[time-nuts] Lucent RFTG-m-RB steered by Odetics GPStar

Guido Kueppers guikueppers at t-online.de
Fri Feb 11 19:21:23 UTC 2011


Hello and greetings to the list,

I'm a new member and would like to report on my efforts in controlling
the rubidium oscillator in the Lucent RFTG-m-RB module. I've been
sifting through the time-nuts archives but haven't found any success
stories on this apart from the original setup consisting of RFTG-m-RB
and RFTG-m-XO. So maybe my experiences are of interest to those with a
standalone RFTG-m-RB.
   In short, it seems to be possible to discipline the oscillator inside
the module if pps signal and accompanying time tags are applied to
socket J5. The pps should be of TTL level and the time tags must be of
the form of the Motorola Oncore "@@Ea..." message. This message is
described in the Oncore manuals so I won't go into it here. The time
tags must go to pin 4 and the pps to pin 9 on J5. 
   In a first approach, the pps was taken from an Odetics GPStar "time
and frequency system" and the time tags were provided  by a program
running on a PC with a sufficiently accurate clock and piped out through
the RS232 interface and a level converter. 
   A few minutes after signals were applied, the "NO GPS" led went off,
which I took for a hint that the setup wasn't completely idiotic. Also,
pps signals from the RFTG-m-RB and the Odetics, which previously were
apart several milliseconds, now followed each other by a 100 or so
nanoseconds.
  Next I flashed a microcontroller board I had lying around, to poll the
Odetics receiver for the necessary timing information and send it in
Oncore message format to the Lucent module. The pps pulse from the
Odetics receiver and a 10 KHz pulse train derived from the 10 MHz "REF
OUT" were then observed on a TEK 2440 for several days. 
   While before I applied the gps timing signals to the RFTG-m-RB, the
10 KHz pulses used to advance about 1.6 microseconds per day with
respect to the Odetics pps, they now essentially stay where they are,
apart for a wander of +/- 2oo nanoseconds during the course of a day.
I would like to believe that this is an indication that the rubidium
oscillator's frequency is indeed governed by the gps timing information.
I'm now waiting for an Oncore UT+ receiver to arrive from China and will
repeat the experiment with the original receiver.

On the subject of the Odetics GPStar "time and frequency system",  I
think I've seen a thread on this list last month where someone had
several of them and was about to take them apart. I would like to buy
one of those if possible. 
   Also, I might be able to provide a bit of information on the
programming interface as well as the the required antenna if someone is
interested. 

Best regards
Guido Kueppers




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