[time-nuts] Coarse adjustment of PRS-10 with 5335A

Bob Camp lists at rtty.us
Mon Sep 2 16:27:57 UTC 2013


Hi

1) Because it's way more fun to do it this way
2) Because some / most PRS-10's don't have the 1 pps input enabled in the firmware they have loaded into them
3) Because you have more control over when you do / don't bump the frequency (you can see what's going on). 

Bob

On Sep 2, 2013, at 12:21 PM, Robert Darby <bobdarby at triad.rr.com> wrote:

> This is a dumb question but why not let the PRS-10 set itself using the 1PPS input and an appropriate time constant?
> 
> Thanks,
> Bob Darby
> 
> On 9/2/2013 12:09 PM, Bob Camp wrote:
>> Hi
>> 
>> Ok, you are fine with the 10 MHz reading on the 5335 to get things "sort of close". Once you get past about 1.0x10^-10 you may want to switch over to a pps based approach. More or less:
>> 
>> Fire up 5335 with pps from gps / gpsdo and from the PRS-10. (I'm assuming it's a GPSDO)
>> Watch the reading for a few seconds, record the average and the time.
>> Go have lunch / nap / beer / what ever.
>> Check the time and the reading.
>> Do the math
>> Bump the PRS-10
>> Step / repeat at the couple hour time interval for a day or so.
>> Drop back to a couple days, check and (maybe) adjust.
>> Drop back to once a week, check and (maybe) adjust.
>> 
>> Note that the 5335 only has to be on while you are actually observing the pps. No need for the heat / wear and tear the rest of the time. Your pps needs to run all the time, but that's only a problem if there is a power outage.
>> 
>> The advantage of doing it this way is you get both high resolution and averaging at the same time. Since there's pretty much nothing to set up (no computers / no GPIB) it's reasonably foolproof. Assuming that the 5335 is doing it's thing and that the GPSDO is good to roughly the same level:
>> 
>> 3 hours is 10800 seconds
>> your reading is good to 3 ns (2 on the GPSDO and 1 on the counter)
>> you  get +/- 3.0x10^-9 at 1 second
>> you get about +/- 3x10^-13 at 3 hours.
>> 
>> Since the ADEV of the Rb is much better at the longer Tau's, the data you are using is probably a better bet than anything you can do in less time.
>> 
>> Bob
>> 
>> On Sep 2, 2013, at 9:20 AM, Paul <tic-toc at bodosom.net> wrote:
>> 
>>>> If you are trying to measure frequency with the 5335 rather than pps signals
>>> Ah, I was unclear.  I'm adjusting the 10MHz output.  It was pretty far
>>> out when I got it.
>>> 
>>> --
>>> Paul
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> 
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