[time-nuts] GPS backup for the stationary time and frequencyuser
jmfranke at cox.net
Fri Oct 8 16:17:27 UTC 2010
Yep, a Cassegrain antenna would work.
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
> 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.
> 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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