actually if the "oscillator" is stabil enough, with a very long time
constant one could kill the phase modulation of the new WWVB format
73
Alex
On 8/23/2014 6:27 PM, Bob Camp wrote:
Hi
If you lock an Rb to GPS, you need / want / should do it with a *very* long
time constant. Numbers in the one day to several days range are commonly seen.
If you lock it up with a tighter (shorter time constant) loop, it will just
wander around as it follows the GPS input. That’s what would happen if you hook
your Rb to your Trimble and turn on the disciplining on the Rb. It will
significantly degrade the stability of the Rb.
If you have a temperature stable environment (or create one) you can get some
very good results with an (good) Rb locked to a (good) GPS via a proper long
time constant setup. It’s not easy, but it can be done.
Bob
On Aug 23, 2014, at 6:31 PM, Ed Palmer <[email protected]> wrote:
Hi Dave,
On 8/23/2014 3:51 PM, Dave M wrote:
Thanks for that suggestion, Ed. After a bit of reading in the X72 Reference
Guide, it appears that the X72 does have a 1PPS input. That would be
considerably easier than trying to interface the Rb into the GPSDO. Still
trying to understand what the manual is telling me. Next thing is to determine
if my unit has that option enabled (firmware option). That will be a chore for
after the holiday... really busy next week.
What would that (1PPS disciplining) do for me... in terms of maintaining the Rb
frequency accurately set? Would it be as accurate as having the Rb disciplined
via the EFC input?
It's kind of overkill, but by connecting the 1 PPS from the NTBW50AA to the
X72, the X72 will be disciplined to the 1 PPS so the frequency will be
accurate. The question is how well will it be disciplined, i.e. what will the
Allen Deviation graph look like. I have a few X72 and SA-22c (X72's cousin),
but none of them have that option. I don't know of any published data on it.
Maybe you can tell us how well it performs.
In general, I just don't see the point of disciplining a Rb standard to GPS. I
don't understand what will be gained by doing it. I have a Z3801A and a Tbolt
plus a free-running FRK as a house standard. I occasionally compare the FRK to
the Z3801A but the drift is so low (~1e-12 per month over 9 months) that I see
no reason to link them.
One exception that I recently discussed on another forum was a guy who lives in
a ground floor, north-facing condo. He might need to have a disciplined Rb
standard due to poor GPS visibility.
Ed
Thanks,
Dave M
Message: 5
Date: Fri, 22 Aug 2014 16:19:45 -0600
From: Ed Palmer <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] EFC info on Trimble 34310-T OXCO
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Have you checked your X72 to see if it has the 1 PPS discipline
option?
That would be a lot easier (and probably better) than your proposed
transplant.
Ed
On 8/22/2014 12:39 PM, Dave M wrote:
Does anyone have any info on the OXCO in the Nortel/Trimble
NTBW50AA-17 GPSTM receiver? The OXCO is labeled as Trimble 34310-T.
I see some Trimble 34310-T oscillators on Ebay with pinouts labeled,
but no other info.
Specifically, I'd like to know the EFC characteristics for it. I'm
thinking of the possibility of pulling the OXCO out of the GPSTM and
subbing in a 10 MHz Rubidium, and using the GPSTM to discipline the
Rubidium. My Rubidium is a Symmetricom X72, recently purchased. It
seems to be working well.
Does anyone know the differences between the three OXCOs used in the
GPSTM receivers ("T", "T2" and "Oak")?
Thanks for some insight,
Dave M
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
