Richard Clark wrote:
On Fri, 29 Dec 2006 09:04:01 -0500, chuck wrote:

The MFJ-259 has a resolution of one
ohm and the uncertainty of that LSD is probably more than an ohm. You
may not be able to reliably detect small improvements using the MFJ.

Hi Chuck,

This is rather focused at the wrong end of the scale. The antenna's
radiation resistance is going to be lost at the 1 Ohm resolution of
the scale. A 12 foot radiator in the 80M band presents us with about
5 Ohms (a 10:1 mismatch) resistance with so much reactance that it
would wrap the needle around the peg at the wrong end of the SWR
scale.

However, the "lucky" ones may in fact see a SWR that is closer to 2:1,
only to be satisfied that 20 of those Ohms comes from poor
connections, coax, heated coils, and chassis loss. We can all agree
that the MFJ is perfectly capable of measuring 20 Ohms without issues
of error (yes, there will be error, but it won't be focused in the
last digit).

Where will the error be focused?

You will also be able to see that 20 Ohms diminish
TOWARDS the 5 Ohm Rr when you struggle to IMPROVE the situation. Even
if that is everyone's goal, it is rarely achieved; and certainly not
because accuracy foiled them.

73's
Richard Clark, KB7QHC

Hi Richard,

It would surprise me to see a 15 ohm reduction due to incremental
grounding and bonding. I would expect changes in R to be in the range of
a few ohms: right up against the uncertainty of the instrument.

But if he can bond a fender to the hood and see a 15 ohm reduction in
loss resistance, I admit to raising a non-issue. ;-) You and I are
simply expecting different performance results from the incremental
grounding and bonding.

Absolute accuracy is unimportant in this application.

73,
Chuck

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