[Antennas] Follow up to RE: length of random wire

Mon, 7 Jul 2003 10:18:43 -0400

Dear Hart,

Others have covered many of the relevant aspects of the problem, such as
good ground, length of dipole, use of a tuner, balanced lines vs. coax, and
so on.

However, there was thing that I inferred from your problem statement that is
troublesome. You mentioned laying a wire on the roof. I would like to point
out very strongly, that antenna wires MUST be as far from ALL objects as
possible - not just conductors or metallic objects and the earth. This goes
for the roof or walls of a house. The reason for this is that the RF energy
will couple into these objects, even wood, to an extent that the bulk of
your RF energy will be dissipated as heat in those objects. Here is my basis
for saying that. I built several different types of antennas for use inside
the loft of a 16' x 16' barn. The results for each and every antenna type
(dipoles, folded dipoles, loop, etc.) were SO BAD in comparison to an
equivalent antenna in the open that I became conviced that there was NO
POINT to an antenna that is in such proximity to energy absorbing obects.

Your next question should be, "how close is too close". Well, that's
difficult to say for certain, but here is a good rule of thumb. If you would
hit anything with it when rotating it around its vertical central axis, it's
to close to the anything. Of course, it's all relative, and as someone is
bound to point out a bad antenna is better than none at all. As bad as they
are, I think I would vote for a Hustler, mobile whip antenna over any of the
wire antennas that you have in mind, simply because you will probably find a
way to mount it so that its coupling into the surroundings are minimal.

Good luck,

Bob Lay in Dahlgren, VA
http://www.qsl.net/w9dmk
----- Original Message -----
From: "Hart Engel" <[email protected]>
To: <[email protected]>
Sent: Monday, July 07, 2003 8:32 AM
Subject: [Antennas] Follow up to RE: length of random wire

> Sorry about that.
>
> I failed to mention its for HF bands [10-80M] on phone operations.
>
> >Lets say for now I have a antenna tuner that I can connect a random wire
> >too. How long should the wire be if I'm just throwing it on the roof of
the
> >house? Can't put a dipole up, or wrap a wire around the water troff, I
live
> >in a semi-detached house. I live in the city and the houses are a spit
> >apart. But the roof is 12ft wide by 20ft long any ideas?
> >
> >Hart
> >
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