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

[Bill Janssen]

Magnus Danielson wrote:
> 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
So a dish reflector and a sub reflector and the GPS receiver at the dish 
would work? What is that
configuration called? I can't remember at this early hour.


Bill K7NOM