On 3/1/2011 5:04 PM, Barry Kirkwood wrote:
> Are you telling us that yagi element spacing has no effect on front to back
I don't think anyone has implied that. But it is quite instructive to
study a decent text like the ARRL Antenna Book, and also to spend some
serious time with good antenna modeling software (like YW, that comes
with the ARRL Antenna Book), trying variations on a design for any given
band. Once you do that, you realize that there are quite a few variables
that can be optimized for various criteria, depending upon what is most
important to YOU. Putting it another way, it is possible to build
antennas with very good performance with a lot of elements, a few
elements, wide spacing, narrow spacing, and so on. For narrow spacings
the optimum lengths will be different that for wider spacing. A design
may be optimized for low SWR over wide bandwidth while sacrificing gain,
gain may be sacrificed for F/B, gain can be maximized while sacrificing
bandwidth of the gain, and so on.
What SteppIR does is pick a single spacing for which they can build an
antenna that can be maximized for gain (and a good match) at every
frequency. That means they don't have to sacrifice gain to get
bandwidth! Yes, it costs more, yes there are more things to fail. But
it can be built with much less weight and wind loading than other
designs that produce equivalent results.
BTW -- any other way to design a multiband antenna can get VERY messy.
If you're not careful, the elements for one band can affect performance
on other bands.
73, Jim K9YC
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