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Old September 17th 03, 09:44 PM
Mike Coslo
 
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Kim W5TIT wrote:

Newp, sorry. A 40M 1/4-wave dipole can be made to resonate just fine and
work wonderfully. Its position to the ground and center angle have
everything to do with how well it will radiate. And, using a balun or not
doesn't change the whole concept of using a 1/4-wave dipole at any
frequency.

Whether you want them to or not, they work.


A couple points here Kim.

According to the ARRL handbook 2003 edition, chapte 20 page 4:

A fundamental form of antenna is a wire whose length is half the
transmitting wavelength. It is the unit from which many more complex
forms of antennas are constructed and is known as a dipole antenna.

It goes on from there if you want more.

Next I modeled two antennas in EZNEC.

One is a half wave dipole for the middle of the 40 meter band at 7.150
mHz. Each leg of the antenna is approximately 1/4 wavelength long at
65.45 feet. This antenna models out at an SWR of a little over 1.5:1 at
the center frequency, and 2:1 at 7.3 mHz and a touch over 2 mHz at 7 mHz
with the antenna at 50 feet, the take off angle is 35 degrees. All in
all, not too bad an antenna. Most modern rigs will handle the antenna
without a tuner, or simply with their internal tuner.

Next, I modeled a quarter wave dipole for the same frequency and all
other paramaters. With the legs at 32.7 feet, the antenna now displays
somewhat near infinite SWR. The take off angle has now risen to 54 degrees.

That antenna is simply not going to work well at all.

- Mike KB3EIA -



 
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