[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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