NEC-LIST: Why coil-load?

Good day all,

The reason I asked about maximum practical Q is that I've
done a couple of examples of coil-loaded whips, and of
course the higher the Q the better the performance. The
first example was a 0.038 wave monoppole on perfect ground.
I chose this because I have a 1973 paper by C. W. Harrison
that gives a table of computed values based on analytical
models. With a Q of 450, base-tuning has an efficiency of
11 % and center-loading has an efficiency of 12.3 %, about a
10 % improvement.

The second example was a wh8ip on a car. The model meets
NEC guidelines and has a good APG values in free space and
over perfect ground. The antenna is 1 m tall, 12.7 mm
diameter, and sits in front of the forward window post. I
intended to tune the antenna for 30 MHz and 90 MHz to cover
the Citizens' and public radio FM bands. The whip has 11
segments and the source is in segment 2. Using just Q=450
coils and tuning for 30 MHz gives an efficiency of 91.6 % at
the source and 91.82 % at segment 5. Using a parallel LC to
tune for both frequencies gives an efficiency of 79.7 % at
the source and 80.13 % at segment 6.

I suppose the 1 m whip is not sufficiently electrically
short that the coil-loading improves its radiation
resistance much. I should try the no-loss case for
interest. Anyway, I conclude from these experiments that
coil-loading is not enough better than base-tuning to
justify the extra fabrication time and cost. Is there a
practical case where the efficiency of a short mobile whip
has been doubled, for instance?

Regards,
Doug Miron

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