[time-nuts] Speaking of Costas loops

Magnus Danielson magnus at rubidium.dyndns.org
Thu Jul 4 21:19:57 UTC 2013


On 07/03/2013 11:59 AM, Attila Kinali wrote:
> On Tue, 2 Jul 2013 17:06:47 -0400
> <jmfranke at cox.net>  wrote:
>
>> Valid concerns all. What I am building is a squaring circuit for
>> recovering the carrier from a WAAS GPS satellite. Granted there
>> is still some Doppler and other issues, but the accuracy would not
>> be bad and it just looks like a fun thing to do. Plus, I can use my
>> four foot diameter dish antenna to reduce the number of satellites seen,
>> reduce thermal ground noise, and get some signal gain.
>
> Right.. i didnt think about the WAAS/EGNOS satelites.
> If i'm not mistaken, then you dont have to correct for doppler, as
> the satelites are stationary relative to you. The only thing you might
> want to correct for are atmospheric changes, but if you are tracking
> frequency only, and don't care about the phase relation, respektively
> can live with some phase noise, then you dont even need to do that.
>
> Correcting for atmospheric changes should be "fairly" simple. You just
> need to decode the WAAS/EGNOS signal, read the atmosphere/TEC data out
> and apply a phase shift according to that.

You still have doppler on WAAS/EGNOS since the orbit isn't really 
perfect, but it is less than for normal GPS birds.

You would need a pretty good directivity such that not nearby WAAS/EGNOS 
polutes the squaring. Using code (pretty simple) would allow to surpress 
nearby birds for cleaner result.

Cheers,
Magnus



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