[time-nuts] Thunderbolt SV and AMU Signal levels

[GandalfG8 at aol.com]

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