On my last SOTA Activations I have been using the HyEndFed Qrp 3 Band (40-20-10 meter) wire antenna, and I am very surprised how well it works. The antenna is a half wave for 20 and a full wave for 10 meter, and on 40 it is electrical a half wave.

For more information about the antenna, take a look at :

http://www.hyendcompany.nl