I'll admit, I don't fully understand everything about the 18 HT Hy
Tower, but mine used to be resonant on 80-10 meters until I decided to
"improve" it. I added some radials, as my ground system was pretty
puny, and at the same time, installed the MK160 160 meter kit, which is
the one with a 40 meter trap and longwire to make it into an
inverted-L. To do this I had to swap the 15 and 10 meter stubs, due to
constraints of my yard. Test results were disappointing - the 80
meter resonance has shifted to 4.150 mhz and there is no resonance on
160 either - although the SWR drops to 3:1 at 1.76 mhz, the low end of
my MFJ 249. The rest of the bands are acceptable. I can't see what I
might have done wrong, although anything is possible (even a bad trap,
which the previous owner bought new, and never installed). I can't see
how adding radials should do anything other than improve radiation
efficiency. I did notice that the wire running up the center of the
tower to the 80 meter radiator had a lot of slack for some reason, so I
plan to tip the antenna and replace it. If anyone has other suggestions
on what to look for, or experience in tweaking the MK160, I'd appreciate
hearing from you.
Thanks and 73
Bob W9RAN
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