making a 40 to 10 end fed half wave resonant on 80m ?

[solaris0121]

Ive been thinking (dangerous I know !)  - I'd like a QRP portable end fed halfwave thats reasonably short - so the 40m band to 10m band ones seem perfect for when I'm out camping and hiking (being about 20 metres long).   Very manageable and easy to sling up over a tree or with a mast.   But I also really want to be able to work 80m as well.......  So now Im wondering is there a way to get a 20metre wire resonating on the 80m band ?

Maybe a bypass switch on the feeder box that ?  maybe a coil that can be switched into the circuit.   If the end is high up wired to a tree then the match box will be closer to the radio, so flicking a switch is quite easy.  So , over to you technical bods to discuss the possibilities !!!  I dont mind a bit of higher SWR, as long as its about 2.5:1 or lower, I can fix the rest with a z match tuner.   Interested to hear your thoughts if something like this is possible.

[gil]

Well, maybe putting an inductance, to be calculated, in the middle of the wire...

Gil.