It seems plausible when one is first learning about antennas to accept that
you would want to operate with a resonant antenna to develop full power, and
hence efficiency.
But, let us examine the text book treatments of resonance, and invariably
they speak to the condition of resonance as being the equality of magnitude
and opposite sign of the reactances, inductive and capacitive. At the
resonance point, they cancel out.
That is at just one frequency, then you have an antenna that is non resonant
when you operate at various other places on a band, in the usual ham manner
of using antennas.
Now, operating into the non resonant state, you quickly find that the
antenna does not accept as much power as it did at resonance, as the
reactances begin to limit the current the antenna will accept from the
source. This is readily observed by usual ham instrumentation as an overly
high SWR. Most hams will react to correct this and by using a transmatch,
(tuner); the offending reactances will be canceled and resonant conditions
restored for a particular frequency where you operate. Thus, the physically
non resonant antenna CAN receive the same current as the resonant one, and
efficiency is restored.
Since the correction of a non resonant condition is a fairly easy matter,
hams should realize operations with a shorter than resonant antenna is much
preferable to not using an antenna at all. Given insufficient space for a
full size half wave or greater doublet, put up what you can, get a low loss
transmatch and enjoy operations just like the rest.
The new Ten Tec terminated Vee beams are an excellent example of a non
resonant antenna on many frequencies, but with the proper matching will give
excellent gain on the highest bands in the favored direction. In fact, you
could probably operate them without the termination section for
bidirectional use, but the Vee wires would have to be horizontal to give
equal distance front and back from equal angles of take off. In the method
of mounting to one support, highest at the feedpoint, and sloping the wires,
you favor the direction of the slope.
My home made Field Day Vee beams were usually able to work anything you
would hear on 20m and up.
-Stuart
K5KVH
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