[OKDXA] Dipole Antenna Question

[kd5gho]

Thanks for the Heads up.
Jim
----- Original Message -----
From: "Nelson Derks" <ac5up@vei.net>
To: <okdxa@mailman.qth.net>
Sent: Friday, November 01, 2002 8:53 PM
Subject: Re: [OKDXA] Dipole Antenna Question


> > Yes for a change I am glad I asked.
>
> Since it's going to be a cold and wet weekend, here's a web page you may
> want to spend some quality time with:
>
> http://www.cebik.com/radio.html
>
> > I have read about that type of tuneing, but not in that much detail.
> > The broad banded dipole is a wonderful idea.
> > Their are allot of antenna makers who claim that their product will do
> broad
> > band and don't.
> > The B&W adds a resister to the top of their folded dipole and sey its
like
> a
> > squashed rhombic. bull sh!#.
>
> And here's the analysis of a broadband folded dipole like the B&W:
>
> http://www.cebik.com/wbfd.html
>
> ...which introduces the related concepts of efficiency and gain.
>
> The most efficient antennas tend to be full-size resonant wires as they
can
> couple nearly 100% of the transmit power into the Ether. Throw in some
> tricks, like a loading coil, to make a big antenna more practical in size
> and the efficiency will be reduced. Same for multi-band trap verticals, or
> the terminated folded dipole which relies on a resistor to absorb
reflected
> power that would otherwise trip a newer rig into SWR shutdown. The B&W
> design trades efficiency for bandwidth utility, and that's not necessarily
a
> bad idea if your choice is between something like the B&W or a mono-band
> wire. Better to have a modest signal on several bands than a good signal
on
> one band if that band just happens to be closed tonight. The B&W looks
poor
> on paper when you realize it has no gain (and negative efficiency) over a
> Dipole, but every multi-band wire is a compromise of efficiency and gain.
>
> Which brings us to gain... There is no such thing as free power, but some
> folks think of it that way. Take a VHF Yagi with a rating of 10dB gain. Pu
t
> 50 watts in and it's like 500 watts out. Helluva' deal, but that's in one
> direction only. As long as you can rotate the antenna, and don't mind
> working the rotor box to catch a weak CQ off the back of the beam during a
> contest, you have a good thing going. On HF the antennas are often too
large
> to rotate, so you pick your favorite beam headings and build to match. In
my
> case, the back yard has a longest run that's true North-South. If it were
> East-West, my log would look much different or, I'd become a master of
> compact antenna design. You do your best with what you have to work with,
> and on a city lot with a bad orientation the B&W could be a very practical
> choice...
>
> - AC5UP
>
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