Re: roof eaves mounted dipole


davidftx <davidftx@...>
 

--- In W5SC@yahoogroups.com, "Town clown" <jpl4097@...> wrote:

I am wanting to know if the aluminum flashing along the top edge of
the roof will affect a dipole ;(or inverted ) as the roof peaks at the
top;
will it absorb any of the signal? I plan to distance the dipole legs
at least 1 ft from the top edge of the roof
Thanks
KE5Bff
Here is a source of great antenna info: http://www.cebik.com/
<http://www.cebik.com/> L.B Cebik died in 2008 and you now have to
register for access but it is free and worth the trouble. Click on
"Tales and Technicals" Start with "Wi're We Using Wire", which deals
with some of your situation.

Rules of Thumbs (and I am all Thumbs):

* Any conductor within 6" to 1" is going to couple with your antenna.
This may be the answer to all you wanted to know. But wait, there's
more.
* Any conductor within 1/4 wavelength is going to affect the pattern
of your signal. This is 1/4 wl in all directions so if the antenna is
above the roof it will be affected by metal in the attic. In an urban
environment is it hard to get 1/4 wl away from all conductive material,
so you do the best you can.
* Antennas less than 5/8 of wl high will be omindirectional. 5/8 of
a wl is about 150 feet high on 80 meters and about 40 feet on 20 meters.
So it makes a difference what band your dipole (or any antenna) is cut
for.
* An Inverted V does not help your signal on the lower bands (but may
help you, if space is an issue) because you are already omnidirectional
(unless you can get up 150+ feet on 80 meters or 75+ feet on 40 meters).
* Higher is almost always better, but is not always possible.
* Getting the antenna up off of the house is helpful. The Loop J.C.
described is affected by his house but is still a very good antenna.
Your dipole will (in the real world) be affected by something. Try to
minimize those somethings by placement of the antenna and relocating
conductive items.
* Trimming your dipole to the correct frequency is worth the time and
trouble. Remember that it is easier to cut off too much wire than it is
to add additional wire to your antenna. The way it looks (electrically)
on the ground will not be the same once it is up in the air. I'm
talking about SWR, resonance, etc. Put it up and measure it. Bring it
back down to cut it.
* If you plan to use a tuner to try to make it work on higher
frequencies, it will only work as low as it is cut. You are not going
to get on 80 meters with a 40 meter dipole. OK you may get a couple of
watts out but the other 98 are gone as heat.

David, K5OLE

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