|[AMRadio] AMRadio Digest, Vol 132, Issue 11|
aar7ir at hotmail.com
Fri Jan 16 15:53:45 EST 2015
This is great, thanks so much for taking the time to share ! I'll
keep you up to date with my progress.
From: AMRadio [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Donald
Sent: Friday, January 16, 2015 3:36 PM
To: amradio at mailman.qth.net
Subject: Re: [AMRadio] AMRadio Digest, Vol 132, Issue 11
To answer your question, I tried to respond by e-mail, but my message
bounced. Others here considering using open wire line might be interested in
the same thing, so here it is.
Look in your 1965 edition of the ARRL Radio Amateur's Handbook, or an
earlier one if you have one around. I'm less sure about the big thick
recent editions in the large format; they took a lot of the practical stuff
out, making them all but useless as a source of basic homebrewing
information, at least for the kind of stuff I like to build. The last new
one I bought was about 10 years ago and I thought it was a waste of money.
My OWL consists of #8 copperweld spaced 2 1/2 inches apart, and #10 spaced
2" apart. Some of the spreaders are homemade while others are the little
EF Johnson 2" ceramic jobs. The impedance calculates to 438 ohms. I used
that impedance because of the availability of the 2" spreaders; I had a
bunch of them on hand. The 2" spacing is also ideal for feeding up through
the interior of the tower, at the geometric centre of the triangle, rather
than the usual Hammy Hambone technique of a Rube-Goldberg outrigger to space
the line some distance away from the tower. The heavier line, the 140'
long run from shack to tower, uses wider spacing to maintain the same Zo
with the larger diameter wire, in case I ever have a reason to connect the
entire thing together to form one single tuned feed line.
I used copperweld wire simply because I had it available; I had acquired
several thousand feet of #8 and #10 over the years. If I had to buy new
wire, I would have looked for solid #8 hard-drawn copper for the
shack-to-tower OWL. Copperweld is too stiff for easily making OWL, but good
for antenna wire since it is practically indestructible. The older chap (now
SK) who gave me the roll of #8 had used the stuff as guy wire for a couple
of 100' towers, and they had been up for over 10 years.
The spreaders are attached to the line using short pieces of smaller gauge
copper wire, just as described in the older handbooks. The main transmission
line wires ride in the grooves at the ends of the spreaders, with the
smaller wire threaded through the holes near the ends of the spreaders and
wrapped round the main wires to hold them in place. The run up the tower,
OTOH, is held in place by spacers made out of plexiglass sheet, one every
10', fixed to a set of rungs on each tower section. Each spacer has two
holes drilled in it, 2" apart, with the wires threaded through the holes as
they run down the tower. Tension on both the OWLs is maintained using small
turnbuckles. I used a come-along for the initial tension on the shack-tower
line while I was putting it together.
The shack-to-tower line is matched (flat, non-resonant, with no standing
waves), while the line from enclosure at the base of the tower up to the
doublet operates as a tuned line with standing waves. Since I designed and
built the transmitter and antenna feed system myself, it was my decision to
designate the tuned circuits at the base of the tower as an integral part
of the transmitter; this final stage of the output network is linked back
to the earlier stages via the untuned line, while the tuned feed line
running up the tower is designated as the antenna transmission line. That
configuration tunes more satisfactorily than would one long tuned feed line
with an "antenna tuner" in the shack. The network stage at the base of the
tower is remotely tuned from the shack, using a reversible DC motor, ganged
with a meter rheostat on the same shaft, to indicate the setting of the
If you have any further questions, please don't hesitate to ask.
I'm back near DC again having abandoned my plans of moving back to
the Midwest. So now I need to restring all my antennas and I want to do it
right this time.
You mentioned not using the commercial (and assumed crappy) open
line. Can you tell me of a good place where I might read about the proper
construction and measurements to this open line you homebrewed. I need to
start at the beginning and study the entire matter.
Any assistance you can provide would be greatly appreciated.
I hope to be back on the air again soon with my Valiant and my 1965
ARRL handbook homebrew superhet !
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