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Re: [Discuss-gnuradio] Query on GPS

From: Robert W McGwier
Subject: Re: [Discuss-gnuradio] Query on GPS
Date: Mon, 21 Mar 2005 10:05:10 -0500
User-agent: Mozilla Thunderbird 1.0 (X11/20041206)

I will be supporting both endeavors personally in the sense that I want the
wideband front end for various purposes and will just use filtering to
narrow its response.  If necessary, I will lower its noise temperature and
filter in the same unit to make it work for GPS.   I am interested in using
the idealized front end as well.

When the wide band front end specs become available, I will decide if the
link budget calculations using that front end support 12 channel GPS
and if the filter or LNA/filter are required.

(The following contains funny looking ID tags, these are all amateur
radio callsigns).

On the GPS and GLONASS:  my friend Matjaz Vidmar,  formerly,
YT3MV, now S53MV, did a joint GPS, GLONASS   receiver
using a 68010 over a decade ago.  It was not a 12 channel receiver
but did 4 channel acquistion on either constellation and solved for
location.  We have moved on but that sets a bar I would like to
be able to jump over with this receiver.  My goal would be to use two
ports for GPS and two ports for GLONASS if all of that can be
shoe-horned into the FPGA.  The same techniques, with different
parameters, will be in use for both.  For both, the use of separated
antennas and differential correction all over the place should make
this one terrific geolocation receiver if we can shoe horn it all in.
The implications of this paragraph are that I want to use all four
receiver ports.  Two for GPS and if we can shoe-horn everything
into the FPGA, two for GLONASS.   The natural first step will be
the N-channel GPS receiver using one port.

Matjaz ,Jose' Machao (from Argentina), and I  lived in and worked
in (literally) the Microsat -AMSAT-NA labs in Gunbarrel, Co. when
the first four Microsat were built.  At that time, Matjaz worked for Jan
King in a job and we all worked for Jan King as slave labor.  Matjaz
was also in school at CU.


David Bengtson wrote:

My current thought's on a GPS front end is to make it GPS specific, as there are Receiver's on a chip that take care of the details' of downconversion, filtering, etc. The downside is that it's pretty single purpose, and doesn't really support anything else. In other words, no wideband front end on this. If I recall, Matt Ettus was talking about a wideband RF front end for the USRP.


Robert McGwier wrote:

We can do this I am sure.  I thank Dave and Krys for the advance
work they have been doing when not many (any?) were "listening".
If we allow the FPGA to do (carrier phase/code) (acquisition/tracking )
in a joint-detection process run on the FPGA, I believe we can do a 12
channel receiver.

In addition to this,  Brickle and I have specific interests in
Cognitive Radio usage of the USRP as a wideband front end and
likely hooking this in to a system with a narrow band SDR to
prosecute the signal in a higher dynamic range regime.  We are
extremely interested in active antenna work as well.  I would
like to be doing four channel beam steering by the time of
AMSAT-NA symposium this fall. Bob

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