Topband: Low band antenna project questions
nc3z at outlook.com
Mon Mar 7 15:37:22 EST 2016
OK, this has me intrigued. So the T top would look like this if looking
straight up (or straight down) with the vertical portion at the xx?
My 160M dipole is actually a 160/80M fan and resonates well on both
bands, I did not think I could do that with a T top. That would solve
Would a cage of vertical wires be better than if I could use 2.5 to 1.5"
Luckily in our rural local club we have 2 hams that sell some neat
products, one is the Air-boss launcher and the other is the Antenna
Tensioner. The tensioner has proven its self here in the eastern NC
winds. And being a boating area I have several West Marine stores nearby.
NC3Z/4 Pamlico County, NC FM15
On 07-Mar-16 12:48, Jim Brown wrote:
> Hi Gary,
> The antenna you describe should work quite well on both bands, but I'll
> suggest a couple of tweaks to make the matching easier. First, make it a
> Tee -- if you have a catenary, you can support a Tee as easily as an L.
> Second, make the top section a fan (like a fan dipole) with short
> elements to resonate it on 80 and longer ones for 160. Third, don't
> worry about remoting the tuner unless you feedline is very long. Unless
> the match is really bad, feedline loss on 80 and 160 is pretty low,
> especially if you use RG8. Also, you can make the tuning more broadband
> (and electrically lengthen the vertical section by 1-2 percent) by using
> two parallel runs spaced 12-18 inches, tied together top and bottom. Do
> a simple NEC model to get dimensions.
> Finally, use as many radials as you can, don't worry a lot about length,
> just think more is better. :) BTW -- 50 ft on the ground will be close
> to a quarter wave on 80, 100 ft on 160.
> As to physical details -- get a good pulley at each end, tie one end
> down, put a weight on the other end, and use some sort of "mechanical
> fuse" at the feedpoint so that wind doesn't break it. I use a mating
> pair of Pomona connectors -- when the wind blows, they simply un-mate.
> For the fan spreaders, cut short lengths (12-18 inches is great) of
> 1/2-in PVC conduit, drill holes about 3/4-in from each end to pass the
> wires through. Make this antenna as physically robust as possible to
> withstand the wind. At a minimum, #10 THHN for the long top sections
> that carry the stress. #12 or #14 is fine for the shorter top sections.
> Don't make any soldered connections -- they don't weather well, and wire
> tends to break at a soldered joint. Instead, use split-bolt copper clamp
> connectors sized to fit the wire you're using. For support rope, use
> 5/16-in rope from http://www.synthetictextilesinc.com/supportham.html
> It's resold by lots of ham vendors, but Synthetic Textiles is a bit
> cheaper. Smaller rope is sufficient for strength, but you'll appreciate
> the larger size when you're trying to pull on it to maximize tension,
> which pulls it higher. :) Don't use hardware store pulleys -- instead,
> use marine pulleys (good) or this excellent "rescue" pulley, which is
> also easy to rig.
> Out here in CA, the West Marine is the place to buy marine pulleys.
> 73, Jim K9YC
> On Mon,3/7/2016 5:50 AM, NC3Z Gary wrote:
>> Now I want to be able to use this antenna for 80M as well as the non-DX
>> portion of 160M. I can house a autotuner at the base (or make my own
>> network but that would require control lines). My thinking is to make
>> the 160M a 5/16 WL vs 1/4 to be more beneficial to 80M tuning without
>> loosing anything on 160M.
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