The diameter is usually not significantly related to the impedance, it
affects Q a lot more.

Impedance is high except at resonance, where it lowers dramatically
(e.g. 500 Ohms to 50 Ohms).

You are asking for trouble with 2 grounds. Any difference in
potential can mean noise. I ground my co-ax on the roof (the mast,
grounded at the bottom) and use the outer conductor for the radio
ground, deep in the bowells of my house.

Technically, I should use a ground lift on the IEC cord, but I don't
unlesss there's a noticeable loop.

On Fri, 11 Jul 2003 21:16:37 GMT, Telamon
wrote:

In article ,
Michalkun wrote:

How does one can determine the impendance of a wire to get the right balun
for it, so it can be hooked up to the coaxial cable?

The impedance of the wire will depend on:

1. The diameter of the wire. The larger the diameter (smaller AWG
number) the lower the impedance will be.

2. The height of the wire above ground. The higher the wire the higher
the impedance will be.

3. The ground conductivity. The more conductive the ground the lower
the impedance will be. Also note here that this is affected by how the
antenna is grounded. If you have just a ground stake or whether you have
radials will make a big difference on how well the wire will perform.
The poorer the ground conductivity the more how you provide grounding
will determine how well the wire will work.

Why grounding is so important is because the wire is just half the
antenna with the ground being the other half. You have to give the RF
some place to go to complete the circuit that is your antenna or it
will not work well.

The coax back to your radio can be that ground but that has the
disadvantage of mixing the antenna currents with the power line noise
at the radios location reducing the signal to noise. One reason why
people are advocates of Baluns is because the antenna can have its own
ground independent of the radio ground.

For a wire antenna one radial run directly under the antenna wire will
do the most good as a minimalist approach.

All that being said a typical wire will be something in the 400 to 600
hundreds of ohms range so the 9 to 1 type of transformer would be the
best type.