Kevin Hastings wrote:
I've spent 2 months or so of tweaking an older Cushcraft ATV-5 5-band
vertical with a friend's MFJ analyser and have had this thing exactly where
I want it several times now. After tightening things down and putting vinyl
electrical tape on all traps and section joints (where it seemed to make
sense) it would look fine for a few days to a week.

Then the resonant points of some bands would shift up to no-man's band
seemingly overnight and stay there. I suspected poor screw conections at
the traps, and so have been adding a stainless steel pipe-clamp connection
just above and below the trap for improved connection. Made things better I
thought - now 1-2 bands are just out of whack again.

There's always moisture inside the trap when I disassemble the thing, so I'm
wondering if maybe I shouldn't be trying to tape up the traps at all - maybe
they are retaining water or something that is affecting the capacitance.
Each trap has a drain hole at the bottom, and the aliminium pole itself has
drain holes every now and then that I'm trying not to interfere with.

Is there a trick, or some practical experience here that you can share?

I've had a lot of fun experimenting with this in any case, but winter's
coming...
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Earlier this week I have done a similar exercise with a Butternut HF9V
vertical, using a MFJ259B analyser. Initially I got nowhere,although
nothing was 'visibly' wrong.
However ,when stripping the antenna I found that because of dissimilar
metal corrosion (stainless steel bolts,nuts and washers to aluminium
tubing ) a white aluminium oxyde powder had developed in between the
stainless steel / aluminium contact areas . Following removal of this
and re-fitting all components the antenna can now be adjusted and tuned.
Sofar ,80 metres and 17metres are fine (SWR is around 1.5 : 1) ,the
other bands still to be done. When finished I'll cover all the spots
with above contact areas with (Finnigan's Wax Oil)
This wax oil is widely available in the UK and is primarily meant to
protect the chassis of cars . It is also very suitable for protecting
metal components of antennas especially in coastal areas near salt
water . My QTH is 30 metres (100 ft) from a salt water beach.

Frank GM0CSZ / KN6WH