[time-nuts] ok, newbie questions

[GandalfG8 at aol.com]

In a message dated 26/11/2010 23:31:32 GMT Standard Time, w2hx at w2hx.com  
writes:

Ahh.  Very interesting explanation. So is it somewhat correct to assume 
(yes,
I  know) that for a stationary (non-mobile) environment, these extra  sats
don’t make much difference? This seems to be what the explanation is  
saying.

Ok. So let me see. For a frequency standard for use in lab  equipment, it
appears that short term, phase noise and other sources of  noise are the
things to be concerned with  to get better results.  These seem to really be
accomplished with a good oxco.  However, if I  want a very accurate
time-of-day clock for long periods of time, then I  need long term stability
which is where the GPS comes in.  Do I have  this right?

So if I want a really souped-up freq standard for my lab,  then I should
concentrate on finding the best oxco I can (which may be  disciplined by the
GPS or manually occasionally calibrated to GPS), and use  the best power
supply I can find.  These seem to be what I should  concentrate on rather
than more channels. 

I do believe that I read  some stuff on the internet that the HP GPS DO's do
seem to have very good  power supplies (or converters) which contribute to
low spurs. So it seems  the HP's do have a real advantage (not just  the
name).



---------------
In searching for the best there is we may sometimes lost sight of  what we 
were looking for to start with .....
old Scottish proverb I just made up:-)
 
What gives "better" results so often depends on what you wish to  achieve.
 
You might not get the absolute minimum phase noise from something like a  
Thunderbolt, but then you might also have to ask if you need it.
 
When it's working well, and some have been known not to in quite subtle  
ways, the HP Z3801A, the only HP unit I can speak for, is an excellent  GPSDO.
What you might not notice though without reading the very small print is  
that it can take two to three weeks to settle after being repowered for  
whatever reason.
 
On the other hand, the Thunderbolt, in my experience anyway, is generally  
well settled in 15 to 30 minutes.
 
Because the Thunderbolt is so widely available it seems as though  it's can 
also be easily dismissed at times but don't underestimate it, it's an  
excellent GPSDO.
 
I would recommend that you look for one of the Chineses sellers on  Ebay 
offering T'bolts from no earlier than 2005 and with revision E  software, 
fluke.l is one good exapmple, and go for that.
There may well be an issue with the temperature sensor, much more in the  
archives on that, but replacements, if you really need one, cost pennies.
 
Once you have that, and it's stabilised, you can either use it as it stands 
 or use it to adjust your 10811 or whatever.
 
For some time now I've tended to treat my Z3801As as interesting high  
quality museum pieces, whilst using three T'bolts as references/confidence  
generators.
I then use those to calibrate the rubidium modules  and 10811s that serve 
as my lab standards, which works well for  me.
 
regards
 
Nigel
 
GM8PZR