[time-nuts] World's most precise.... wall clock

[Tom Van Baak]

 > In tboltmon, the signal "strength" indications are displayed in units
 > called 'AMU' for which I've been unable to find a definition.

Amplitude Measurement Units? There was a discussion about this some 
years ago. The TBolt (and other Trimble receivers) give a user the 
choice of reported GPS signal level in either AMU or dBc units. Mark 
Sims (Heather author) collected data using both units to create a 
cross-reference. I've attached his data (file: 
2010-Sims-TBolt-AMU-dBc.zip).

His reply from 2010 is here:

 > From: "Mark Sims" <holrum at hotmail.com>
 > To: <time-nuts at febo.com>
 > Sent: Saturday, February 13, 2010 8:48 AM
 > Subject: [time-nuts] Thunderbolt AMU to dBc conversion
 >
 > The data was collected in 0.1 dB / AMU steps. There was a lot of noise
 > in the raw data (maybe ± 1 dB or AMU), but the general trend of the
 > curve was quite distinct. I smoothed it out by hand and filled in a few
 > (maybe 15) of the missing steps that had no signal.
 >
 > The 0.1 resolution of the raw data causes the piecewise linear steps in
 > the data. I was going to run a smoothing filter over it, but the curve
 > is pretty good as-is (especially considering how it was generated).
 >
 > Heather now uses a table lookup from 0.0 to 25.5 AMU with a linear
 > approximation over 25.5 AMU to convert AMU values to dBc values when
 > drawing the signal level map if the receiver is in AMU mode. The plots
 > collected in AMU mode and dBc mode are virtually indistinguishable
 > (within the normal variation seen between two different runs in dBc 
mode).

The entire thread is worth reading from the archives. [1] [2]

See also table 7.3 on page 124 of:

ftp://geodesy.noaa.gov/pub/abilich/papers/ABilichThesis.pdf

/tvb

[1] https://www.febo.com/pipermail/time-nuts/2010-February/044968.html

[2] 
http://lists.febo.com/pipermail/time-nuts_lists.febo.com/2010-February/027397.html

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