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Old March 3rd 16, 06:43 PM posted to rec.radio.amateur.antenna
Jeff Liebermann[_2_] Jeff Liebermann[_2_] is offline
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Default Inmarsat L band Antenna problem

On Thu, 3 Mar 2016 16:28:07 +0000, Jeff wrote:

To me what you have seems like a bit of an odd antenna setup. For it to
work well the LPD active section at the Inmarsat frequency will have to
be at focus of the dish, which is mechanically difficult. You may be
better of looking for either a different antenna completely, or using a
circularly polarized feed for the dish (which may be a bit too small for
the frequencies involved anyway).

Jeff


Oh, I didn't see the part about the dish. Since the size of the dish
isn't specified, it's difficult to determine if it will work. For
example, if the dish were a common Ku band DBS dish, it is too small
and will not have much gain at 1.5GHz[1]. If it's a converted kitchen
wok, as is common in wi-fi circles, it's also probably too small and
insufficiently close to a parabolic surface. If the dish is a
converted C-band dish, it will probably be very difficult to aim as
the beamwidth can be extremely narrow.


[1] I ran the numbers for a DBS dish at cellular frequencies a few
years ago:
https://groups.google.com/forum/?hl=en#!original/alt.internet.wireless/7KUW6sGRXls/hhS4ZsRouwUJ
Plug in 1500MHz instead of 850/1900MHz to see what theoretically can
be done with a DBS dish assuming everything else is perfect. My guess
is you'll do about the same as a single CP patch antenna (about
10dBi).


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Jeff Liebermann
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