W7EL's Antenna current measurements:
This is the overall measurement setup described in the rec.radio.amateur.antenna
newsgroup
on and about November 9, 2003, showing both traces on the oscilloscope. Signal
input is
from an HP 8640B signal generator.
This is a closeup of the inductor and current probes. The upper pipe is the
vertical antenna.
The one to its left is the mounting, which extends about four feet above ground.
The two are
spaced 1/4" apart. The yellow toroid is the inductor being measured. The
smaller black cores
are the current probes. One core of each probe is a transformer, with the wire
carrying the
current to be measured passed through the core's hole. The second core is a
common mode
choke or "current balun", which serves two functions. One is to insure
that no significant current
flows on the outside of the coax cables connecting the probes to the
oscilloscope. The second
is to isolate the probes and reduce any possible capacitive coupling that might
disturb the
measurement. The probe outputs are terminated with 50 ohms at the scope.