Topband: Re: ~ 1/4 wave 160 doublet
jimr.reid at verizon.net
Tue Oct 21 13:35:08 EDT 2003
Hi again from Kauai,
Thank you for the many notes from both Ten Tec and
Topband reflector users. Both groups offer some excellent
technical advice from great folks!!
A summary of notes and my responses:
1. Several said to put both wires of the ladder line together
at the tuner... and feed the thing right there..... making it into a
single T topped vertical .... with some ground radials or
a counterpoise along underneath. Use the single ended
output of the Palstar AT4K tuner, not the balanced output
terminals. This tuner I bought several years ago, and seems is
no longer sold.
My response: this means only the ladder line feeder is now
going to do the radiating. It is a 100 foot length of 600 ohm
(4 inch spaced) line. Or, about 0.19 wave length of a
frequency of about 1830 kHz. Unfortunately, the line runs
just four to five feet off the ground and along side two
bedrooms of our home for about 35 feet or so (with several
feet of excess line length folded around in the run) then rises
on up to the feed point of the doublet about 55 or so feet
high. So there is not much vertical portion to do much
effective radiating, with a lot probably coupling into the house,
and trees and bushes through which the line passes beside
2. Try hanging wire off the ends of your dipole to make it
1/3 wave on 160 I operate a 1/3 wave on 80 and it works fine.
That is certainly possible. This approach would require
adding some 27 feet of wire length at each end of the
present doublet. Unfortunately, I have no way to get the
wire any higher at the ends, so the added wire would
just be wandering about tied off to some scrub bushes
or low trees.
I suppose what I will have in the end is near vertical
radiation on 160, hi.
3. Add enough wire between the present ends,
some 270 feet long altogether, to make a half wave loop.
This could also be done, but the loop would be a long
horizontal rectangle, no where near square. The added
wire to close the loop could not be as high as the
present inverted-V 80 meter doublet.
4. And this thought: If your feed line plus half the antenna is
a quarter wavelength together you have low impedance
reflected to the tuner. And nearly resistive. Easy to tune. If your
feed line plus half the antenna is a half wave you have a high
impedance at the tuner, easy to tune with some tuners, again
Well lets see, at 1830 kHz feed ladder line is 100 feet,
or about 0.19 waves, and half of the 80 meter doublet is
about 62.5 feet, total 162.5 feet, or 0.3 wave length
total of feed plus half the doublet.
So neither of the above length conditions now, however,
I could shorten the 100 feet of feed ladder to get down to
a quarter wave over all on 160, some 134 feet for 1/4 wave.
Just outside having a look, and certainly there is excess
ladder line length, seems a total feed plus 1/2 the doublet
length to total the quarter wave length of 134 feet or so
I like this idea as the first approach now; most easily
accomplished at this time. All that seems needed to try
this is to cut about 28 feet of length from the ladder line,
brining it down to a 72 foot run.
5. Other ideas suggested:
5.1 Set up an inverted L...
As my antenna height is very limited, not sure the inverted
L or feed ladder acting as a short vertical radiator is going
to do me any good over the resulting short length, near
vertical incidence antenna that I can manage.
5.2 Put up a full sized 160 dipole, and make bends at
various points to get it to fit the lot. This zig zag method
isn't as good as putting up a 160 antenna in a
straight line. But it does work fairly well.
Another possibility for sure and would not require ground
radials or counterpoise as the vertical feed radiator or
Last time I was on 160 out here, I mostly heard, but
didn't work, a lot of fishing drift net beacons, hi. They
must be all around these waters together with the long
line fishers. Probably with a "cloud warmer" low wire
on 160 again, I might not hear much more again, but
at least I could participate in 160 meter activity around
the islands out here, what there is of it.
I will try Dr. Jerry's approach of the over all quarter wave
length of ladder line plus half the doublet length and see
what happens. If I understand his comments about the
line length plus half the doublet, and a low Z at the tuner,
I could safely use 1500 watts out, and perhaps be heard
be folks outside Hawaii.....maybe. Wonder if I could hear
them back, hi.
Thanks again to all and 73, Jim KH7M
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