On Sat, 22 Aug 2009 15:49:14 +0100, "barett"
wrote:

I am causing TVI at the moment and I was told that if I insulated the beam
from the mast and choked the coax just below the beam it would guarantee to
solve my TVI problem and improve the efficiency of the antenna.

Stop listening to those people who "told" you this and "guarantee"
(whatever that means) it as a solution.

TVI is most frequently caused by your feedline's proximity to RF
sensitive devices AND the presence of Common Mode currents on the
feedline. Put a choke on the transmission line at the feed point and
another choke one quarter wavelength away from the feed point towards
the transmitter.

This is a very common topic here and if you were to Google the group's
combined postings about it, you would find a world of education that
goes beyond this simple prescription. (Google the terms TVI and
Common Mode and Choke.)

73's
Richard Clark, KB7QHC