Reg Edwards wrote:

Dave, I was replying to the original questioner. But by immediately
following your response with mine and including a comment of yours caused a
little confusion. Sorry!

I agree your method will work. The problem, a practical one, is obtaining a
COAXIAL line length exactly an integral number of 1/2-wavelengths long.

The MFJ 259B will measure the length of the line for you before test.
Leave it open circuited and connect the other end to the MFJ. It finds
the 1/2 wavelength frequency.

There's no way of proving it exept by climbing a ladder and disconnecting
the line from the antenna.

A bench setup with a 1 wavelength line does not require climbing and
measuring at the tower.


And it is an exact 1/2-wavelength long at ONE frequency only. But it is
required to make measurements over a whole band of frequencies. To shift to
other frequencies
involves calculations taking Zo into account. But Zo is not accurately
known. So then you have to measure line Zo. And so on.

Agree it is a one frequency measurement.


And you have to know exactly what you are doing because the 259B does not
provide the sign of jX in R+jX.

But, the sign of X is very easy to determine. Increase frequency
'slightly' on the 259B and observe absolute value of X. If X increases
it is inductive. If X decreases it is capacitive. BTW the Or is a value
at antenna resonance only at one frequency. But, you a very well aware
of that. The comment is made for other readers.


But as I said before, all you want to know is whether or not the transmitter
is loaded with 50 ohms. To hell with SWR and antenna input impedance. ;o)
----
Reg, G4FGQ

There is one possibility remaining. If the Yagi is to be tuned for
MAXIMUM gain, and that is the objective, then Ro will be the lowest
value at resonance. Most Ham yagis are not tuned for optimum gain as we
all know.

There is WAY WAY too much emphasis among today's hams regarding low
VSWR. My 75/80 doublet has a VSWR approaching 30:1 and works just FB!!
The problem is the absence of output tuning in most of the rigs
available today. Oh! for my OLD VIKING II or my Drake 4C. grin

Gor Bless and you have my permission to celebrate the USA Father's Day.