This past weekend was Field day here in the US. We set up our club station NJ2SP as all QRP, all battery/solar power. The CW transmitter made 270 contacts all together on the 80/40/20 and 15 Meter bands. The antenna we used was the EARCHI end fed, which is basically a 53 foot (16 Meters) radiator to a 9:1 UNUN. I used a 25 ft (7.5 Meter) piece of coax between the UNUN and the transceiver to act as a counterpoise.
The whole antenna project is described at:
www.earchi.org/92011endfedfiles/Endfed6_40.pdfAnd a list of wire lengths vs SWR is available at:
http://www.balundesigns.com/servlet/the-102/QRP-9-cln-1-Unun-1.5/DetailThe antenna was used as a sloper, the high end being about 35 ft (10 Meters) up in a tree. Our best DX from New Jersey was Hawaii, Puerto Rico, the Cayman Islands, and the US Virgin Islands, as well as working most of the US West Coast and British Columbia in Canada - all on 5 Watts.
There's no perfect antenna solution for portable QRP operations, but this configuration is fast becoming a favorite!
Larry W2LJ