Actually this setup is covered in this month's QST "The Doctor Is In" column
with a couple of references to older QST articles.
A center fed dipole with open wire or ladder line is a very good multi band
antenna if you have a tuner which will feed it. A half wave at the lowest
frequency is the classic antenna and is covered in the Handbook and Antenna
Book. Some people find that the high impedance of the full wave (e.g. 130' on
40m) is difficult for some tuners to handle and a 100' length is a popular size
for 80m and up. Myself, I prefer not to give up that extra length on 80m.
Antennas like this do not have to be precisely tuned. 135', 130', 125' all
will give essentially the same performance. 100' will give a slightly reduced
performance on 80m.
And additional plus of an antenna like this is that it will work very well on
the WARC bands like 60 and 30m.
I'm currently using an antenna like this. 40' of feedline to a 4:1 balun
outside the house, then coax directly to the Elecraft K3. The K3's internal
tuner handles it perfectly on all the bands 80 through 6m.
On Jan 15, 2012, at 7:31 PM, Jim Miller Waco Texas WB5OXQ wrote:
> I must move my 40 and 75 dipoles due to rfi in the house that I cannot
> resolve. I am thinking about 1 dipole fed with ladder line or window line.
> I have 2 possable support points.
> 1 pair is 126' from end to end and 50' high at one end and 30' at the other.
> Second pair 139' apart but 25' at one end and 30' at the other. The longer
> but lower is farther from the house by about 10' and runs over level yard
> with no obstructions. What is up with the 130' dipole fed with balanced
> line? Is this better for a multiband antenna than using 1/2 wave at the
> lowest desired freq? I have a MT-3000A Dentron tuner which is supposed to
> work with ballanced line. The maximum power I run is 800 watts rms not pep.
> Suggestions please. I have never used a dipole fed with balanced line. Will
> the window line take 800 watts or should I get the open wire feeder? I
> really only need this antenna to work on 75 and 40. I use my triband beam
> for 20+. How do you bring this line into the shack? Obviously it cannot
> touch anything metal along its run. Is the length of the feeder critical?
> Should the wire be long as possable or 1/2 wave at the lowest desired
> frequency? (3.9mhz)
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