[time-nuts] Anyone using Silicon Forrest's LPRO-GPSDO?

[David McClain]

I have an LPRO-GPSDO from Silicon Forrest. I just got a Trimble Tbolt  
to check against the Rb clock. As far as I can tell, by this  
comparison, watching beats of 3rd harmonics of the two clocks on a  
radio in AM-detection mode to keep receiver instabilities out of the  
equation, the Rb clock is within spec, showing about 50-80e-12 while  
disconnected from GPS, after first having been trained on GPS for 48+  
hours.

Trouble is... the idiot-light on the LPRO just doesn't make any  
sense, as per what the manual states. While disconnected from GPS the  
unit will variously show solid green -- locked to GPS with < 5e-11,  
flashing green with <1e-10, and red-green flashing (not toggling)  
with < 1e-8 (??). My measurements show a pretty good stability -  
better than Tbolt by at least a factor of 3-10.

Until I got the Tbolt, I had no idea what the LPRO was doing, nor  
where it was. The light indicators were so at odds with the manual,  
and the unit wouldn't maintain GPS lock for more than an hour at a  
time, that the guy at Silicon Forrest thought I might have an  
unstable LPRO and he sent another LPRO to try. The second unit was  
even worse -- worse in the sense that it would never indicate lock to  
GPS with the antenna connected.

This first LPRO does achieve lock to GPS, but seems only able to hold  
(as per solid green light) for around 1 hour before entering red- 
green toggling, all the while being connected to the GPS antenna. The  
only way to exit that red-green alternation state is to disconnect  
the GPS antenna for a few minutes, allow the unit to realize it has  
been disconnected as it signals flashing red/green, and then  
reconnecting the GPS antenna. Within a few minutes it becomes solid  
green again for another hour. Repeat ad infinitum...

So... I strongly suspect that the manual is completely incorrect. My  
LPRO sometimes drifts into solid green while the GPS antenna isn't  
even connected. How in the world could the unit know it is <5e-11  
when GPS isn't even connected? Or else, the little circuit plugged  
into the LPRO pins is whacked...

Does anyone else have this unit? and if so how has your experience  
with it been?

In my original total ignorance on this subject, I thought that by  
buying the LPRO-GPSDO I would have a plug-and-play solution. How  
little I knew... Now I wish I just had a plain vanilla Rb with a BNC  
on the front. I'd rather live without GPSDO on the Rb and just track  
its performance over time. For that reason I just ordered a Stanford  
PRS10 so that I could do PPS time tagging to keep a watch on the Rb.

Dr. David McClain
Chief Technical Officer
Refined Audiometrics Laboratory
4391 N. Camino Ferreo
Tucson, AZ  85750

email: dbm at refined-audiometrics.com
phone: 1.520.390.3995
web: http://refined-audiometrics.com