Warren,
WarrenS wrote:
If you needed to lower your AMU limit from 4 to 2, you are feeding the
Thunderbolt a signal level below the intended levels.
True, You MAY be feeding it a signal that is below what the cell site
recommended High gain outdoor antenna will give it.
But any conclusion past that sounds like pure speculation. And most of use are
not using them in cell sites.
True, but lowering this value should be a warning-sign that you may not
get the performance of the spec-sheet. There where some debate on wither
the signal level was an issue or not. Lowering the AMU limit only lowers
the acceptance level of signal strength for a sat in view to be accepted
for tracking. Regardless how AMU is cooked up (an issue we could ponder
over as a side-track), it remains a signal strength measure.
I Can not comment on the other units Magnus referred to that don't work if set too low,
and I can not say what AMU is in the Tbolt
BUT I can say with certainty that setting it to a value of 1 or 2 with 'Tboltmon.exe' version 1.2 works fine
and 1 works MUCH BETTER than 4 in some setup.
Looks like the Tbolt software is not so dumb as to use sat signals that will
screw it up.
It uses the AMU limit to select among the available sats. It then uses
the T-RAIM to cancel out any outliners among that subset of sats to
churn out which sats is being used for positioning/timing solution.
The AMU limit is nothing magic, it's only that we don't have a good
reference to what the AMU value is in detail, but we do know that high
values is good and low values is bad.
Lowering the AMU value as you did is good in the sense that you got more
sats to actively track. It is bad that the signal levels the Thunderbolt
is experience is so low that you need to take that action. Low signal
values means more timing noise and thus more timing instabilty. Having a
few sats is better than none.
So it is an indication that the unit would like some more gain... 10 dB
or so.
'Trimble GPS Monitor V1-2.pdf' instructions on page 13 shows the "signal
level mask (AMU) set to 0.6
If the statement that AMU is a linear scale is correct, that would mean
that the C/N limit is set 16,5 dB lower than normally, i.e. that C/N
being 16,5 dB lower can be accepted.
It would be fun to play around with a variable damper to see what
relationship to level the AMU value is on the Thunderbolt.
Cheers,
Magnus
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