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Re: BBQ Dish Gain

on 3/8/03 4:34 AM, Edward R. Cole at al7eb@ptialaska.net wrote:

> The 3 dB penalty of using linear polarization on AO-40 is considered a loss
> rather than an dish efficiency parameter but the result is the same.  The
> LP BBQ dish will be the equivalent of using a smaller CP dish.  My guess is
> that 24 dBi is about right for the BBQ dish gain and it performs like a 21
> dBic gain CP dish.

Agreed.  Eric, the 24 dBi number that is bantied about is from the
manufacturer's specifications.  I went to Trans-System's web page
(www.transystem.com.tw) and found the antenna listed with that spec.  Is it
dubious?  I'd say it's definitely on the optimistic side of things.

As for the effect of CP, it's tough to intuitively say that the gain goes
down, but in a sense it does.  You are trying to receive a signal half of
which is outside the receiving plane of the antenna.  Think of it this way,
if I have a horizontally mounted terrestrial beam that has say, 12 dB of
gain at UHF, it always has 12 dB gain at UHF in the plane of the antenna.
If I try to receive a vertically polarized signal, it doesn't have any gain
in that plane of the antenna so, you don't receive well.

Anyhow, I think we are all in agreement.  I don't know if I'd go down to 20
dBi, but perhaps 21 as Ed stated.  But maybe you are correct.  The dipole
feed is not efficient, etc......



Jon Ogden
NA9D (ex: KE9NA)

Citizen of the People's Democratic Republik of Illinois

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

http://www.qsl.net/na9d   <- Updated on 1/22/03!!!

"A life lived in fear is a life half lived."

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