In message , Dave
writes

"maxpower" wrote in message
...
Hello All,
I have an 80m dipole that I wish to use on 160m as well. I am
considering using traps on the existing dipole. I have searched the
web and have not found any 80m/160m trap dipoles. Has anyone added
traps to their 80m dipole to make it usable on 160m? Or could anyone
point me in the right direction towards homebrewing traps to suit. I
have made traps in the past for 40m/80m dipoles but I am unsure what
dimensions, length, turns etc I would need for homebrewing a trap to
make my 80m dipole useable on 80m and 160m.
Thank You.
Cheers
Max

'traps' are normally meant to cut up a big antenna into smaller pieces
for user on higher frequency bands. that is, if you had a 160m dipole
you could put 80m traps in it to make the inner part resonant on 80m.
to get an 80m dipole to resonate on 160m you need to add loading coils
to make it look longer, that will of course make it not resonant on
80m. with some more complex loading and trapping combined you could
probably make something that would force it to resonate on 160m and
80m... but its probably easier to just put a tuner at the radio end and
got with that.

If you already have an 80m halfwave dipole, you will need to add your
80m traps at the ends. Anything added beyond the traps will 'not be
seen' on 80m.

You will then need to extend the dipole beyond the traps, adding
sufficient wire to make it resonant on 160m.

If there were no traps, the additional length of wire needed would be
around 67'. However, below their 80m parallel resonance, the 'effective
inductance' of 80m traps will act as loading coils, and the length of
wire needed will be less than 67'. [Note: The effective inductance will
be greater than the physical inductance of the coil itself.]

How long (or 'short') the additional wire will need to be will depend on
the L/C ratio of the traps. A large L/C will require less additional
wire). You might get away with (say) 30'. If you can't accommodate this
amount of wire, you could always cheat by winding some of it,
effectively as another loading coil.

Note that, because your 160m dipole has inductive loading (from the 80m
traps alone, plus any additional loading you have to add), it will have
less bandwidth than a full-size 160m dipole.

Of course, an easier alternative approach might be simply to use an open
wire feeder, and a tuner in the shack. The existing 80m dipole will be
reasonably efficient on 160m as it is, but it could be improved by
extending the existing dipole (assuming you have the space available).
--
Ian