On Sun, 7 Jun 2009 19:31:34 -0700 (PDT), dykesc
wrote:

When you said "At the load" I thought you meant at the antenna.

Hi OM,

Quite so, that is the convention.

When
you said "through the line" I thought you meant at the line input
(source end).

Quite so again.

I am measuring at the line input (source end) with both
methods.

I anticipated that.

Are you saying that line length could be a factor in the
quality of the line input impedance measurements?

Very much.

Thanks. Still learning here.

If you were to observe your line distance from the measurement out to
the load, and plot that, you want the line distance to the load to be
some odd-eighth interval of a wavelength long (1/8ths, 3/8ths, 5/8ths,
7/8ths, ... and so on). The reason being that your load Z will be
transformed through that odd eighth to a region on the Smith Chart
that has a milder shift in reactances and resistances for a slight
change in frequency. This means errors of line-length contribution
have a reduced impact on that transform. If you were in quarter
wavelength relationships, those chart lines of reactance and
resistance would change far faster for the same errors in line-length
determination.

This topic is covered at:
http://www.w2du.com/r2ch15.pdf
under the section at:
Sec 15.3 Antenna Impedances From Measured Line-Input Impedances

73's
Richard Clark, KB7QHC