low band thoughts

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low band thoughts

Post  W5GA on Sat Aug 03, 2013 12:21 am

Been doing a little thinking on how to best improve things on 80/160 here. One of the ideas I've run across is to use the tower as the vertical leg of a combined 80 vertical/160 inverted L, with a trap at the top to isolate the 160 wire. I'm sure I'll need some sort of matching network at the base, because the tower/mast combination is too long on 80. The tower is 72', and the mast goes another 15' above that.

One of the concerns is that the L part of the deal for 160 would necessarily come off the top of the tower, which is some 15 feet below the top of the mast. Unless I'm terribly mistaken, the mast would be part of the vertical radiator. Does anyone have a clue how that 15' sticking up above the horizontal component will affect things?

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Re: low band thoughts

Post  N8YX on Sun Aug 04, 2013 11:58 am

W5GA wrote:One of the concerns is that the L part of the deal for 160 would necessarily come off the top of the tower, which is some 15 feet below the top of the mast. Unless I'm terribly mistaken, the mast would be part of the vertical radiator. Does anyone have a clue how that 15' sticking up above the horizontal component will affect things?
Try modeling this in EZNEC?

That 15ft mast section will look capacitive (think capacitance hat) to the balance of the radiator. Which is a good thing, as it will increase the bandwidth slightly. The horizontal radiator portion isn't high enough in the air for the stub to make much of a difference in pattern.

If you have supports around the mast itself (think tall trees) I would run two or three 40ft horizontal sections perpendicular to the tower as a capacitance hat then ground the tower and shunt-feed on 160 with a gamma match. A remote-controlled vacuum relay enclosed in a box inside the tower can be used to disconnect the horizontal sections when operation on 75/80 is desired, and a separate gamma section/feedline can be used for matching on 75/80.

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Re: low band thoughts

Post  N2RJ on Mon Aug 05, 2013 10:11 pm

One thing I've been considering is how K9RS did it. He put a four square using inverted Ls hung off catenaries on the tower.

He did it with an 86' tower but you can do it with a 72'.

Check it out from his 2008 Dayton presentation.

EDIT: Sorry I can't post links just yet.

Google K9RS 4 square.

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Re: low band thoughts

Post  W5GA on Thu Aug 08, 2013 9:32 am

Thanks guys!

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