[IGSMAIL-5795]: Leica GRX1200GG Pro with external freq standard

[Jim.Ray]

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IGS Electronic Mail      17 Jul 12:29:02 PDT 2008      Message Number 5795
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Author: Jim Ray

While the Leica GRX1200GG Pro receiver is nominally
equipped to accept an external frequency standard, it
is not obvious how to get the receiver to actually
slave the internal oscillator to the external signal.
Within the IGS network, the following stations are
reported to have such a configuration:
   DARW -- Rubidium
   WROC -- Rubidium
   WTZR -- H-maser

However, in all cases the observed station clock
performance is consistent with an internal crystal
(steered to GPS time).  This can be seen, for instance,
in the plots posted at:
   https://goby.nrl.navy.mil/IGStime/filelisting.php?D1=IGST&D2=1486
for wk 1486.

After a lengthy investigation working with personnel
at the U.S. Naval Observatory and Leica, my colleague
Ernie Marion has developed the following procedure,
which seems to work in local tests.

* Importantly, the Leica GRX1200GG Pro does not support
control of the external oscillator directly via the web
interface.  This function must be addressed using the
Leica "RX controller" device connected directly to the
receiver, on site.  If you do not have an RX controller,
please contact Leica.

* When using the RX controller, there is an option "user"
in the external oscillator settings which must be used.
See the image posted at:
   http://www.ngs.noaa.gov/igsacc/WWW/misc/leica-RX-controller.jpg

* From here, you must enter the appropriate clock
parameters. The necessary information should be known
based on the technical specs for the external clock
device in use.

* To ensure that the external signal locks properly,
switch from the 5 Mhz setting (if that is correct for the
clock in use) to 10 Mhz.  Let it save that setting, then
watch to see that the receiver unlocks.  Once it is unlocked,
switch it back to 5 Mhz, and then it should lock again.

* Then you can test this by removing the frequency reference
cable.  If it unlocks, that's good. Put the cable back, it
should lock again. Then you are good to go!

But it would be best to verify proper operation by later
checking the IGS clock plots at the NRL website above.

A similar procedure can be used if a 1 pps input signal
is supplied (ordinarily only for time transfer operations).
Just cycle the setting back and forth a few times to make
sure of the correct setting.

I very much appreciate the diligence of Ernie and his
collaborators in resolving this issue.