You will find hanging a dipole next to a conductor will couple
heavily... I suspect your cage dipole around the tower will cause you
grief...
There has been lots of discussion on feeding galvanized steel towers
with RF... The consensus is that the surface area of the tower makes up
for it's lower conductivity... There appears to be little/nothing to
be gained by straping a few, small diameter wires to the surface of the
tower...
I have run 160 meter receiving tests where I switched between a steel
quarter wave tower and a sloping vertical wire hung off another tower
240 feet away... Both monopole antennas a resonant quarter wave on
160... Relays used to detune the unused monopole..
There is no difference in the received signal strengths that I can
find... At least for 80 and 160 I have no qualms about feeding the
tower... I used to be a believer in adding wires up the tower face,
but I have found the rapture...
If your tower is grounded and it is more than a quarter wave in height,
you can make it into a folded unipole to allow feeding at the bottom...
This will raise the feedpoint impedence, so you will have to use a
parallel resonant tank circuit to match it... I find this better (in
my twisted mind) than taping a few feet up the tower for a feed
point... ymmv...


cheers ... denny - k8do