Wow, do I appreciate the quantity and quality of the responses to my
first post to TowerTalk; I assure you all this is not a philosophical
query, but a serious plan to build this antenna.
I had hoped to test this antenna for the CQ WW SSB, but it turns out
that Irish Solicitors are as slow as American Lawyers in drawing up
contracts for our new vacation/contest QTH in County Clare, so it
looks like the CW test in November might be the first chance.
As KG4CS in Guantanamo 1970-1972, I was able to put a 1,400 foot long wire
using single conductor #12 insulated copper wire that ran South to North.
Fed from the South, supported by a 35 foot power pole on a 100 foot bluff
on Bargo Point, over a salt water inlet, the North end was at 175 foot on
a wooden pole at the AFRS station. Using my 13 foot boat with 6 hp Sears
motor, I reeled the wire across the bay, into which it of course sank; I
boated to the dock at the south end, drove the car to the north end,
hauled up all the slack I could, drove back to the boat, ran it along
the wire to lift it out of the water, back to car, haul out the slack,
etc., for five or six times until the wire was finally out of the water.
But with max downhaul pull of roughly 200 pounds tension, I could only
get the bottom of the catenary up to about 30 feet, for a big sag of
105 feet from the low end. That wire survived several heavy storms
while I was there. And it was there long after I left Gitmo.
Especially on 160 meters, that antenna was stunning; it outperformed a
full size 160 windom at 60 feet, and on 80 and 40 it was significantly
better than the windom, dipoles, and a HighGain Vertical with base at
20 feet on top of our concrete reinsforced quarters with halfwave radials.
I am sorry now I never tested it on 20-10, where I had a 2 el quad.
With 75 watts out of a modified ART-13, and double conversion reception
with a Navy RBD tank receiver as first stage (great RF, no filters, but
it had a 910 KHz IF) into a second stage SX-43 (poor front end, but
great crystal filters) and especially due to that long wire, in 1971
I brought the CQ WW CW 160 record to North America for the first time,
with 36 countries and 11 zones (and, remember, this was when EVERYONE
on top band was really LOW POWER). So I'm a long long wire believer,
and now I've got a new opportunity to experiment!
Several replies suggested the sag problem might be resolved with additional
tension to bring the sag to less than 50 feet for the 1200 foot SPAN,
(thanks to a 2000 posting from K6LL, I learned SPAN was half the distance!).
Some very astute and practical solutions to control tension were suggested
that will likely be implemented.
But my original sag problem was based on the recommended maximum of the
tension being no more than 15% of Breaking Strength of the wire; all of my
calculations, for all of the copper and copperclad wires in the ARRL Handbook,
and for all of the suggested alternatives, ended up with tension values
between 30% and 50% of that wire's Breaking Capacity, or 2-3 times the
recommended tension.
But then, researching what the heck Aeolian Vibrations were, I stumbled
onto the decription of a commercial power cable in France with a two
kilometer span; it's design point is for constant tension of 57% of the
breaking strengh of the special cable designed for this purpose!
If 57% is safe there, my 30-40% now looks feasible.
But there are other limits I didn't specify: the far end of the long
wire can only be connected to an eyebolt on an existing thin 4-foot
fence pole; there can't be any additional hardware at that end,
which limits the maximum tension which then limits wire size.
However, there is also the visibility issue since we are on the
scenic west coast, and the inlet is viewable from a road that
crosses the river that feeds the inlet, so smaller wire is
preferred to minimize tension. I also will need to share a few
pints of Guiness with the few nearby neighbors who might be able
to see the wire, and, especially, with guy who owns that fence
post I plan to use. I also plan to run only 100 watts to
eliminate any RFI issues. (Well, at least for the first few years!).
So, my initial plan now is to use 17 gauge aluminum fence wire,
which weighs under 3 pounds per 1000 feet, and has a 90 pound
breaking strength. I calculate that a 50 foot sag will have about
40 pounds tension, or 40% of the breaking strength. It's also
cheap, and available at farm supply stores.
I fully recognize that wind loading may be the additional force
that breaks the wire, but at least now I feel it's worth
the effort to try.
And if it does stay up, K6LL can test his vertical vs longwire
hypothesis; I do plan to also install a serious vertical. And
the long wire aims 320 degrees, which looks pretty dead on for
California (Dallas is at 290).
(Dream: Long Wire Front to Back, plus below-the-bluff sag
shielding blocks the East so well that I can only hear the
USA on the wire, and need a Vertical for Europeans.)
Now, for my final question: assuming the 800 meter long wire does
stay up, would it do any good to use it for the right leg of a
V-beam? I can run the left leg also for 800 meters, along the
fence posts at the edge of the bluff, which is at 240 degrees.
That would be a vee angle of 80 degrees with centerline at 280
degrees, but the vee beam charts I've reviewed suggest that
that's way too large of an angle for those leg lengths.
Any experience here?
73
Barry, W5GN
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