[time-nuts] Thunderbolt reception problems

[WarrenS]

Said

>changing the AMU thresholds to 2.0 fixed the problem,
If 3 was not working, you should be able to go lower than 2, likely 1.0 to 1.5  will be better yet.
The way I tell is using Lady Heather,  if there are satellites signals with levels between 20 and 30 dBc 
with good ACCUs that are still not being used, I lower the AMU value using Tboltmon.exe.

> how much performance degradation will I get when using 2.0 as the AMU threshold rather than the factory default. 
Here is what I have found, concerning that question.  
Lowering the AMU will likely improve the noise performance of the typical setup,  
for some less than oblivious reasons concerning how the Tbolt reacts in holdover mode 
and when satellites are switched in and out due to their signal level. 
Much better to use a weak signal than have no signal AND 
also better not to toggle a satellite in and out  that is on the threshold, 
Better to lower the AMU threshold and rise the elevation mask.

Concerning the relation of AMU to dBc, what I've seen is: 
AMU of 4  is in the high 30, AMU of 3  is in the mid 30, AMU of 2 is in the high 20, AMU of 1  is in the mid 20, 
A good outdoor antenna will give dBc in the high 40 to 50s
and poor indoor antena will give dBc in the mid 30's AND still works fine,
and anything above 25 dBc works OK when in the fixed position 'Overdetermined Clock' mode. 


To the different question of how much will the performance be degraded using a weak antenna signal,
Again the not so oblivious answer is typically only a little,  and may even help in some cases.
Weak  signals need the TC to be set higher than the default 100 sec, OR performance will be degraded.
The added signal noise needs to be averaged over a longer time period.

My experience is that using a standard 'car' antenna indoors, 
with a properly set TC, Damping and Dac_Gain will out perform a unit on a good view outdoor antenna 
IF that Tbolt is still set to the default settings, which most seem to be.  
The difference I see when Both are set up correct is around 25%.

The bottom line is that a good signal AND an accurate location,
 IS required to get the VERY BEST performance from a Tbolt, 
BUT there are MANY other things that have MUCH more effect that are often overlooked.

ws
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Hi Guys,
 
changing the AMU thresholds to 2.0 as suggested by Warren fixed the  
problem, the unit is now working properly, thanks much for the hint. And no,  this 
was not obvious to me.
 
It is always great to get constructive help rather than the "you should  
know better" type of comments.
 
In the end, it looks like this turned out to be a configuration issue  
rather than a receiver sensitivity issue. But this also begs the question: how  
much performance degradation will I get when using 2.0 as the AMU threshold  
rather than the factory default. There must have been a reason why Trimble 
set  the default so high, they mention something about multipath rejection 
in the  manual.
 
Why do I want to get this unit up and running: this unit has been  tested 
to have very good phase noise performance. I'll use  anyone's low noise 
source anyday.
 
bye,
Said