setting up 
hardware and using it skillfully.

	I could - and I suppose many many others with fully synthesized
HF rigs referenced to a 10 mhz input from a rubidium GPS disciplined 
standard could too -  measure a HF signal by just tuning it in with a
known BFO offset and processing the resulting audio with a soundcard to
make a best estimate of the frequency of the beat note minus propagation
related shifts.  And if I really was anal, I could hack the soundcard to
derive its sample clock from a synthesizer driven off the 10 mhz
rubidium standard too (eg replace the crystal osc used for timing with a
clock input from a synthesizer or even just a DDS NCO chip driven from
the rubidium).

	I suppose a local VHF or UHF signal might be measurable with
much greater accuracy, but then one gets into multipath and all sorts of
other  effects and of course the test signal only reaches a few people.



> 
> 73
> Glenn
> WB4UIV
> 
> At 11:35 PM 9/23/02 -0400, Gary Chatters wrote:
> >The latest issue of QST announced that ARRL is bringing
> >back the frequency measuring test.  Anyone here thinking of
> >participating?
> >
> >Gary

-- 
	Dave Emery N1PRE,  die@die.com  DIE Consulting, Weston, Mass. 
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2  5D 27 BD B0 24 88 C3 18