w8ji at w8ji.com
Thu Jan 19 09:17:02 PST 2012
> I am planning an EDZ for 10mhz between two towers at 90 feet. My basic
> questions are:
> If I only want it for 1 band.....
> a. Can the ladder line be any length if the balanced tuner is directly
> beneath the antenna?
> b. Could I make a stub as per formula, use a 4:1 balun at the end of the
> stub, and run coax into the shack to a tuner near the transmitter?
Don't use a 4:1 balun. The impedance presented by the feedline to the balun
is not likely to be close to 200 ohms j0, and a 1:1 current balun always
does a better job with mismatched loads for the same cost in materials.
Also, if you trim the feeder to the correct length you can have nearly 50
ohms J0 without a tuner. All you need to is pick the sweet feedline length,
and you will be matched close enough to minimize losses on a coaxial feed.
Normally that length for the balanced line, electrically, is about .17
With two stubs of appropriate length, or an adjustment between balanced
feeder length and antenna length, it can be made 1:1 without any tuner at
My 80 meter EDZ antennas, 330 feet long, use a 47 foot long balanced line,
and come out about 50 J0 ohms. By proper choice of line length, line
impedance, and antenna length the antenna can be made to work 160 and 80
with a low SWR, with no switching, and a low SWR on both bands. It is an EDZ
on 80, and a long dipole for 160.
That won't do you much good on 10.1 MHz, because the half frequency is 5.05
MHz, but it might be nuzzled up to the 60 meter band and still work as a 30
meter EDZ with some playing.
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