[Top] [All Lists]

Re: [Antennaware] re vertical with metal roof as groundplane.

To: "George Warnock" <>, <>
Subject: Re: [Antennaware] re vertical with metal roof as groundplane.
From: "Guy Olinger, K2AV" <>
Date: Sun, 1 Mar 2009 17:02:30 -0500
List-post: <">>
----- Original Message ----- 
From: "George Warnock" <>

>>the radials will be following the pitch of the roof... is this a 

The task of the radials in your design is to behave as a non-radiating 
non-lossy current sink, a place to store the opposite charge carried on the 
feedline shield. The radials are opposing in order to cancel out induction 
and radiation on their part to the largest degree reasonable.

Laying a tuned radial (what you are doing) on or close to the roof will 
force undesired current IN the roof, less as you separate.  While not a 
killer, that is not part of the task of the radial. Simple physical reality 
forces some degree of closeness. You separate radial and roof until it 
becomes difficult or mechanically unsimple. Judgement call by the one on the 

A 40/80 vertical is certainly feasible, though the dimensions you give 
suggest 40m.  I thought you had specified a multiband antenna previously, 
which was one of the assumptions in my postings.  On 80m, the end of  two 66 
foot radials can be bent and pulled away parallel to the ground, forming a 
half-swastika as seen from over head.  I have seen coax center conductor 
laid along a wooden fence top rail to complete a radial in this fashion.

Feasibility on 80 is mainly construction feasibility, practical height, 
weight, guying, etc, etc.  A simple quarter wave wire on the low end of 80 
is 66 feet.  If you can buy, borrow or build the multiband radiator and get 
it survivably in place, the location particulars you have described are not 
a detriment, if anything an improvement over what is usually available and 
done at the ground on 80m verticals.

If you were talking about only a 40m vertical, then there is no reason not 
to use a 4 quarter wave radials over the roof and get the likely 35 ohms up 
to 50 using a coax-based series matching transformer which will work very 

73, Guy.

Antennaware mailing list

<Prev in Thread] Current Thread [Next in Thread>