On 11/7/2024 12:52 PM, Richard Karlquist wrote:
Consider
this: the TH6DXX has 6 or maybe 7 dB gain over a dipole at best. Using
a tuner, the gain will never be less than a dipole. So it will work as
well as a dipole. For casual operation, that may work just fine. It's
only down 1 S unit.
What Rick is getting at here is that element dimensions and spacing is
what determines DIRECTIVITY and pattern IN THREE DIMENSIONS, and those
three setting optimize FORWARD GAIN for those frequency ranges. The
antenna will WORK outside those ranges, but with much less gain. This is
the kind of error you make when SWR is your only criteria. The antenna
"loads," it radiates, but the pattern isn't great.
It's worth spending time with a good modeling program to study this with
the many designs that are included with the ARRL Antenna Book, as well
as Dean Straw's (N6BV) YW software. It plots gain, FB, and, after using
the software to compute a match, SWR vs. frequency, I've used it to
design a few monobanders, built from aluminum and other hardware
scrounged from neighbor hams. I learned how to enter data by studying
the many provided files for designs. There is, no doubt, other software.
This is one I know. I also know and use NEC a lot, but not for Yagis.
73, Jim K9YC
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