Hi Rick-
In regards to copperweld near the ocean, here in California wire near
the coast, my copperweld has not held up too well as the steel rusts
then fails due to intrusion through any damage to the copper surface.
solid copper will last much better.
BTW I understand the utilities use solid copper wire instead of
copperweld or aluminum for same corrosion reasons. Someone else may be
able to verify this info.
I'd feed the dipoles with open wire and use a good matching unit..
possibly a remote unit and real open wire feed is also less noticeable.
( old Johnson Matchbox works for me everywhere except 160, I'm building
one for 160. the 2 small holes coming into the shack easy to insulate
and easy to fix later....it does take some ingenuity to route though)
another possibility is a loop corner fed w/open wire, open at opposing
corner for 160. makes a low visibility antenna, try modeling and see, my
235m square loop at 10m high does ok for a stealth antenna on
75/80/30/40. sometimes all you can do is try some things and see what
works for u at a particular location.
73, Renée K6FSB
Rick Kiessig wrote:
Until recently, I was planning to put up an inverted-L as a TX antenna for
80 and 160. However, things have changed, and it no longer looks like I'll
be able to run the radials I would need to have an effective vertical. Now
I'm leaning toward a low dipole.
My site is highly constrained: it's near the top of a ridge, on a slope,
facing the ocean (100m above sea level, 300m from the water). The highest
spot above sea level is the top of my tower: it's only 8.5m above immediate
ground level (next to the house), although the ground 10m away is 7m lower.
I can't run more than a wire or two and a coax feed on (not above) the
ground - an FCP, for example, would be much too large. Due to limitations
imposed by the city, I can't go higher than 10.5m above ground level.
If I run a wire around three sides of my property in a U shape, hung from
the tower near (but not at) the feedpoint, I can just hit 80m total length,
with a 46m long center section and two 17m long end sections. The wire would
attach to 10m high fiberglass poles near each of the four corners of the
property.
I recently built a dipole for 40/20/15 using 300 ohm twinlead, which worked
out very well, so I'm thinking of using a similar approach for this antenna,
using the full length for 160, and trimming one wire to be resonant on 80.
I'd like to do whatever I can to maximize bandwidth. If I could cover both
80 and 75, for example, that would be great.
Questions:
-- Is a low dipole for 80 and 160 on a sloping site like mine worth the
effort? I'm interested in DX, not NVIS.
-- Given my constraints, are there other types of TX antennas I should
consider?
-- What's the best wire to use to minimize stretching and to maximize
bandwidth and efficiency, and that can handle full legal power? I will need
at least two (maybe three?) wires to cover both bands. Copperweld is strong,
but I've heard it can be lossy, too. Twinlead has two wires, but it's
stranded and doesn't feel very strong.
-- I'm thinking about using Spiderbeam black fiberglass telescopic poles at
the corners. However, I'm concerned about durability in high winds and
having enough strength to be able to tension the wires so they don't droop
terribly. Is there a better choice?
-- I'm planning to put a common mode choke at the feedpoint and run coax
from there, as I've done with the other dipole. Any reason to do it
differently?
73, Rick ZL2HAM
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Topband reflector - topband@contesting.com
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Topband reflector - topband@contesting.com
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