Topband: 160 dipole on 80 & 40

[Dick Duccini]

Help - I'm trying to use my 160 dipole on 40 & 80 but I'm unable to tune
it to any kind of resonance.  It's about 260 feet end to end, center fed
with 450 ohm ladder line then to a Nye Viking tuner.  Works great on 160
and ALL other bands.  Any hints as to where to start?  I've already tried
shortening and lengthening it but I'm working in the dark without an
analyzer.
73
Dick
K6VKO