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Re: [TowerTalk] simple gamma match

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Subject: Re: [TowerTalk] simple gamma match
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Date: Sat, 20 May 2006 14:46:09 -0500
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Dino is still having fun with his gamma match.

Dino,  I dug a 1970 edition of the ARRL Antenna Handbook out of the rack. Page 
264/265 gives dimensions for gamma's for 10/15/20 meters. For 15 it gives:
larger gamma tube is 3/4' x 6". smaller is 1/2" x 36". Uses polystyrene for 
spacing to driven is 5". Max inner tube insertion is 5". Max shorting bar 
length is 36".

Also found an old driven element for what I believe is an old 15 meter 3 ele. 
in my aluminum supply pile.  Outer gamma appears to be 3/4" x 10.25"  Inner 
appears to be 3/8" x 36".  shorting bar is placed at 24". spacing from driven 
is 5". Insulating material unknown (plastic of some kind) I don't know how far 
it is inserted into the outer tube.

Per page 265 of handbook: (paraphrased, sorta) with inner rod all the way in, 
and shorting strap at a "guessed" length, take a reading with your bridge at 
frequency wanted. Then adjust shorting strap for lowest swr at your chosen 
freq.  Tighten onto driven ele and then start pulling the inner gamma rod out a 
little at a time, tighten strap and take a reading.  Keep going until lowest 
swr is reached. Then readjust shorting strap to lower swr more. You may have to 
go back an forth several times. REMEMBER, readings are taken at your CHOSEN 
operating freq.

Of course this all assumes that the overall element lengths are correct to 
begin with.

Once again, good luck with your project, and remember, YMMV, and There ain't no 
such thing as a FREE lunch. But then, that's what makes antennas so much fun. 
Makes ya think about what your doing. Other wise ya go CRAZY!!!!

K9WN  Jake

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