Stacking antennas (How much is too much?)

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eHam.net Forum : Elmers : Stacking antennas (How much is too much?)

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Stacking antennas (How much is too much?)	Reply
by KB3KTY on June 7, 2004	Mail this to a friend!
Hello again, I am putting up a ~48' Rohn self-supporting tower and mast(w/HAM IV rotator) to support a Cushcraft A3S (with 40m add-on kit) and a Cushcraft 6m(horizontally polarized)/2m/.7m beam, 4 1/2 to 5 feet above it (as per the Cushcraft support tech's instruction). Now I'm thinking about moving my Butternut HF9V vertical to the top of the stack, which is currently attached to a wooden fence post and raised up about 7' off the ground. According to the HF9V manual, I would just need to have 4 radials at 45-degrees to the tower. I might attach these as extra guy wires to the top of the tower unless there's a better idea... The wind load figures work out for all of this, plus I figure that the added guy wires give me a little insurance. IS THIS PLAN NUTS OR AN OK IDEA? It gives me a raised vertical 6m antenna for FM, plus much better height for the Butternut overall. It also gives me a nice central location for the remote antenna switch and shorter coax runs. I don't know how the antennas might interact. I can get a longer mast if more separation is needed. Thanks and 73 to all, Mike KB3KTY PS Bonus question: What's a good homebrew method of staking the "guy wires" to the ground? - remember this is a self-supporting tower so overkill is not needed..

RE: Stacking antennas (How much is too much?)	Reply
by K5LXP on June 7, 2004	Mail this to a friend!
It's plain nuts. The radials need to be connected to the base of the vertical at the feedpoint, not 5 feet below it. Performance wise (except maybe 6M) the butternut's not going to work any better up there than it would on the ground with a better radial system, so save the tower for antennas that would benefit from it. A 2M/440 dual band base antenna would be very useful up top and adds very little wind load to the tower and rotor. Mark K5LXP Albuquerque, NM

RE: Stacking antennas (How much is too much?)	Reply
by AA4PB on June 7, 2004	Mail this to a friend!
I would think that you are going to have some interaction between the HF vertical and the HF beam which is just a few feet below it. Granted you get some "decoupling" benefit from one being horizontal and the other being vertical. Personally I'd find somewhere else for the HF vertical.

RE: Stacking antennas (How much is too much?)	Reply
by WB2WIK on June 7, 2004	Mail this to a friend!
I agree with Mark. The Butternuts (HF6V/HF9V etc) perform better when they're lower with lots of radials, and placing a structure this tall at the top of a mast over the tower is an accident waiting to happen -- not to mention the fact that it puts the vertical so far out of reach, that if you had to make adjustments to it (as all Butternuts require adjustments every time they're moved to a new position), you wouldn't be able to. The "four radials" for an elevated vertical such as the Butternut does not imply four radials TOTAL, but rather four radials PER BAND. If you have an HF9V, that would be 36 radials total, four each for nine bands. There is no radial length that will serve multiple bands properly for an elevated installation. And as Mark said, the radials must be attached directly to the antenna bracket, not inches or feet below it, so using radials as "guy wires" isn't going to work. You didn't mention which tower model you have, but if it's 48 feet and self-supporting, it may be a "BX" series like HBX48 or HDBX48: In which case, those towers are self-supporting only when using antennas having element or boom lengths shorter than ten feet. A 25G or 45G is not self-supporting at 48 feet; so I'm not sure what you have there.... WB2WIK/6

RE: Stacking antennas (How much is too much?)	Reply
by N6AJR on June 7, 2004	Mail this to a friend!
go to Sporty's on line, they have screw in anchors with 6 foot long tie down bars on the for tying down aircreaft and they work good as anchors for Ham stuff. you use a long bar to screw them into the ground

RE: Stacking antennas (How much is too much?)	Reply
by KB3KTY on June 8, 2004	Mail this to a friend!
Follow-up: Thanks all. I will not attempt to put the vertical on top of the stack! 73s, Mike KB3KTY

Another idea ...	Reply
by KT8K on June 8, 2004	Mail this to a friend!
I have an HF9v, and getting that thing vertical and holding it there in order to slip it over a mast is a MAJOR effort for me (and I'm 6'2" 225 lbs and work out frequently). Doesn't sound like a safe thing to be doing at the top of a tower. Can you feed (gamma match?) the tower itself? That would be a bigger vertical ... I know a gamma match is not broad-banded, but have known friends to use motorized capacitors and sometimes relay switched inductors to tune towers before. Curious ... I've yet to put up a tower for myself. Good luck, be safe!, and 73 de kt8k - Tim

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