[time-nuts] Thunderbolt SV and AMU Signal levels
GandalfG8 at aol.com
GandalfG8 at aol.com
Tue Jul 22 19:41:39 EDT 2008
In a message dated 23/07/2008 00:15:51 GMT Daylight Time,
dave.g0dja at tiscali.co.uk writes:
The 10MHz output seems, as far as my old Multifunction Counter is
concerned, to be to 10.00000MHz within +/-0.00001 MHz.
The display showing 10.00003 to 10.00004 MHz all evening.
So, my guess is that my poor old counter is +/- 10Hz out, but that may
be due to the age and non-calibration of my frequency counter over the
years.
Or... The Thunderbolt 10MHz output is moving up and down by 0.00001 MHz
within a 10MHz band.
This is where I start to get to grips with the spectrum analyser that a
friend of mine lent to me. I hope...
-------------
Hi Dave
One of the problems with becoming a time-nut is that the first step,
whatever that might be, is fatal.
And after that it just gets worse:-)
Unless your Thunderbolt is very unwell, which I doubt, it won't be moving
anywhere near that much.
Not only is the reference in your counter likley to be off frequency but
it's also likely that the stability of the reference is much worse than what
you're trying to measure, and this is where the downward spiral really begins.
Earlier this year I bought an HP 53132A counter to give me the resolution
I'd decided I needed and promptly used it to measure the 10MHz output of a
Thunderbolt.
The result was similar to what you're seeing and a great disappointment,
especially as I didn't know at first whether to trust the counter or the
Thunderbolt.
However, using another Thunderbolt to drive the external reference input on
the counter gave a very different result, and immediately any variation became
just a few figures in the 10th decimal place.
It turned out that the basic reference as fitted to the 3132A was fine to
demonstrate that the counter was working, but that was it.
If your counter will accept an external reference I'd suggest using the
Thunderbolt for that and just trusting the results.
However, if the figures you've shown represent the resolution limit of your
counter then you may want to consider a counter with better resolution, still
using the Thunderbolt as a reference of course, but just watch your balance
as the downward slide continues:-)
regards
Nigel
GM8PZR
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