[TowerTalk] Feeding a Delta Loop

[Kenneth R. Goodwin, Jr.]

I went for horizontal polarization with the feed point at the apex at 
the top of the 80 foot tower.  I used a quarter-wavelength RG-11 line 
as an impedance match for the 100 ohm antenna feed impedance to 52 
ohm RG-8 coax to the station.  My baseline reference is the W1FB and 
W1SE article in the October 1984 issue of QST (page 24) which details 
all possible configurations.  When I lost a few of my pine trees that 
support the base leg to pine bark beetles this past summer, I had to 
move the end supports. I was surprised as to the sensitivity of the 
SWR to lengths of the three legs.  Not having all three legs 
reasonably equal caused a significant difference in the SWR.  Guess I 
was lucky the first time I put it up 20 years ago so on the new 
configuration I constrained the insulator connections to the base leg 
with wire rope clips.  Over the years, I've ended up preferring 
insulated wire over bare copper wire - just lasts much longer in the 
high humidity environment.  For K5KKV's benefit, the overall length 
of the delta loop is 1005 divided by f in MHz which makes it a full 
wavelength.  For 80 meters that would three legs around 95 feet each 
or a total of 285 feet/86 meters.  Ken K5RG