[Elecraft] Real World Antennas

[Ron D' Eau Claire]

Ed, W5EJ, wrote:

> dipole is 2.14db ABOVE an isotropic source.  ...
I would
> hate to see beginners dissuaded from trying verticals without hearing an
> opposing opinion.  In my experience, A     GOOD     vertical over
> a     GOOD
> GROUND SYSTEM     (salt water not required) does an excellent job! ...
> Example:  I have a 40-meter dipole, approximately 1/4-wave above ground,
> (used to have one up 1/2-wave with very little difference noted)
> more or less broadside east and west and a Hy-Gain Hy-Tower
> vertical.

Hi,Ed!

This subject has been discussed at some length on this reflector in the
past, and probably will be again in the future. After all, it takes an
antenna to make a K2 or K1 get out!

Yes, a dipole has 2 db "gain" over an isotropic source (+2 dbi) in free
space, but the situation changes very quickly when you put it in a
real-world environment with the earth nearby.

At about 1/2 wavelength above the earth (assuming a 'typical' somewhat lossy
earth) the gain of a horizontal dipole over a vertical looks very impressive
on paper - something close to a full "S" unit (6 dB) at elevations normally
wanted for DX - and that is comparing a full half wave horizontal with a
full half wave vertical to avoid the issues of additional ground system
losses in a 1/4 wave vertical.

As you point out, such a difference is not always realized in practice for a
variety of reasons. Some of them are not always under our control.

Besides, while 5 or 6 dB sounds like a LOT of difference, it is easily
swamped by changing band conditions. Also, the "gain" of the dipole is off
the sides of the antenna, and that may not be the direction to the station
we are working. Off the ends of the horizontal, both antennas have very
similar performance.

There's a lot more to choosing an antenna than just plugging the numbers
into formulas or a simulator and looking for the desired pattern with the
highest gain. In my experience, it is a worthwhile place to start. When my
antennas don't behave on the air like they did on paper with a large error,
it's time to investigate how my real world antenna is different from the
paper version. That exercise usually yields some new insights.

Ron AC7AC
K2 # 1289