[time-nuts] Another "atomic" clock question

GandalfG8 at aol.com GandalfG8 at aol.com
Sun Mar 2 12:27:02 EST 2014

In a message dated 02/03/2014 16:06:49 GMT Standard Time,  
bob91343 at yahoo.com writes:

Yes  Nigel, it's a waste of time but so are computer games and going to 
Disneyland  and such.  We do it because we get pleasure, and nobody can 
criticize  that.
Hi Bob,
I'm not sure where the waste of time comes in, that's certainly not  
something I was suggesting, although perhaps not quite so convinced when it  comes 
to computer games and/or Disneyland:-)
It might become time consuming, even to the point of becoming an obsession, 
 but that still doesn't stop it being a very rewarding obsession:-)
I'm sorry, I had assumed you would at least be somewhat familiar with what  
I was referring to.
Trimble made a GPS disciplined oscillator called the "Thunderbolt",  that 
was a reference to a comment in a previous reply, available on the  surplus 
market but now more expensive than they used to be.
The other unit I mentioned was what I considered to be a reasonably  priced 
Trimble are just one manufacturer of such items, it's also possible to  
build your own, so some searches on GSP disciplined or conditioned  
oscillators, GPSDOs for short, might indeed be very worthwhile.
Basically, what they do is correct the drift of a  local oscillator, 
usually contained within that unit  and often 10MHz but not necessarily so, 
against the frequency  references used by the GPS satellites, and this gives you 
your standard signal,  so as well as the unit itself you need a GPS antenna 
to receive the satellite  signals.
There's a variety of factors that will affect resolution and stability  but 
1 part ber billion should be straightforward plug 'n go, and I would expect 
 a few parts in 10^10 with very little effort.
Because of the way this works the GPS reference itself doesn't  need any 
additional calibration, so if you did eventually decide to go  for a rubidium 
oscillator, as you suggested you might, this could be one  way of 
calibrating that.

I am a bit confused over your mention of Trimble  units.  I'm not familiar 
with them or what they are supposed to do.   I better do some homework.

I know if I use an X-Y 'scope with two  reasonably clean signals I can 
adjust one for a stable pattern and so,  depending on how long it holds still, 
know how close the two frequencies  are.  I can get one signal from my 
counter time base, but where do I get  the standard  signal?


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