[TowerTalk] simple gamma match

[jacobsen_5 at msn.com]

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 insulating.
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!!!!

73
K9WN  Jake