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

[Magnus Danielson]

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.

Cheers,
Magnus