On Tue, 13 Jun 2006 07:05:51 GMT, Owen Duffy wrote:
Just think of the antenna as the "source" and consider its
characteristic Z. Now consider the common mode circuit of the
transmission line and its Z. So often this is an unknown, and if we

Richard, does Z mean the characteristic impedance of the line in the
"differential" mode or "common" mode?

Hi Owen,

It occurred to me that there are two Zs mentioned and you did not
really differentiate as I had.

The antenna Z will be something we all have expectations of attaining,
and we quite often measure it. For the dipole we merely assign a
value of 70 Ohms for this discussion.

Now, we have the Z of the "third wire" which is almost never measured,
especially for every application. If it presented an equal 70 Ohms,
it would then hog half the power - however, this is unlikely in the
scheme of things. Let us just say it will exhibit some value that may
tend to absorb and radiate power. This capacity both upsets antenna
patterns and contributes to RFI and feed line radiation.

If the source is 70 Ohms and we add 200 to 700 Ohms of resistivity in
line (through the application of ferrites as common mode series
resistances), then we have diminished its capacity to hog power. As
1000 Ohms of ferrite resistance is easily applied, this has generally
satisfied many conditions.

73's
Richard Clark, KB7QHC