a99 or home built ss 102 with ground plane

[fly442]

I have 21' of pipe on side of my 16x80 and going to get a new antenna maby a a99 or imax-2000 the problem is i put a metal roof on my 16x80 would the metel roof cause high swr and other problems.thanks steve

 

[W5LZ]

If your antenna is high enough over that metal roof it shouldn't be a problem. Or, you could mount the antenna -on- that metal roof and use it as a 'ground' How, specifically, would/should you do that? Beats me, try it and see.
- 'Doc

 

[Yankee]

My experience is to not "ground" the antenna to the roof or let the coax ground out, but to get the antenna as close to the metal as possible As in an inch or so. I did something similar with another loaded self contained antenna and grounded to the groundplane, it did not work, but isolated, it worked way better than expected.

 

[W5LZ]

You're right, 'ground' wasn't the best choice of a description. Basically meant to use that metal roof as the so-called 'groundplane'. I don't see how running the feed line on top of that roof would cause any problems. That feed line -is- what's used as the antenna's 'other half', or it's 'counterpoise'/'groundplane' anyway. Any 'coupling' between the metal roof and that feed line would just be 'adding' the metal roof to it's 'other half' to some extent. Considering that any modification of the antenna is defeating it's design, what's the difference?
- 'Doc

 

[Yankee]

I would normally agree with that thinking. It's what I thought at first when I grounded mine, but it does not work at all that way. I do not know the science behind it, but when the antenna is "balanced" with a wire core or some other way to trick the system into thinking it is a 5/8 wave or half wave or whatever, when it's not, just throws it all off. The roof if it is isolated, or my radials, will act as a reflector, but not as part of the groundplane. It will help propagation, but only if it is not grounded to the system. In my case, I just took that ground wire off of any contact with the antenna, in my case a Saturn B-100. Not the whip. With the whip, I did need the ground, since it is not loaded at all, just a wire.

Oh, by the way, there is now about 9 inches of snow out there over the ground and the radials. All I see is that whip sticking up out of the snow. You would think that would ground it out. Well, think again. I used that whip all day today, started talking to Ireland and UK about 8:30 and was still talking to California at 5:30 tonight.