>What about 450 ohm ladderline? What is the math for it?
>...so I am looking for a short antenna, ...cut for 30m or 40m,
Hi Matt, the BASIC program I posted is ideal for doing what you want to
do. 3/8 wavelength is about the shortest efficient antenna so that would
make your dipole 50 ft long. EZNEC sez if you feed it with 71 ft of 450
ohm ladder-line, the result through a 1:1 current balun/choke will be
a resistive 20 ohms on 7.1 MHz with an 50 ohm SWR of 2.5:1. Adding 8.5
ft of 450 ohm ladder-line gives a resistive 91 ohms which is a 50 ohm
SWR of 1.82:1. Although these are not bad SWRs, I would take along an
antenna tuner.
As always, EZNEC results are only approximations and are a starting
point before trimming to perfection.
73, Cecil, W6RCA, OOTC
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