[time-nuts] Basic GPSDO finessing re frequency accuracy

[Bob Camp]

Hi

If it’s a GPSDO with a long time constant, the ADEV in the 1-10 second range should be pretty much “all OCXO” and very 
little influenced by the GPS. 

Already that makes a bunch of assumptions that may or may not be true:

1) The GPSDO *has* an OCXO and it’s properly designed
2) The unit has been on for a week or so and it locks up fine
3) The position and elevation mask are not so bad that it goes out of GPS lock
4) The environment is stable and you are not on something like a missile.

There are probably another dozen things that could be added to that list…

Some things to note:

 1)  As long as you don’t *change* the antenna delay (cable delay) it will have no impact on the frequency 
accuracy at all.

2) Assuming (more assumptions) that it is an L1 GPSDO, ionosphere will contribute more to the daily drift
that minor errors in position. 

3) Having many satellites in view at all times is pretty much a requisite for good performance. Antenna 
location matters. 

Again, there are a few dozen more things that could go on that list as well.

Bob 

> On Jul 1, 2015, at 11:18 AM, Alan Ambrose <alan.ambrose at anagram.net> wrote:
> 
> Hi,
> 
> Does anyone have any data / a feel for how ... antenna delay accuracy  and/or  elevation mask  and/or  hold position accuracy ... translate to frequency accuracy for short term measurement i.e. in the 1-10s tau range? That is, which should I focus on, which not?
> 
> Kind Regards, Alan
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