"Barrett" wrote in
:

I've just downloaded EZNEC v. 5.0 demo.
I'm only just starting to learn the basic concepts from the beginning.


Okay Barrett,

One of the basic concepts that is helpful is the "wavelength".

The speed of an RF signal in free space is the speed of light.

Imagine a pure RF sine wave. Starting at zero, the sine will increase to
maximum, then turn around, cross zero again, then go to the other
maximum, and then return to zero. The distance traveled while that
happens is the wavelength. Pretty simple, that, but all the other parts
are related to it. A lower frequency travels further before returning
than a higher one does.

Now in order to have an antenna that will cooperate with our
transceivers, it needs a particular impedence, or near to it. What most
equipment uses is 50 ohms impedence. Some equipment use 75 ohms, but
nothing we're interested in Amateur radio.

So if you are designing a single band antenna that uses coax, you'll want
to hit around that value of impedence.

There is a relationship between the length of the antenna and the
wavelength. In the case of a typical antenna for amateur radio use, the
dipole, you'll end up with around a half wavelength antenna, 1/4
wavelength on each side to get near that impedence. Other antennas may
use more complicated ways of coming up with the proper impedence.

These are generalizations. There are some other aspects, such as changes
in the speed of the RF through cables and insulated wires being different
than in free space, but what I gave you so far is pretty much the basic
basics.

- 73 de Mike N3LI -