Since the environment in which the antenna is mounted/hung influences
the resonant frequency, I've never been able to see any difference
between insulated and bare copper wire.

As the things have never come out according to the formula, "for me"
I just "cut long and trim to fit".


Nothing wrong with that, trimming and fine tuning to accomodate the
surroundings.

I put up two 75 meter half wave sloping dipoles. They were cut
identical and even used the same make and model of balun. The coax
cable was the same length (LMR-400). Both were mounted at the same
height with the ends the same distance from the tower and ran at the
same angle. One ran to the NE to within about 30 feet of some trees.
The other ran to the south west over an open yard. Both worked well,
but there was between a 50 to 75 KHz difference in the resonant
frequency. The one over the open yard being the higher.


This is 1.3% difference, which I would attribute to capacitance from the trees,
ground variation or something in the vicinity. I would guess that the one
closer to the trees was lower in frequency. I tune my 160 m mobile L loaded
antenna by changing the loading wire slope or distance of the end from the
hood.

I didn't prune them as I use a line tuner to get the full band
coverage any way.


That is fine. The only problem with "plastic" shortening is when you are trying
to build say quad multielement antennas and those 5% can be really annoying. It
is better to know about it and compensate before taking the knife to operate on
the wires. Regular EZNEC can not accomodate "plastic" wires and it is
dissapointing to go through the effort of putting the monster up, only to find
it resonates in the CB band instead of middle of 10m.

Roger Halstead (K8RI & ARRL life member)

Yuri, K3BU