On 10/1/2013 1:05 PM, Barry N1EU wrote:
Did you mean to say Force 12 and not M-squared?
Yes, you are right. Sorry. :)
None of the tribanders they tested in 1999 would hold a candle to a
3-element or larger SteppIR yagi today.
Right. But a SteppIR is not a tri-bander, it's an adjustable monoband
Yagi optimized for each band based on its boom length and element
spacing. Because monoband Yagis have no traps and no extra matching
elements, they have almost no loss.
Think about the differences. Tri-banders must use either traps (which
are lossy) or sophisticated matching and tuning elements. The gain of a
Yagi is primarily a function of its boom length as a fraction of a
wavelength and any loss, and secondarily dependent on how well the
designer has optimized it for that length and the band(s) where it needs
to operate. Gain also depends upon the tradeoffs the designer makes for
gain bandwidth, SWR bandwidth, and whether gain or F/B is more important.
It's quite instructive to model stuff like this in NEC, and in the Yagi
modeling software that comes with the ARRL Antenna Book, playing with
element spacing and length and observing what happens to those
performance variables. For example, you can squeeze out another dB or
so of gain if you're willing to give up bandwidth, or F/B.
73, Jim K9YC
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|