[time-nuts] Thunderbolt reception problems

bg at lysator.liu.se bg at lysator.liu.se
Sun Nov 22 21:22:03 UTC 2009


Hi Nigel,

AMU and SNR are two different scales. I do not have a translation. A
Kepler award recepient once explained Trimbles AMU as "a meaningless
unit". That said, SNR or C/N0 values cannot be directly compared between
different receivers since the measures might be taken at different points
in the receiver.

The Trimble monitor program can be made to switch between AMU and SNR in
one of the configuration menues. I think you might have switched to SNR.

With above uncertanty of specific SNR definitions noted, most receivers
are enjoying an excellent signal if the highest elevation receivers have a
SNR above 50. If the highest SVs get +45dB that is still decent.

--

   Björn
>
> In a message dated 22/11/2009 19:45:35 GMT Standard Time, SAIDJACK at aol.com
> writes:
>
> 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.
>
>
> Hi Said
>
> Just out of interest, what levels of AMU are you seeing reported?
>
> According to Trimble's Thunderbolt Monitor version 2.6 the six satellites
> I'm tracking right now are showing AMU values of over 40 and another stops
> tracking when its AMU drops to approx 33 but starts tracking again at  a
> reported AMU of approx 36 to 37.
>
> My signal level mask is set to 4.0, and I don't seem to have  had any
> problems because of that, but I'm intrigued as to the actual  relationship
> between the quantity described as the signal level  mask and the reported
> AMU
> levels.
> I would have assumed the units to be the same but that doesn't seem to  be
> the case.
>
> OK, so I've just dropped the threshold to 2.0 and am now tracking eight
> satellites, with the reported levels for the one mentioned above still
> varying
>  as before and another just below  30 with neither dropping out, but I'm
> still non the wiser as  to the actual value of the set threshold in terms
> of
> the reported AMU  levels.
>
> regards
>
> Nigel
> GM8PZR
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