Bob
You do not give the dimensions of your roof. I will say, however, that my
experience with the metal roof was very good. I had a 40x50 metal shop in
Ellensburg that I mounted a pair of verticals on for a set of phased
verticals. The verticals I used were HyGain 14AVQs fed in accordance with
the HyGain Tech Note for Phased Verticals. The verticals were mounted 1/4
wave apart for 40 meters and fed in a manner to allow switching between in
phase and plus or minus 90 degree feeds thus, in theory, permitting
switching between broadside and plus or minus endfire cardioid patterns.
The systrem worked well even without bonding the metal panels although the
entire building was metal in my case. and a tower on one end was certainly
grounded (for what it was worth). I only used the arrangement on 40 meters
though so I do not know what the effect might hae been on other bands. My
experience with raised phased verticals without a metal roof were that the
phasing was very difficult and required some substantial iterative testing
to accomplish using some very complicated measuring procedures..
73
Bill W7VP
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <towertalk@contesting.com>
Sent: Thursday, August 17, 2006 2:14 PM
Subject: Re: [TowerTalk] Elevated Vertical with No Radials on Metal Roof
>I had a Butternut HF9V on the 25x45 foot metal roof of my garage about
>12-15 feet off the ground. In order to finesse the bonding issue, I used a
>pair of 125-foot radials that were laid out serpentine fashion to couple to
>each of the sheets of roofing, rather than relying on the inter-sheet
>connection. I didn't have an earth ground connection, but I agree I
>probably should have. I don't know whether the idea of capacitive coupling
>this way has any technical merit, but the antenna worked quite well, and
>even though it was only about 40 feet from the house/shack, no RFI was
>evident when using it in an SO2R setup as the second radio antenna.
>
> 73, Pete N4ZR
>
> At 03:56 PM 8/17/2006, Jim Brown wrote:
>>On Thu, 17 Aug 2006 10:04:43 -0500, ve4xt@mts.net wrote:
>>
>>>You do need to connect the roof to the radial attachment point of the
>>>antenna.
>>
>>>Some things to watch for, however: RFI is one. Have an intermittent or
>>>slightly corroded connection at a seam and you're in for RFI.
>>
>>I agree with all of Kelly's comments, and would emphasize his advice for
>>good bonding together of the various elements of the roof, both to make it
>>more stable (and a more effective ground plane), and to prevent RFI. And
>>also the need for an earth connection for lightning protection.
>>
>>Jim Brown K9YC
>>
>>
>>
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