Lee:
Re: 40 meter dipoles 50' up
Your problem is essentially the same one brought up recently by Dave
Leeson. The feedpoint impedance of a dipole for 40 meters at that height
is somewhere in the 70-90 ohm region at resonance. Hence, a narrow 2:1
SWR bandwidth.
Solution #1: place a 1/4 wl section of 75-ohm cable from the antenna
feedpoint to the junction with the 50-ohm cable.
Solution #2: if the bandwidth still does not cover 40 meters completely,
place a 1/2 wl length of 50-ohm cable from the antenna to a point in mid
air. Then add the 1.4 wl 75-ohm cable section. Then continue the 50-ohm
cable run to the shack. This second system broadens the operating
bandwidth even further.
The latter system is Dave's idea based on ideas from Frank Witt and
others.
Hope this is useful.
-73-
LB, W4RNL
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