I believe the "secret" that Force12 and other more modern designs employ is
to use aggressive steps from one element diameter to the next at the element
tubing joints, instead of the more gentle steps in the old favorites Hygain
and Cushcraft. These big joint steps make the element much less likely to
vibrate. It's possible the large traps on the TH6 helped similarly.
Another problem is the amount of smaller tubing that actually bears against
(inside) the larger tubing. Some Hygain joints (to my recollection) have
very little overlap, so the leverage is poor. This is bad to start... then
if one uses a regular radiator hose clamp, one just doesn't have enough
"squeeze power" on the larger element slits. By the time you've cranked on
the clamp enough, you've often stripped it. The custom clamps that Hygain
used to supply were MUCH better in this regard (though with their big 1/4-20
bolts they are "snag magnets").
Mike N2MG
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I have noticed that most everyone uses rope in the elements to dampen
element vibration, but it is not a cureall. I have used this idea as well,
but have had mixed results. Both my 5 element Hygains (15 and 10) had
serious element vibration, even with the rope. The tips of the elements
would vibrate off within a few months. Never had the problem with my old
TH6DXX.
This isn't just a Hygain problem though, my 6 element KLM 10 meter
monobander had the same problem. My 6 element 15 was just fine. I have had
two Force 12 antennas and have not had a problem even without the rope
trick.
I can still remember the broken element ends on the 5 element Hygain with
the rope hanging out.
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