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

[jmfranke]

Yep, a Cassegrain antenna would work.

John  WA4WDL

--------------------------------------------------
From: "Bill Janssen" <billj at ieee.org>
Sent: Friday, October 08, 2010 11:52 AM
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Subject: Re: [time-nuts] GPS backup for the stationary time and 
frequencyuser

> 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
>
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