GPS receiver with Raw Data Measurements

Hello Everyone!
I am trying to find a cheap GPS receiver, that will send to my
listening PC the actual measurements from the satellites
(phase measurements, pseudorange etc).
Specifically, i am interested in using the GPS measurements
to calculate my own GPS position.
I imagine a serial/usb device, that would send the data in ASCII
or smt format, so that i can easily utilize them
I tried to find something in the web, but i was able only to find
hack solutions (take a normal receiver, hack it down to isolate the signals,
connect them via a complicated hardware way to something in the PC)
Does anybody has something in mind?
Is there a product, i can plug in my PC, and have raw measurements on my screen?
MTIA
Grigoris Lionis

You might want to look at the sirf-III usb units. In theory they have
sentences for the raw data. Check out this pdf (and the other ones in
this directory). Warning, I haven't tried decoding the data so I
don't know if it is documented but not implemented or if it simply
doesn't work. I do remember thinking that I should really try to run
one of the open-source gps programs using this data.

http://www.usglobalsat.com/downloads/SiRF_Binary_Protocol.pdf

http://www.usglobalsat.com/item.asp?itemid=60

The BU-353 usb sirf-iii gps is under $80 mail order and it is a very
decent gps. It tends to do much better at locking in weak signals
than many $500+ handheld gps's. I expect it would have cleaner raw
data than many gps's too.


Nothing interesting is ever in ASCII. You will need to decode the
binary, but that is trivial. Unlike RTCM-SC104 and other insane
protocols, the gps binary formats the manufacturers come up with tend
to map onto C-structs very well.

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/

I have been doing all of the above with a Garmin GPS II+ and an ETREX
Legend, as well as the GPSMAP 72C. You will need to GOOGLE for Dennis
Milbert and check out "garbin" to log the data and "gl2rnx" for RINEX
conversion or you can check out Antonio Galan and get "async" to log the
data and "gar2rnx" to do the conversion to RINEX format. There is also a
package called Gringo the performs all of the logging and conversion.
You then need post-processing software to generate the accuracy you are
looking for. This is all explained in the above articles.
Have fun.
glion@mail.ntua.gr wrote:
screen?

trgraham wrote:
screen?

If you're willing to do some soldering, you should consider OEM
receiver boards. Both the Antaris ($119 from www.u-blox.com) and the
Thales AC12 ($149 from www.navtechgps.com) have very good carrier phase
data. These are raw circuit boards and you have to hook up your own USB
interface. It is pretty easy if you use one of the standard USB modules
($19 from www.sparkfun.com.) and a Radio Shack prototype board.

For a ready-to-go solution, look at the Antaris LEA-4T evaluation kit.
At $350 it is not inexpensive, but it is almost as sensitive as the
Sirf III and has quality measurements. At a more reasonable price, the
Sirf II and Garmin Gps18 provide raw measurements, though I hear they
are not as precise as the Antaris and AC12.

The Sirf III chip does NOT provide carrier phase. (bummer)

I've written software to talk to these various receivers, but things
aren't working well at the moment. You're welcome to look at what I
have so far at www.precision-gps.org. My work schedule is easing up, so
I may have a chance to get back to it.

- john