[time-nuts] Thunderbolt reception problems

SAIDJACK at aol.com SAIDJACK at aol.com
Sun Nov 22 19:44:56 UTC 2009


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
 
 
In a message dated 11/22/2009 07:06:00 Pacific Standard Time,  mag
nus at rubidium.dyndns.org writes:

If you  already moved the signal towards the lower end of the input 
sensitivity  range, then adding additional loss is an issue. GPS 
receivers degrade  their performance gracefully with lower input signal 
to the point where it  degrades more and more ungracefully. It's one of 
the tests that one should  do.

I have come to realize that my rig suffers severly from cable-loss  and 
the lack of antenna gain to be followed by a passive splitter before  it 
hits an active splitter. I had to build a gain-rig to overcome part of  
that, but it doesn't feel right to use two LNAs in series. It's just  
darkness before my eyes but it works.

The first fix to this is an  inline amplifier to be inserted at the 
antenna. Another fix would be to  use a better antenna  cable.

Cheers,
Magnus




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