I asked your for the details of your antenna and measurements, and how
you did your calculations, but I am still left wondering how you have
what appears to be a purely resistive feedpoint impedance and a radiation
resistance of 4 ohms. The second implies a short vertical, and if that is
the case, the first implies some form of loading... but you didn't
mention loading of any kind. Loading, if you have used it, may introduce
an equivalent series resistance at the feedpoint.

Once again, a dansawyer problems leaves us guessing to fill in the
missing dots before attempting to joint them up to make a picture.

Often, solving a problem is about being able to draw the picture, once
the picture is draw, the answer becomes trivial.

Owen

I was also confused by the base of the antenna being 1 meter above
ground, and the radials lying on the ground, or buried. If the base
of the antenna is 1 meter high, then any connection to the radials
is part of the radiation system. Why would you feed the antenna
1 meter up, and not at the base? The antenna is therefore
a ground mounted 5 meter vertical.

NEC predicts an input impedance of 4 - j 1300 with 36 ten meter
radials 1" below an average ground. Loading coils will of course
add to the input impedance.

The measured data are suspect. It would be interesting to know
the length, and type, of coax connecting to the network analyzer.
The return loss of 25 ohms at the end of a piece of coax will be
9.5 dB. Unless the coax is cut to a precise known length it
is unlikely that the phase angle of the return loss will be zero.


Frank.