Hi Dave,
My question was more centered on determining your expectations. I ran
into an even worse condition with the cheap sound card, in my shop
computer, I used for the Frequency Monitoring Tests (FMT) ran by Connie
(K5CM). Being in a space with no temperature control at all, the sound
card had a 7.0 Hertz variation over a few minutes. Clearly, it was a
crystal going wild.
As an experiment, I decided to rip out the crystal and replace it with
the output of a HF synthesizer dialed to the proper frequency. My
synthesizer, and other LAB equipment, is locked to my house standard
which is monitored (not controlled by) with GPS.
As expected, the results were spectacular ! I ended up with a
measurement process that had a resolution of 120ns, and maybe somewhat
less. At 1000 Hertz that is an uncertainty of +/- 1.2e-10. I did not
try to account for ground loops or other anomalies; and the sound card
was some cheap $18 item with no spectacular ratings in and of itself.
I am now finishing up on a project to replace my expensive commercial
synthesizer so it can return to test equipment duty. If you are
interested in what I am doing in that regard, email me about it off list.
As for the TS-2000 radio, I have not studied it, per se. But like a lot
of these modern radios there are several possible error points within
their design that could cause offsets and drift that may affect the
outcome depending upon your application.
However, if you are using a common analog detection type radio in the
"AM" mode, then the radio does not matter to the outcome. The radio
only serves as a mixer, albeit an expensive one. For example, when
comparing an approximate 10 MHz unknown signal, the mixing action
provides four (4) more decades of resolution if the output of the mix is
1000 Hertz. If using a modern DSP radio in the "AM" mode you may have
to account for possible slight errors in the internal codecs (A>D/D>A).
The only two error points that matter (using "AM" in the above example)
is the local signal generator used to beat against the unknown incoming
signal and the computer's sound card stability. If both are tied to
your "House Standard," then it is totally up to the quality of your
local standard's stability and accuracy.
Bill....WB6BNQ
quartz55 wrote:
Well, Bill, I just don't know. I think that's why I asked. However, I did
measure it again over 2.5 hrs and I got a roughly 500uHz drift pretty much all
in one direction. I'm wondering if this is telling me I'm cabable of measuring
1mHz with some amount of success, I realize I will have to keep repeating this
to see what happens in the long term. I've never tried to measure these small
increments before and was wondering if others have had success doing this or am
I chasing a rabbit down a hole? I did try using the WSPR software to measure
freqs and that seemed to be all over the place, plus there's no way to record
it over time except manually.
I tried recording the WWV 500/600 Hz AM audio freqs with Speclab and it's so
noisy it's hard to get a good plot, but from looking at the plots I did make it
seems to be in the range of 20mHz variation, but pretty much centered on the
freqs.
I also measured some AM stations and I had drifts of 56 mHz for a 1030 KHz
station, and I have measured the DSP drift as around 14 mHz. Do the AM
stations really drift around that much? I thought they were pretty stable.
When I measure the service monitor locked to the Rb, I get much less drifts
than actual stations, like I said, around 15 mHz and that seems to relate to
the fan in the TS2000 going on and off.
Dave
N3DT
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