> From: Keith Dutson
> Your SteppIR must have the complicated matching network to
> work for all bands since element positioning is a compromise
> with the design. This network is lossy.
In fact, the SteppIR does not need a complicated and lossy
matching network. A matching network, other than a combined
un-un/balun is not needed since the proper tuning naturally
matches the antenna.
> By contrast, a Force 12 multi-monoband has no such compromise
> and no associated loss.
You have obviously not modeled any "multi-monoband" antenna
and observed the significant tuning compromises that are
necessary in order to achieve usable SWR on all bands. I have
looked at several commercial designs and by simply removing
the elements for the "other" bands the antenna can be made to
provide significantly more gain (at least one dB) or better
front to rear rejection (at least 5 dB at the design frequency).
Multi-monoband designs are the height of compromise where the
infinitely adjustable antenna is, by it's very nature, capable
of being optimally tuned at any operating frequency.
So long as the elements are tuned properly for their position
in the yagi, the absolute position is relatively uncritical.
For a given boom length, so long as there are enough elements
to maintain the required level of inter-element coupling, the
gain does not vary significantly with the position of the
"inner elements" (elements between reflector and last director).
Front to rear rejection and bandwidth will be effected ... but
as long as the inner elements are not tightly "bunched" at either
end of the boom, F/R is reasonably consistent (+/- 5 dB).
SWR bandwidth is a function of the amount of coupling among
elements and element tuning ... and in an infinitely adjustable
antenna are not critical to the overall performance.
> Give me the Force 12 antenna for simplicity, strength and
> light weight.
You're welcome to your savings of 1/2 square foot and 10 pounds
for the C3 over the 3 element SteppIR. In return, you give up
1 - 2 dB on 20/15/10, 3 dB on 17/12 (as well as a proper match),
operation on 6 meters ... as well as good F/R on 20-12.
... Joe, K4IK
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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