[teqc] MultiPath with L1 GPS receiver

Hannan Sadar hannan.sadar at gmail.com
Thu Feb 3 18:17:54 MST 2005


Thanks for the fast replay.

I did not understand the last part of Jim's answer:
"I think you will find quite a bit of multipath with long wavelengths
(2-5 min), especially if you are using a cheap patch antenna."

The wavelengths is a fix to ~0.19m. I would be glad if you could
elaborate about this.

Thanks

Hannan


On Thu, 3 Feb 2005 18:06:51 -0700, James Johnson <jjohnson at ucar.edu> wrote:
> Dear Hannan,
> 
> Teqc requires dual frequency data in order to a multipath estimate.
> This is because teqc looks at a long term difference between the phase
> and code measurements while removing the ionosphere.  In principle, you
> can do this with single frequency data over a short period of time, but
> after some time the L1 phase and C/A measurements will diverge due to
> the ionosphere (phase advance on L1 and group delay on C/A).  What you
> want to look at is a running average of C/A - L1*lambda where C/A is
> the pseudo range measurement, L1 is the phase measurement in cycles,
> and lambda is the wavelength of L1.  If you use a running average of a
> 10 min, you should be able to see the multipath signal, an you could
> look at the RMS of this value (with steps removed caused by possible
> cycle slips).  Unfortunately teqc does not do this.
> 
> I think you will find quite a bit of multipath with long wavelengths
> (2-5 min), especially if you are using a cheap patch antenna.
> 
> Hope this helps,
> -Jim
> 
> On Feb 3, 2005, at 5:53 PM, Hannan Sadar wrote:
> 
> > Hi,
> >
> > I have what is consider low cost GPS receiver and i would like to find
> > the multipath i was having on my measurements. I have psuedorange,
> > phase and Doppler of L1. I would to know if teqc could find the
> > multipath on of the measurements of teqc needs P1 data to do some
> > averaging if I remember correctly.
> >
> > Thanks
> >
> > Hannan
> > _______________________________________________
> > teqc mailing list
> > teqc at ls.unavco.org
> > http://ls.unavco.org/mailman/listinfo/teqc
> 
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