[TowerTalk] Best wire antenna for 75m/80m DX coverage

[Pete Smith]

At 11:15 AM 10/20/98 +0000, Barry Kutner wrote:
>
>I use 3 "vertical slopers" around the tower. I believe it was 
>originally written up by K8UR, and is in the ARRL Antenna Handbook 
>(mine's about 10 years old, don't know if it's still there) as a 40m 
>antenna, using 5 slopers.
>Start at the top of the tower with one end, then the lower end is 
>pulled back in to the tower, so the center insulator is half way up, 
>and pulled out by a rope and staked to the ground.  It looks like a 
>diamond configuration.  Pulling the lower end back in cancels out the 
>horiz component and lowers the andle of radiation.  The wire is fed 
>with a 3/8 wave of coax (I used RG8X) to a relay switch box.  This 
>length of coax is supposed to act like a stub, making the non-selcted 
>wires act like reflectors.
>To switch from 80 to 75, I go outside and fold back about 10 ft at the 
>bottom.  In the near future, I plan on adding some relays to do this 
>from in the shack, and if anyone has any suggestions on physical 
>construction details (what to use to keep water out, how to support 
>it, will the control wires bring RF into the shack, etc.), I'd apprec. 
>it.
>I'm very pleased with performance, and at times see up to 20 db, F/B or 
>F/S depending on the path.

This is a great antenna -- depending on who you talk to, credit goes to
W9LT, K3LR or K8UR.  Whatever....

Just a couple of comments -- according to modeling and my practical
experience, it works much better above the resonant frequency of the
elements than below, quite independent of the length of the coax feedlines.
 F/B goes away quite quickly below resonance, and actually peaks a couple
of hundred kHz above.  I cut mine for the very bottom of the CW band, and
run it on 75 without change (good ol' SB-220 will still match it up there).

Also, the shield of the feedlines must also be floated -- I used a
weatherproof plastic electrical junction box for the relays, so that I
could use SO-239s.  I think the K8UR design used terminal strips to
accomplish the same thing.

The very best way to do this is to make the upper half of the dipoles part
of your guywires.  If you do it separately with normal materials (wire,
nylon cord, etc.), you'll probably discover, as I did, that there's a big
tradeoff between tension on the antenna wire and the space required around
the base of the tower.  I wound up using almost a 250-foot circle for my
4-dipole version.  


73,  Pete Smith N4ZR
In wild, wonderful, only middlin' rare WEST Virginia



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