[time-nuts] antennas was Re: Common-View GPS Network

Jim Lux jimlux at earthlink.net
Thu Apr 18 14:00:07 UTC 2013


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.






>




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