[time-nuts] GPSDO using 100Hz

[WarrenS]

...

> Also if you would, I'd like to have a better understand of
> what seems like an over obsessions with Low Noise GPSDO.
> I do understand the need (or at least the desire) 
> to have low noise oscillators when using them directly for high 
> frequency and/or short time scale data taking applications, 
> and the need for a good stable oscillator where it must maintain 
> frequency if the GPS signal is lost, 
> BUT it sounds like this is not what a large percentage of the 
> second hand GPS trackers discussed here are used for. 
> It does not seem like it would matter what the noise of the internal 
> OSC is, if the unit is only being used for averaging things over longer 
> periods such as looking at phase drift over time when doing freq checks. 
> Any data taken at a period of say 1000 second to several days is 
> pretty much limited by the noise of the GPS and not the Oscillator, 
> so why is there the desire for the low noise oscillators in these cases?
>
> Warren
> *****************
>   
Often the use of a low noise OCXO is mandated by unstated applications
such as:

1) The OCXO output is used to drive the external frequency standard
input of a counter.

2) The OCXO output is used calibrate other oscillators to 1E-9 or
perhaps a little better and averaging over 1000 seconds or so during
adjustments isnt a sensible option.

3) The OCXO output may be used to control the frequency of a microwave
transmitter and/or the LO of a receiver which requires low drift and
phase noise.

4) Obsession

Bruce

****************
Bruce

Thanks, I'd  forgotten about really good counters with resolution better than a1 ns,
 because I don't have one, Wish I did. 

and I understand the microwave and Obsession needs,

But  as far as #2, calibrating to 1E-9 or better, am I forgetting something else?
I think even the poorest Osc's, that would ever be put in a GPSDO,  
have phase noise and drift of under 1 ns, so in 1 sec it could  do 
1E-9 or in 10 sec 1E-10.  Are you saying that 1 to 10 seconds may 
be too long of time to average over?

Warren