[antennaware] Q: Extended Double Zepp with tuner and open wire feeders

L. B. Cebik cebik@utkux.utcc.utk.edu
Tue, 3 Nov 1998 06:32:53 -0500 (EST)

The EDZ with parallel line and ATU presents the ATU with a complex
impedance that is dependent on the exact length of the EDZ and the exact
length, Zo, and velocity factor of the line.  The ATU compensates for the
reactance and converts the resistance to the usual 50 Ohms of the line to
the rig.

Since the wire remains at its original length and is the only radiating
element in the system (assuming a normal set-up, its antenna pattern is
unchanged:  the typical main lobe and "ears."

About the only time it makes sense (if ever) to talk about a line "tuning"
an antenna to a different length is in virtual talk.  That is, somewhere
down the line, there is a point at which one can find the low or zero
reactance point and the corresponding low resistive impedance.  However,
this mode of talk is useful only for discussions of impedances on the
line--at most it might help one come close to a point whr one might make a
transition to coax.  The actual radiation from the antenna remains the
same as always--lobe and ears--because the antenna is still the only
radiating element.

For most purposes, it is more straight forward to look at the parallel
line as an impedance transformation device with a continuous
transformation with repetition every electrical 1/2 wl.  THen one can
analyze impedances all the way, rather than possibly confusing part of the
line with part of the antenna.

The sense in which a tuner tunes an antenna is via the compensating
opposite type but equal magnitude of reactance, which, when introduced at
the tuner end, is itself transformed everywhere back up the line to values
equal and opposite the ones already on the line by virtue of the reactance
of the load.  The tuner does not effect any change in the radiation
pattern of the antenna itself.

Hope this helps.



L. B. Cebik, W4RNL         /\  /\     *   /  /    /    (Off)(423) 974-7215
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