Thank You all for the replies.
Ian, what you haved written is what I am trying to do. I have an 80m
dipole up at the moment that needs to be relocated.
I thought I might as well put it up where I could put some 80m traps
inline and extend it for 160m. I haven't got enough room for a half
wave 160m dipole, but I could possibly squeeze in an 80/160m trapped
dipole, depending on how much extra length (with the 80m traps) I need
to add to get it to resonate on 160m. I have since found a drawing for
a 40/80/160m trapped dipole. I will make up the 80m traps from that
plan, add it to my 80m dipole and see how I go.
Cheers
Max