[time-nuts] Lucent RFTG Units

Jim Miller timenuts at jcmco.com
Tue Jan 30 16:43:25 EST 2007


On Jan 30, 2007, at 1:22 PM, Robert E. Martinson wrote:

> Hope everyone has not stopped experimenting with these nicely made,
> reasonably priced, units, but certainly the email regarding them  
> has fallen
> to almost zero these last few weeks.

I posted a few emails with the results of my reverse engineering but  
didn't get any
significant response so I haven't posted any more.  Investigation  
goes on however.

> They both power up, but
> both indicate "No GPS", and the XO also indicates "Fault", the RB unit
> indicates "ON".  I have the two J5 connectors interconnected per Jim
> Miller's email of 12/30/06 at 3:34pm, and the Ref In/Outs with an  
> SMA cable.

They should come out of "NO GPS" after 15-30 minutes.

> Even with the receiver plugged back into the XO unit,
> the data on the front panel J5-2 is clearly visible with  
> HyperTerminal &
> also Visual GPS is happy with this data.

Be careful not to load the interconnect lines down with probes or  
external
level changers. It is easy to knock one or both units into "FAULT" by
aggressively probing signals on the interconnect cable.

> Even after many hours the RFTG units continue to indicate "No GPS",  
> and the
> XO unit also shows "Fault".  I tried the XO unit by itself (no  
> connections
> to the RB unit) and the XO is still unable to obtain lock. I have been
> monitoring the crystal frequency (using a clip lead directly from the
> crystal) of the XO unit for 8 hours with an HP 5370B locked to my  
> HP Z3801A

Again, be careful of your probe loads.  I found this out the hard way  
- too many
loads (50Z on my 5370, freq counters on the oscillator, inverters on  
the serial lines
etc) will spoil your results. I recommend initially bringing the  
units up in their
original, as-designed configuration in order to establish a baseline.

As mentioned earlier, you should get GPS lock in 15-30 minutes.  Do  
you have a
good DC voltage on the TNC GPS antenna connector when the receiver is  
installed
in the RFTG?  The RFTG has its own DC injection circuitry.

> I see commands initially being sent to the GPS receiver (monitoring  
> its
> header pin 9 with an oscilloscope), however by simultaneously  
> monitoring the
> calculated position using VisualGPS, its obvious that the receiver  
> is not
> going into position hold mode.

It takes 12 hours or so to transition into position hold mode.  I use  
TAC32 for
monitoring the receiver and TAC32's "Receiver ID" screen will show  
the status
messages about the mode changes.

Have you been able to capture and decode the motorola binary messages
going from the CPU to the receiver during initialization?  This would  
be useful.

> Don't we have any helpful Lucent employees in the group?

I do not know about any Lucent employees in the group but it is very  
possible that
company policy is not to release documentation to the public - and  
those that do
have access to it might like their jobs more than they like the  
timenuts.

It is also possible that the only docs available are written at a  
high level and would
not be very useful in these pursuits.

73 de JIM N8ECI




More information about the time-nuts mailing list