[time-nuts] Thunderbolt reception problems

[SAIDJACK at aol.com]

Hi guys,
 
some weeks ago we talked about reception problems on Trimble Thunderbolt  
units. I finally took the time to download the Trimble monitor again, and get 
my  unit locked again. Here is what I found:
 
The unit was running continuously for the last months, but wasn't  locked. 
Using the Trimble monitor, I restarted the unit, now connected  directly to 
my antenna, then after the survey was done let it run from my  antenna 
splitter.

This works, but just barely. I use an Agilent 58512A amp, followed by a  
Mini Circuits ZB4PD1-152-75+ 1-to-4 passive splitter.
 
In the attached plot a JLT FireFly-IIA and the Thunderbolt are both running 
 from the same Mini Circuits splitter. The Antenna sense circuit in the  
Thunderbolt is happy, but the signal strength is just at the threshold of  
working. The Sats kick in and out. Please see the attached screen  shot.
 
At the same time the FireFly-IIA receiver is tracking 11 Sats with perfect  
signal strengths (up to 45dB+ C/No), from the same feed.
 
The difference in receiver performance is quite clear. Unfortunately I  
have only a single antenna, so need to run the Thunderbolt from a  splitter.
 
One can also see two more interesting tid-bits in the screen shot: the  
FireFly-IIA is tracking and using WAAS Sat PRN 48 (PRN 51 goes in and out of  lo
ck due to a chimney being in the way), and it is showing true MSL rather 
than  just GPS Height.
 
Thanks for the help,
bye,
Said

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