The resulting SWR plot (using Zplot to display plots) looks good on 20m and
gives a better SWR plot than just tuning for best SWR. Also I am getting
about 1dB better on field strength at about 30' from antenna. I suspect it
will be more difficult on the lower bands. My transformer is not perfect
but I am now getting 52 +j0 with it fitted. Using the 1/2 wave of coax
results in errors below about 13.9 MHz and above 14.5MHz but otherwise
matches the readings with the analyzer at the base of the antenna. Just
for fun I made up a full 1/4 wave whip on 20m and tried it out this
afternoon. Much better bandwidth and field strength but looked a bit
ridiculous (and dangerous) on my little Fiat :-)
Dick


"Fred McKenzie" wrote in message
...
In article ,
"Richard Ferryman" wrote:

I have recently acquired an antenna analyzer and have been getting my
mobile
antenna ready for the summer (if we have one!). My procedure has been to
attach the analyzer to the base of the antenna or via 1/2 wavelength of
coax
and tune the antenna to read j0 on complex impedance. This should then
be
correctly resonant. I then look at the real (resistive) part of the
impedanceand use a transformer to match it. For example on 20M the
antenna
reads 35 + j0 so I have a transformer toroidal transformer from 50 ohms
to
35 ohms. This seems to work well.
Question is whether tuning for j0 is going to give a true resonance of
the
antenna? Any other suggestions?

Dick-

I think use of the 1/2 wavelength feed line, with you sitting inside the
closed vehicle, should give you a true resonance reading. Or at least
as close as you can get with the vehicle parked.

My concern is that your matching procedure may be sensitive to frequency
changes. In other words, whatever advantage you have at that one
frequency, may be lost at other frequencies across the band. This might
be especially true on 75 or 40 Meters.

Does your analyzer show SWR? If so, compare a plot of SWR across the
band between your method of matching vs just tuning the antenna for best
SWR at the center of the band.

Fred
K4DII