[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Re: Antenna Selection

    Trees absorb *vertical* polarisation better than any other. So common sense
    sez: don't go for vertical polarisation. True circular pol would probably
    get distorted too; others will probably know more about this.

    I wouldn't say "go buy a horizontal beam" ... but it might be worth
    delaying your purchase for a while and borrowing one to see what happens.

I think the "borrow" idea is an excellent one.  It not only depends on 
your local situation, but also that of the birds you're trying to work.  
For example, to my experience (which KI0AG told me about first) AO-27 is
vertically polarized until MEL, then tends towards horizontal, at least 
until close to the horizon. (Some low elevation passes excepted, i think.)
At most activity occurs on the first half of the pass for most folks.
So horizontal polarization wouldn't be very useful for AO-27, except
maybe in the northern half of Canada.  (I wish that weren't the case, as
i could mount the antenna i use for portable operate on a cheap rotor at
a fixed elevation and not be involved in all the complication with patch
cords and cassette recordings necessitated by using a hand-held antenna.) 
So know your own needs and get a antenna that's good for *your* needs.  
And if you also want to use it for terrestrial work, that will changes 
things, too.

Sure, circular polarization might get distorted by trees.  But are you
looking for exact circular polarization, or are you merely looking for
polarization diversity??  Yeah, you might lose a few dB by being in the
trees, but that beats the hell out of fighting with neighbors or your
homeowner's association about antenna restrictions.  And if you have a
choice between fixed linear polarization and distorted circular, it is
my comparatively naive opinion that you'll probably be happier with the
latter unless the satellites you want to operate are always in the same
fixed linear polarization as the proposed antenna.  Or are all operating
in circular polarization.  Circular works with linear with a minor loss,
but the wrong linear polarization loses badly, as does having left/right
mismatch in circular polarization.  There is no "magic bullet", but some
things work alot more of the time than others.

			-- KD6PAG  (Networking Old-Timer, RF newbie)

Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org