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Re: Satellites show up multiple times

From: Greg Troxel
Subject: Re: Satellites show up multiple times
Date: Tue, 04 Aug 2020 11:53:10 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (berkeley-unix)

Andreas B <> writes:

> I'm using a ublox ZED-F9P with default settings, which works great.
> Some satellites have two entries in the seen/used list in cgps. In
> this case, a number is appended to the constellation abbreviation for
> the second entry (see e.g. below). In xgps, no number is appended.
> When the satellite shows up two (or more?) times in the list, does
> this refer to the receiver using several frequencies from the
> satellite (L1, L2,L5)?

Probably.  And probably the entire scheme of passing this from receiving
to display could use a good going over and some thought.  Dual-frequency
receivers have only recently become affordable at the hobbyist level.

> The SNR difference between the two entries of PRN 7 is 11, which
> really seems to be alot. Why this big difference?

could be differences in
  tx antenna
  tx power
  rx antenna
  rx local noise
  rx preamp noise figure
  rx preamp gain
  rx cable loss  
  rx noise figure

and surely other things I am not thinking of.  So I do not have an
expectation that C/N0 will match, and I don't have an expectation that
it will not.  Best to chase the signal path to make sure it all makes
sense, first.

Arguably a "where are the satelllites" list should not have multiple
entries but a "how am I receiving it" list should.  I find "3" strange,
vs something like L1/L2.  Keep in mind that Galileo has E5a and E5b.  So
there really needs to be a "signal" field added.

I think I am just talking about improvements that nobody has gotten
around to, so far.

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