[time-nuts] Measuring Phase difference between different GPSDO

Fri May 3 16:48:19 UTC 2013

Am on the way to doing my first 'phase difference' with timelab - takes an hour :)

This is good stuff, everything went so smoothly, from installing the OS to using Timelab.

Now I have to figure out how to measure and set the xtal turning temperature for this bunch of Z3805A's I have here.

I have a Z3816A that is super stable. SYST:STAT? usually reports 0.0us for PU, sometimes it will go out as far as 0.2us, but very rarely :p

So I am planning on using that guy as my reference to tune the Z3805A's.

How does that sound?

Many thanks,
mark

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
Sent: Saturday, 4 May 2013 1:09 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Measuring Phase difference between different GPSDO

Hi

Grab an old garage sale category PC, blow the dust out of it and fire up the GPIB. Once it's all working next steps:

Check out TimeLab and EZGpib. Both are pretty good at talking to "stuff".
TimeLab does support the 5370, not sure about the other programs.

If you have two GPSDO's with pps outputs, feed one into each channel on the 5370. Put it in start / stop mode and you should see the difference between the two. Since they can be either ahead or behind each other things can get a little messy. 

Next, go to the software that runs your GPSDO and look for the "cable delay"
setting. Adjust it on one GPSDO so it's always early (or late) by a couple hundred nanoseconds. Now fiddle the cables to the counter so it reads a couple hundred nanoseconds and not almost a full second :).

At this point you are reading frequency to a very high resolution. The GPSDO's likely are only good to a couple of nanoseconds at 1 second. The counter should be good to ~0.02 ns.

Run like this for a few minutes and see what you get.

-----------

Now that you have conquered that approach it's time to tear it all apart and try something new.

Feed the 1 pps into one input of the counter (just like before). Hit the other input with 10 MHz. You now will get a reading in the 0 to 100 ns range. Each time a cycle slips past the 1 pps the reading will skip from 99.xxx to 0.xxx ns. That's called a phase wrap around. Click the appropriate boxes on which ever software you are running and it should take care of the wrap.

--------

Either way the software should show you frequency, and frequency stability. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Mark C. Stephens
Sent: Friday, May 03, 2013 10:07 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Measuring Phase diference between different GPSDO

Hey Bob, I was thinking the exact same thought, and I found a NI PCI-GPIB card in a PC with a dead HDD.
These appear to be 5V PCI cards so I can't stick it in a nice rack mount server with raid as they all seem to be 3.3v PCI.
So I put a new HDD in the PC and I have stuck WinXP on it.
Now I am awaiting further orders!  ;)

mark

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
Sent: Friday, 3 May 2013 9:21 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Measuring Phase diference between different GPSDO

Hi

If you have a pile of GPIB cables, you may also have a GPIB card on a PC.
You will have a lot more luck finding free software to read and log the data from the 5370 than from the 3575. As mentioned before, the 5370 will be much more accurate / higher resolution in this application. 

Bob

On May 3, 2013, at 12:28 AM, Mark C. Stephens <marks at non-stop.com.au> wrote:

> According to http://www.realhamradio.com/z3801a-turning-point.htm they 
> use
a HP 3575A phase meter to perform the measurement.
> Or perhaps I have misinterpreted the whole thing?
> 
> 
> I do have a temperature controlled workshop that is always 24 degrees 
> so
hopefully thermal drift won't be too much of an issue.
> 
> 
> mark
> 
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]
> On Behalf Of lists at lazygranch.com
> Sent: Friday, 3 May 2013 12:12 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Measuring Phase diference between different 
> GPSDO
> 
> Meditating on this a bit, I assume in a strict sense, you can only
consider GPSDOs phase locked if they are disciplined from the same GPS.
> 
> Or is this being pedantic?
> 
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