In a few days I'm expecting to mount a Cushcraft R7000 multi-band (HF) vertical antenna on top of a metal mast that will be attached to the outside wall of a large metal shed. The aim is to have the base of the antenna stick out above the roof of the shed and so have an unobstructed signal path in any direction.

This particular antenna doesn't need a system of ground radials but instead uses a matching network, part of which is provided by a set of seven 49" (124.5cm) long steel rods that stick out in the horizontal plane (like a bottom-placed capacity hat).

R7000 matching network

The documentation mentions to horizontally space the antenna sixty-six (66) feet from any surrounding metal, but I couldn't find any information on the amount of clearance above a steel sheet roof. I'm thinking of leaving a space of about 3 feet between the roof and the capacity rods but that figure is just pulled out of a hat.

At what distance above a metal roof will the capacity bottom-hat of the antenna's matching network not experience a significant disturbance in a) resonance, b) take-off angle and c) perhaps any other main factors I didn't mention here?

It would be nice to know if the antenna would be similarly resonant in the car-park where it could be easily tuned as well as on top of the shed.

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    $\begingroup$ The instructions say, "If you use volunteer helpers be sure that they are qualified to assist you. Make certain that everyone involved understands that you are the boss and that they must follow your instructions." Not really related to your question but I thought it was funny. $\endgroup$ – Phil Frost - W8II Jun 18 '14 at 3:13

The R7000 and 7000+ are NOT quarter wave verticals they are HALF wave verticals( check dimensions you'll see starting 10 meters that its not 8ft=quarter wave , its about 12-13 ft , shortened from 16ft because of the traps)., the spokes at the base are NOT radials they are Counterpoises, 3 feet distance is not enough above metal roof or even an AC unit(I tried my AC unit and could never get ALL bands right), I suggest at least 8 preferably 10 ft above a metal object which Cushcraft exactly suggests if ground mounting the antenna.If u are using a metal roof, thats ur ground right there so we follow manufacturer's guideline=8 to 10ft.

  • $\begingroup$ 4BTV IS NOT a similar antenna to the R7000, one is quarter wave the other is half wave.oranges and apples, you are confusing this owner. a half wave verical which the R7000 is, does not need radials or ground , it is a complete antenna however shortened, $\endgroup$ – Varoujan Kalinian May 27 '16 at 4:04

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