[time-nuts] GPS backup for the stationary time and frequencyuser

Magnus Danielson magnus at rubidium.dyndns.org
Fri Oct 8 08:48:44 UTC 2010


On 10/08/2010 03:35 AM, jmfranke wrote:
> When I said the feed would work, I was meaning it would work if LHC.
> The illustrations and text imply you could just place a normal GPS
> receiver at the feed location, but the polarization would be wrong.

Which was what I reacted on...

I am by no means a practical antenna expert, and the EM-theory is a bit 
fuzzy on the edges, but I do distinctly recall that signal is RHC and 
reflections becomes LHC so an antenna with RHC orientation will provide 
some first-degree damping of the LHC reflections. For this antenna setup 
the intended RHC signal is reflected and should become LHC... just as 
the interference... so it relies on the antenna gain of the dish to 
out-perform the other reflections for the half-space receiver that a 
normal GPS antenna is. The choke ring for a dish head has a distinct 
different pattern (forming an inner cone rather than flat space).

So, a normal antenna would kind of work since the antenna gain would 
overcome the poor LHC supression of a simple RHC antenna... yay.

If an LHC antenna was used instead... now we are talking.

Cheers,
Magnus




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