[time-nuts] GPS multipath

Jim Lux jimlux at earthlink.net
Sat Aug 9 13:02:54 EDT 2014


On 8/9/14, 9:33 AM, Magnus Danielson wrote:
> Jim,
>
> On 08/09/2014 05:31 PM, Jim Lux wrote:
>> Clarifying my previous question..
>> There's no doubt that multipath exists, and how to test is fairly
>> straightforward, whether with multiple antennas, cables, or waving
>> cookie sheets around..
>>
>>

>> Ultimately, the way to find out is just to get a GPS sampler, record
>> some raw bits, and then run the correlator and look for the second peak
>> from the reflection.
>
> Quite possible, but... outside of a chip period, the Gold-code will
> relatively effectively de-correlate multi-path, so it is only within the
> chip period that multi-path will affect things.
>

If you have a correlator process that gives you all the cross 
correlation bins, it's actually easier to see multipath that is greater 
than one chip away (e.g. 1 microsecond .. about 300 m, for C/A code)





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