Magnus, Jim, > On 04/18/2013 04:00 PM, Jim Lux wrote: >> On 4/18/13 12:01 AM, Chris Albertson wrote: >>> If I read the paper correctly you can skip the choke ring if you mount >>> the >>> antenna on top of a 2 meter or longer mast. Iron pipe comes on 10 foot >>> lengths. The choke ring is for portable survey antenna that can't be >>> placed on tall rooftop masts. I think a 2 meter pole on a roof pretty >>> much meets their criteria of multi path difference being over 10 >>> meters. >> >> >> >> yes.. multipath that is more than a chip away is generally filtered out >> by the PN tracking loop, so all you really worry about is multipath >> signals within a chip. For C/A code at 1 Mchip/sec, the chips are 300 >> meters long. If you're doing P/Y code, it's a tenth of that. >> >> In reality, if the multipath signal is lower, and it's "far" away (a >> good fraction of a chip) it doesn't contribute much to the output of the >> correlator. So their 10 meter thing is probably a good number for a >> "typical" receiver they make. > > It's an interesting mix of sample-rate/bandwidth, code you track and > distance between early-late detectors (normal distance is one chip) > comes in when analyzing and combat the multi-path. I recall there is > some subtle points with some of the C/A codes.
All of the "high quality" GNSS receiver manufacturers have their own version of correlator that try to mitigate multipath. See for example this Ashtech-document (for a ca 10 year old L1 only receiver (DG14/16)). ftp://ftp.ashtech.com/OEM,%20Sensor%20&%20ADU/DG16%20&%20DG14/Reference%20Material/Correlator.doc /Björn _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
