On 06/03/2010 04:08 AM, -.-. --.- wrote:
Hello,

my mobile setup is composed by a 2 meter vertical whip feeded immediately
close to it by an automatic antenna tuner.

My poor knowledge of antenna systems think that the ATU, choosing the
appropriate LC value, bring the entire system in a resonant condition: true
or false ?
Hello, and that's sort of the ultimate goal. The tuner is designed to
match the antenna type(s) to the source (transmitter) and transmission
line design (characteristic) impedance.

And , second question, because a friend of mine own a MFJ 269 analyzer, how
i can *approximately* have an idea of the efficiency on a frequency F for my
whip ?

The problem here is an impedance analyzer can't distinguish between
resistive losses (antenna, ground, tuner (if considered part of the
antenna)) and the radiation resistance of the antenna. To determine
efficiency you'd have to make some field strength measurements (usually
performed with a calibrated field strength meter) in order to determine
how much of the power going into the antenna terminals is being radiated
into free space. The only "approximation" would be to measure the
resistive part of the antenna feedpoint impedance and then subtract from
this the radiation resistance obtained from calculation. Sincerely, and
73s from N4GGO,
--
John Wood (Code 5520) e-mail:

Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337