Topband: Low band antenna project questions

[Jim Brown]

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.

http://www.ropescoursewarehouse.com/catalog1/advancedwebpage.aspx?cg=1851&cd=4&SKUTYPE=202&SKUFLD=SKU&DM=1250&WEBID=914&gclid=CKfCobGOr8sCFQWUfgod5DUOHQ

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.