On Mon, 16 Aug 2010 19:10:07 -0700 (PDT), Noskosteve
wrote:

It'd also be interesting to probe several points along the feed line.

Anyone see anythhing wrong with this reasoning?

Hi Steve,

You will have the length of the line leading to the probe in the
radiation field and it will disturb the transmission line coupling to
that same field, changing the current characteristics. At some point,
it won't matter, at other points it may matter considerably - the
trick is knowing one point from the other. What will be happening is
that you will force a common mode into a balanced circuit, or will be
further unbalancing an already unbalanced load with that long length
of line.

In other words, it will be a joker in the deck unless you choke that
line too.

The question then comes to this: Why are you doing this? Is this
some form of classroom experiment with what was called Lecher lines?
Measuring SWR? If so, you might find that you are pushing the current
node along the line (like a bead on a string) as you slide the probe.
At some point the node will pop back to its original position and if
you are trying to plot current points, they will exhibit a curiously
distorted shape. This can occur through overcoupling the probe to the
line.

73's
Richard Clark, KB7QHC