End Fed Wire (Was NorCal Doublet)
I saw mention of an end fed wire earlier in the discussion. This type of antenna is my 'go to' antenna for portable operation. Whether you want to roll your own or buy one ready made the following is a good site with instructions.
The Emergency Amateur Radio Club, located in Hawaii, builds and sells these to fund their activities but the above link to the instructions is offered as a free download. If you'd like to build your own all of the needed parts are listed.
The instructions say you can go without a counterpoise as long as you use at least 16-20 feet of coax between your tuner and the 9:1 unun. I find that works fine but tuning on 40 Meters is a little touchy. The tuning seems much easier if I attach an extra piece of counterpoise wire that's only about 2 ft long to the provided connection. I am not an antenna modeler, I just know that in my case it makes it easier to tune.
If you substitute a 70ft wire for the antenna, it tunes 80 Meters nicely but isn't as nice of a portable antenna which is my main use. Other wire lengths that should work are found here:
I use this antenna with my Elecraft KX-1 and my Xiegu X108G 20W SSB rig. I usually support the far end of the wire with a 28-foot long Jackite wind sock pole and slope it down to the UNUN which seems to work best if you keep it a couple of feet off the ground.