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Re: [Discuss-gnuradio] Baseband GPS OTA USRP capture that anyone can sha
Re: [Discuss-gnuradio] Baseband GPS OTA USRP capture that anyone can share?
Fri, 25 May 2012 23:53:13 -0400
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This is the web page I was looking for.
I myself have never used RTKlib with an SDR.
Try to use a circularly polarized antenna.
GPS signals are circularly polarized to allow the antenna to have some
degree of rejection of signals reflected from the ground. The simplest
to make rhcp antenna for a single frequency, say 1575 MHz, is going to
be a helical antenna. If your right hand is the coil windings and your
thumb is facing up, the winding will go in the direction your fingers
point. There are calculators on the net.
(Note that the measurements they will give you are for an air core.)
If you want a *broadband* circularly polarized antenna, you might want
to look at spiral antennas like the "equiangular spiral" (logarithmic
spiral) antenna or Archimedes spiral. The two arm design works best with
a balun. There is also a very innovative design *that uses coax as the
balun*. Its cheap and could work over a 8:1 frequency range!
IMO, with that antenna, performance could be quite good plus it works
over a very wide frequency range. Google "infinite balun" or look at
this page and scroll down. The antenna I am talking about is the one
made out of a single piece of coax. That design does not look like it
would be a good antenna but actually it is an extremely good antenna for
satellite reception if you use the appropriate size for your frequency
and the appropriate polarization. And of course, you can make a single
antenna and simply flip it over to get the other polarization when you
You could also make a similar design using a PCB and a stripline instead
Most of the low cost GPS antennas you see are not very good. To really
take advantage of RTKlib you need a good antenna - good being defined as
one with minimal phase center variation and high rejection of opposite
polarized (reflection) signals. A vertical whip is going to be an
absolutely terrible GPS antenna.
I've mostly used RTKlib with a local non-SDR receiver and gotten
correction data from (as nearby as possible) RTCM data server, usually
post processing. I think that is a typical use pattern.
There are lots of servers for correction data. Some of them are free.
I don't know how to use RTKlib with an SDR but its definitely being
done. Look at the URL above to start. If you can't figure it out email
Tomji Takasu its author. He is into software defied radio, he would
probably be very helpful. Also, maybe there have been previous postings
on this here on this list?
On 5/25/12 11:35 AM, Andrew Davis wrote:
I didn't see that may 9th post. I could get some samples ( USRP with
rubber duck with clear sky, would that work? ).
Does anyone know how to feed RTKNAVI? What format does the file need to be?
On Fri, May 25, 2012 at 12:06 AM, Chris Beaumont<address@hidden> wrote:
A while ago (May 9) there was a post to the list about raw GPS data as
captured by a USRP.
These web pages may or may not be useful, I don't know if the data files on
the first one are the right format for you (they were not captured by a
USRP) but they may still be helpful.
If not, Michele might be able to help point you to where you could find data
Also, you should check out this web page:
Tomoji Takasu has done quite a bit of amazing stuff with GPS including SDR
development. (you may have to dig a bit for it but its there)
Between one or the other you should be able to find what you are looking
On Mon, 2011-05-09 at 10:27 -0500, John Andrews wrote:
Is there is anyone here who has GPS OTA capture using USRP that they
are willing to share? I don't have a USRP and I am interested in
demodulating the GPS signal.
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