Discussion:
GPSDO uncertainties
(too old to reply)
donald collie
2018-10-08 01:59:12 UTC
Permalink
I have a GPSDO which has a Trimble receiver, and Trimble OCXO inside.[I
think it runs Lady Heather] What I would like to know is what uncertainty
the 10MHz output will be with a 10 second count.This presumes that the
GPSDO is receiving satellite signals, and the OCXO is being suitably
diciplined. Should I expect 1 part in 10E12?, 1 part in 10E10?. This device
gives superior performance to an OCXO barefoot - but how much better? Would
somebody in the group who knows the answer, please wax elequently.
Thankyou,.................................................................................................Donald
B. COLLIE
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Bob kb8tq
2018-10-08 15:11:00 UTC
Permalink
Hi

The question becomes very much, what confidence level are you after? Is 99%
good enough? Are you after 99.9999%? Obviously the stability gets worse as
you crank on more nines.

Next layer to the onion is - how long have things been running and under what
conditions are they running? A few days is probably the minimum for any sort of
reasonable performance. A month or more will indeed help a bit. A stable temperature
environment is also going to have a direct impact on performance.

Things like survey position and antenna location ( number of sats viewed at all times)
will have a more subtle impact on frequency. Solar storms and ionospheric stability (sun
spot cycle) eventually get into the picture if you put in enough nines.

So simple answer: better than 2x10^-9 with any practical number of nines involved. Better
than 2x10^-10 with rational numbers (99.9 or 99.99). Maybe 2x10^-11 at the 99% level, but
probably not.

Since this is a very non-standard measure your numbers may not match my numbers. ADEV
was invented primarily because this sort of measure has so many issues. One of the issues
is that you need a *lot* of data to even begin to estimate the confidence levels and they are
very dependent on data set size. A typical spec tends to have weird stuff like “99.9%
based on 4 out of 5 runs of 100 hours”. Statements like that tend to make a statistics guy
groan ….(or throw something at you).

Bob
Post by donald collie
I have a GPSDO which has a Trimble receiver, and Trimble OCXO inside.[I
think it runs Lady Heather] What I would like to know is what uncertainty
the 10MHz output will be with a 10 second count.This presumes that the
GPSDO is receiving satellite signals, and the OCXO is being suitably
diciplined. Should I expect 1 part in 10E12?, 1 part in 10E10?. This device
gives superior performance to an OCXO barefoot - but how much better? Would
somebody in the group who knows the answer, please wax elequently.
Thankyou,.................................................................................................Donald
B. COLLIE
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ew via time-nuts
2018-10-08 19:52:51 UTC
Permalink
There are many issues with the Tbolt, specially if you look at 1 second and below. But at 10 seconds they mostly average out. If you look at the attachments first the 1pps varies by 20 nsec, has nothing to do with the Tbolt. It is GPS and the change in propagation from day to night of the ionosphere. Second Tbolt was intended as a timing device, frequency is secondary and is used to correct timing. Plot shows it is within 1 nsec short term. Nice
Even very good and expensive OCXOS like the OSA 8600 frequency at best is 2.3 E-12 at 1 second. Forget the 8607. Not talking ADEV. That is our design goal for a GPSDO.The frequency plot tells you that at 10 seconds it is safe to assume +-3E-11. The Tbolt has been in continuous operation for three years and I am fortunate to have an excellent antenna location. Strictly interested in Frequency and clean up with an Austron 2110. Not shown. Reference is a HP 5061B set to 2E-13.Hope this helpsBert Kehren
In a message dated 10/7/2018 10:00:38 PM Eastern Standard Time, ***@gmail.com writes:

I have a GPSDO which has a Trimble receiver, and Trimble OCXO inside.[Ithink it runs Lady Heather] What I would like to know is what uncertaintythe 10MHz output will be with a 10 second count.This presumes that theGPSDO is receiving satellite signals, and the OCXO is being suitablydiciplined. Should I expect 1 part in 10E12?, 1 part in 10E10?. This devicegives superior performance to an OCXO barefoot - but how much better? Wouldsomebody in the group who knows the answer, please wax elequently.Thankyou,.................................................................................................DonaldB. COLLIE_______________________________________________time-nuts mailing list -- time-***@lists.febo.comTo unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow the instructions there.
Tom Van Baak
2018-10-09 12:49:51 UTC
Permalink
Hi Don,

Thanks for the additional information. Ok, your GPSDO is clearly not a TBolt.

Can you confirm that your board is like this one: https://xdevs.com/fix/rb_lpfrs/#gpsdo

You might want to try using Heather on this GPSDO. That will assist you in seeing if it has good reception, and other parameters. It's an alternative to typing raw hp scpi commands (as seen in that web page).

As far as your 10 s gate time frequency accuracy question -- that's hard to answer without seeing Trimble specs for this board, or without doing actual measurement. There are many variables. Not all GPSDO are alike, not even close. But your 1e-10 guess is a good one. Still, we prefer to measure rather than to guess, when possible.

Has anyone on the list used a GPSDO like Don's? Are there specs? Has anyone done performance measurements?

Thanks,
/tvb

----- Original Message -----
From: donald collie
To: ***@leapsecond.com
Sent: Monday, October 08, 2018 6:07 PM
Subject: Re: Fw: GPSDO uncertainties


Thankyou to those who have replied so far. So it depends on the GPSDO itself. I didn`t know this. Mine is ex China, and has a Trimble PCB, with the receiver module, and Double [?] oven There`s another PCB, which is fabricated in China, and well made too, which has PSU`s and buffers for the sinusoidal output. I`ll go open it up now and make some notes... standby... The USA designed PCB is designated "TRIMBLE 57963-D". The oven is serial number : 468010-0114, and the date code is 0950 - presumably Jan 1995. The Trimble PCB has dimensions : 4 1/2'' x 2 3/4". I`m not sure how many satellites I can aquire this far south [I am below 45 degrees latitude here], but after 20 minutes or so, the data LED goes into high gear, so I reason I`ve aquired at least one. ;-). This little unit seems to outperform the OCXO`s in my 5245L, and 8566B, which are accurate to something like 1 part in 10E9, on a 10 second count, but I`m not sure how much it is outperforming this. Thankyou Bob, Bert, and Tom, for your replies.................................................................................................................................................................................................Donald Brett Collie ZL4GX


On Tue, Oct 9, 2018 at 10:12 AM Tom Van Baak <***@leapsecond.com> wrote:

Hi Donald,

Do you have the make/model of that GPSDO? Or some part numbers or a quick photo? Or anything more than just "Trimble receiver and Trimble OCXO". Otherwise I think people will post guesses instead of answers. Trimble only makes a few receivers so even the dimensions of the PCB might be enough that we can ID the part.

Thanks,
/tvb

----- Original Message -----
From: "donald collie" <***@gmail.com>
To: "Discussion of precise time and frequency measurement" <time-***@lists.febo.com>
Sent: Sunday, October 07, 2018 6:59 PM
Subject: [time-nuts] GPSDO uncertainties
Post by donald collie
I have a GPSDO which has a Trimble receiver, and Trimble OCXO inside.[I
think it runs Lady Heather] What I would like to know is what uncertainty
the 10MHz output will be with a 10 second count.This presumes that the
GPSDO is receiving satellite signals, and the OCXO is being suitably
diciplined. Should I expect 1 part in 10E12?, 1 part in 10E10?. This device
gives superior performance to an OCXO barefoot - but how much better? Would
somebody in the group who knows the answer, please wax elequently.
Thankyou,.................................................................................................Donald
B. COLLIE
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Mark Sims
2018-10-09 18:31:53 UTC
Permalink
I did some measurements on the Trimble using a TAPR TICC. The "PPS" adevs are the Trimble and the "OSC" adevs are an Oscilloquartz STAR-4.

http://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg1143960/#msg1143960

-------------------
Post by Tom Van Baak
Has anyone on the list used a GPSDO like Don's?
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donald collie
2018-10-11 01:52:53 UTC
Permalink
Nobody in this group could answer my question. Thankyou, nevertheless, to
all those who replied. Kind regards...Don Collie jnr ZL4GX
Post by Mark Sims
I did some measurements on the Trimble using a TAPR TICC. The "PPS"
adevs are the Trimble and the "OSC" adevs are an Oscilloquartz STAR-4.
http://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg1143960/#msg1143960
-------------------
Post by Tom Van Baak
Has anyone on the list used a GPSDO like Don's?
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