Try suspending the measuring instrument in mid-air to remove your body
capacitance and see if it makes any difference to the measured
impedance.
----
Reg

Reg Edwards wrote:
Try suspending the measuring instrument in mid-air to remove your body
capacitance and see if it makes any difference to the measured
impedance.

Suspending the analyzer might be adequate for 6 meters, which is the
antenna under discussion. But I should mention for the benefit of the
general audience that it isn't adequate for 2 meters. Not too long ago I
heard from an EZNEC user who found a substantial difference between
modeled and measured results from a simple antenna. On my suggestion, he
added a simple wire frame representation of the MFJ 269 to his model,
and it made the model results much closer to his measurement. So in that
case the antenna analyzer itself was enough to substantially skew the
measurement.

Roy Lewallen, W7EL

The Autec Analyser is a better instrument than the MFJ for
suspended-in-mid-air measurements. It is much smaller and is lighter
in weight and has a smaller capacitance.

The Autec case has a self-capacitance of the order of 3 pF
corresponding to a reactance of 1768 ohms at 30 MHz which can be
ignored when measuring 50 ohms with zero lead length.

The Autec's highest frequency is 35 MHz.

The MFJ's highest frequency is at VHF. With a self-capacitance of 7
pF at VHF substantial errors can occur.

To estimate capacitance, the DC capacitance of a sphere is -

pF = 55.55 * Diameter in metres.
----
Reg.

Reg wrote, "Try suspending the measuring instrument in mid-air to
remove your body capacitance and see if it makes any difference to the
measured impedance."

Even better (perhaps), set up the antenna as you plan to use it,
including balun and feedline. Make your measurements at the "other"
(non-antenna) end of the feedline. Back out the effects of that length
of feedline, and you have the antenna feedpoint impedance in that
particular environment. If the line is reasonably long so you and your
measurement device are at least a couple wavelengths from the antenna,
and reasonably well decoupled from the antenna so that there isn't a
lot of "antenna current" on the feedline, your measurements should be
essentially independent of your presence and the presence of the
analyzer.

Cheers,
Tom