w4au at verizon.net
Thu Jan 19 12:20:31 PST 2012
Tom has it right. I have a EDZ for 40 that is ~190' long, horizontal, and
is fed with 17' of 450 ladder line. I get very close to 50 Ohms, 0j at the
feed point where I have a 1:1 balun. No tuners are needed, but with a tuner
it does a credible job on 30M, 20M, and 17M, too.
73 - John, W4AU
At 12:17 1/19/2012, Tom W8JI wrote:
> > 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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