[time-nuts] Re: Measuring oscillators against GPS - Trimble NetRS

[paul swed]

Tom
Been following the thread with interest. I think several years ago it was
mentioned that LadyHeather could produce results by using a external 10 MHz
into a GPS reciver for its main oscillator. Always seemed like a great just
over the horizon project.
With respect to the uBlox F9. Lost me on that part. I think your suggesting
to obtain the sawtooth? It will not take in an external 10 MHz.
Thanks for you thoughts.
Paul
WB8TSL

On Mon, Mar 7, 2022 at 6:57 PM Tom Wallace <thomas.h.wallace at gmail.com>
wrote:

> I've been using the NetRS for timing for a couple of years now. They are
> inexpensive and work well when properly configured, but they do have
> their quirks. Some notes I've found useful:
>
> 1. The NetRS needs a dongle to provide primary power and the Ethernet
> interface. Approximately 100% of the ex-USCG receivers on the well-known
> auction site come without the dongle, so plan to locate one elsewhere or
> build one (pinouts are in the manual).
>
> 2. UNAVCO's resource page on the NetRS
> (https://kb.unavco.org/kb/article/trimble-netrs-resource-page-471.html)
> is a trove of useful information (manuals, FAQ, etc.) If that page
> didn't exist, it would be a major undertaking to get a NetRS working well.
>
> 3. The latest firmware (1.3.2) is available from UNAVCO
> (https://kb.unavco.org/kb/article.php?id=770). It adds the ability to
> receive the L2C signal in addition to the L2P(Y), and corrects some
> security vulnerabilities. It can be applied no matter what the unit's
> warranty status (all the surplus ones are out of warranty).
>
> 4. For timing use, clock steering on the NetRS must be turned off.
> Otherwise, the clock values are smeared by the steering and don't
> reflect the state of the 10 MHz input.
>
> 5. Converting the binary output of the NetRS to RINEX is a multistep
> process: use runpkr
> (
> https://kb.unavco.org/kb/article/trimble-runpkr00-latest-versions-744.html)
>
> to convert to .tgd format, then teqc
> (https://www.unavco.org/software/data-processing/teqc/teqc.html) to
> convert to RINEX.
>
> 6. Computing clock stability from PPP data can be done over the net
> using NRCan (https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php)
> or locally using gLAB (https://gage.upc.edu/gLAB/). Comparison of these
> results gives good agreement (~1 ns) in the magnitude of the clock
> variations.
>
> 7. The absolute offset of a clock from the reference source is not
> easily determined using the NetRS; there is no consistency in the clock
> offsets computed by 2 NetRS systems using the same antenna and fed by
> the same 10 MHz reference. Interestingly, the differences are not even
> the same modulo 100 ns (the period of the 10 MHz signal).
>
> 8. The NetRS handled the last WNRO with no problem. However, I have been
> unable to find information on whether the system uses a pivot point to
> handle WNRO. If it does, and the pivot is the date of the last software
> release (October 2012), then the systems are good for another decade.
> However, I have no information on this, and would be interested to hear
> from anyone who does.
>
> 9. The sawtooth in the NetRS PPS output is very large (+/- 30 ns), and
> the output voltage is over 5V (it may have been designed to deliver 5V
> into 50 Ohms). If you want to discipline the oscillator you're
> measuring, I'd suggest checking the input level it can tolerate, or
> using a modern receiver like the uBlox F9 (which has around 1/8 the
> sawtooth variation).
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