[time-nuts] Checking accuracy of Rubidium standards

[Steve Rooke]

Bruce and Joe,

I have been enjoying this discussion too.

2008/11/9 Bruce Griffiths <bruce.griffiths at xtra.co.nz>:
> J. L. Trantham wrote:
...
>> That is something that I have not yet had a chance to contemplate as far as
>> how to measure.  It would appear to require a particularly stable (pure)
>> source as a reference though.  Various multiplying or dividing protocols
>> would seem to introduce a host of other variables that would seem to be
>> difficult to account for though they might accentuate an impurity in the
>> signal in question.  I have read Bruce's comments and I still do not
>> understand the basics of time stamping or how a sound card might provide
>> this.

> There is sufficient information available from the sound card samples to
> calculate the input signal at any time between 2 samples and in
> particular derive the time at which the signal crosses zero.
> This is the time stamp for that zero crossing.
> The frequency and ADEV of a signal can then be calculated from such a
> sequence of time stamps.
> However it is necessary to either calibrate the sound card sampling
> frequency or lock it to a known frequency.
> The method used to interpolate between samples is called WSK (Whittaker
> Shannon Kotelnikov) interpolation.

Given Joe's comments, doesn't making ADEV measurements rely on highly
accurately spaced sound card samples and the nature of system based
upon this hardware affect the accuracy of any such based system? Does
the accuracy of the measuring system not have to meet or exceed the
accuracy of the DUT?

73, Steve
-- 
Steve Rooke - ZL3TUV & G8KVD
Omnium finis imminet