On 07/03/2013 11:59 AM, Attila Kinali wrote:
On Tue, 2 Jul 2013 17:06:47 -0400
<[email protected]> 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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