considering building a 9:1 UNUN - a la' the EARCHI ............ here's a chart showing SWRs vs. various wire lengths.
Personally, I use a 53' radiator with a 25' length of coax between the UNUN and the rig, to act as a counterpoise. This setup worked very well for us (SPARC) for Field Day in 2014 and 2015. It has also worked very well for me in various outdoor QRP Sprints.
72 de Larry W2LJ
QRP - When you care to send the very least!