[time-nuts] Carrier phase tracking
cfmd at bredband.net
Mon Feb 19 17:44:04 EST 2007
From: Hal Murray <hmurray at megapathdsl.net>
Subject: Re: [time-nuts] Carrier phase tracking
Date: Mon, 19 Feb 2007 12:34:33 -0800
Message-ID: <20070219203435.19DB9BE07 at ip-64-139-1-69.sjc.megapath.net>
> > But... as marketing people thinks that 'more satellites, better' some
> > manufactures are commercializing small GPS receivers with 16 and even
> > 20 channels... and obviously, no advantage over 12-channel ones.
> > Perhaps they expect the Navstar constellation to be so crowded in the
> > near future to don't let the Sun rays reach the Earth :-)
> How many satellites are there in the Russian or European systems?
GPS: 31 sats
GLONASS: 13 sats
GALILEO: 0 sats (but they have a test-sat)
Those numbers are from the CODE tracking, but they track sats being taken out
of active constellation, so more real numbers comes from more official sources:
GPS: 30 active sats (SVN15/PRN15 is taken out)
GLONASS: 14 active sats
GALILEO: 0 active sats.
> Or will there be if/when everything gets fully deployed?
GPS: 32 (?) sats (sats lasting longer, published codes running out, etc.)
GLONASS: 24 sats @ 2010
GALILEO: 27 sats
> How close are the frequencies?
Traditional GPS and traditional GLONASS have separated footprints, but close
enought for common solutions. Modern GPS and GALILEO share foot-print but
GALILEO has additional frequencies. Modern GLONASS adds another frequency.
> What's the bandwidth of the signal?
It is a matter of traditional to modernized and upcomming. 2,046 MHz for
traditional GPS C/A code, but it actually extends to 20,46 MHz and you can get
additional benefits for accepting a larger window at the cost of reduced
jamming suppression. The benefit being better multipath performance.
> How far does doppler shift things?
GPS-L1 you can see shifts like 6-7 kHz on the L1 carrier.
> Is there spectrum set aside for this use, or is it shared with other
> applications and the receiver has to dig the signal out of a mess that's
> worse than just noise?
The spectrum is set aside, but there have been attempts to make use of it
from several directions, UWB is only one.
There is a hole in the middle set aside from radioastronomers, who don't like
the L3 transmissions.
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