[time-nuts] Beginners GPS locked frequency counter question

[Nick Sayer]

> On Oct 31, 2015, at 3:29 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 
> Some people is very fond of using the frequency measure of counters, I've grown more and more sceptic to it for a number of reasons when doing ADEV and friends, then I use TI that avoids a number of issues.
> But that is a much more involved story.
> 

In doing my evaluations of my GPSDO, I’ve tried two configurations:

1. Feeding a reference into one input and the test signal into the other and asking my 53220A to give me the time difference between the two, and then having TimeLab fetch that.

2. Feeding a reference into the external reference input and the test signal into input 1 and asking for the frequency, and having TimeLab fetch that.

So far, #2 has given me (very) slightly lower AVARs. My guess as to why is that if you’re reading phase differences, then that is very sensitive to the accuracy with which you time the sampling. I’m interrogating the TIA with a virtual machine over WiFi, so I don’t have any reason to expect that that timing is going to be exceptionally accurate.

If anyone has any additional insight or corrections to my understanding, I’m all ears.