[TowerTalk] Shunt Feeding Towers

[dan hearn]

Info on shunt feeding towers is in the ARRL Antenna Anthology, p35. The
anthology consists of reprints of articles from QST. Mention is made of
the author being Earl W. Cunningham, K6SE but no date is given for the
QST issue. There is also mention of an article in Ham Radio for May,
1975. I have seen that article and I believe it has charts for different
tower heights.
  The AA article describes 5 different shunt fed tower installations.
The towers range from 50-86 ft. and most have Th6DXX yagis at the top.
The following are - Tower height,wire tap point in feet,wire spacing in
inches, and gamma capacitor value.

69,68,30,150pf---86,75,24,125pf---64,63,8,300pf---70,68,24,225pf---

50,47,44,400pf. These values are for 160m.

 There is a sketch for the first described system above which belongs to
W5RTQ. He also has a second feed wire tapped at 28 ft. and spaced 15
inches from the tower. He uses nr. 8 wire for both feeds. This 80m feed
uses an Omega match with a pair of 150pf variables. My friend K5AQ uses
a 2 band system like this on 80/160 on a crank up tower and has worked,
I believe , over 200 countries from his Texas location. 
  I have used the Omega match to feed several towers. In one case the
tower was an 85 ft windmill type with a 4 el 20m yagi on top. The first
tap point I tried was at about 50 ft and the spacing was 24 inches. I
had 16 radials 1/4 wave long buried 4 inches. A good match was obtained
and the bandwidth was 55khz for 1.5 SWR. 

73, Dan, N5AR

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