All:
I've noticed that most tri-band Yagi antennas that cover 20,15 and 10 meters
seem to have compromised F/B ratios on the 20-meter band. Some mid-sized
antennas have peak F/B ratios of only 15db on 20M, which isn't terrible, but
that figure is likely to get worse as you sweep across the band.
It must be a necessary trade-off in tri-band design since JK Antennas, Optibeam
and others lean towards the same compromise, which is a shame since one would
want that extra F/B performance on that band.
On average, a 20M mono-band Yagi outperforms the tri-band antenna by 10db or
more, which seems pretty substantial. I'm sure someone in the group has
modeled tri-band antennas like the mid-sized JK and Optibeam, and it would be
interesting to know what the criteria is for the 20M performance trad-off.
Tony -K2MO
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