From G3PLX:
I am sure Jim is right to say "it's not quite true..". As I suggested in my
reply to Brian, if a lot of the field lines just 'short-circuit' back to the
top of the tower, then there isn't going to be much contribution from these.
But I think it's possible to believe that if we have a small monopole
sitting in the middle of a square ground area which is the size of the top
of the tower-block, initially at ground-level, and we then raise it by
jacking-up the tower underneath it, our transmitted signal will increase as
we do so.
It's well-known that you can work a lot further by taking a 2m handheld up a
tower, but if you only think of surface-wave propagation theory, you would
say that there wasn't any point in doing the same with a 136kHz 'hand-held'.
If we can accept that the old Post Office work on the field-strength from
ships is reliable (it's the height above the sea that counts, not the height
above the transmitter), and we understand the mechanisms involved, we may
gain quite a lot by taking, not just a small vertical monopole but any sort
of metal object which can be deployed clear of the structure, to the top of
something tall.
73
Peter
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