Bob KC9UR <v32hoosier@...>
For portable operations, some simple efficient antennas can be inexpensively home-brewed. One of my favorites is a 20m half square. If it is end fed, it will resonate on 40m, 20m, 15m and 10m. It has good low-angle gain on 20m and 15m. Mechanically, all it takes is two 18 ft fiberglass push-up poles (or two handy trees), 67 ft of wire, and a 1:49 or 1:64 broadband transformer. Instructions for building the transformer are available on-line in several places (just consists of a ferrite core with a couple windings). End fed half wave (EFHW) antennas are also resonant, very efficient and easy to erect via a handy tree or a fiberglass pole. I've homebrewed and used a 40m/20m/10m EFHW and a 30m/17m EFHW. I've also successfully used commercial EFHW antennas from LNR Precision. Stan Robinson, W9SMR, and I used these (i.e. home-brew half square, 40m/20m/10m EFHW and 30m/17m EFHW) on our APE portable operation last year with good results.
Also even easier to homebrew is a random length wire end fed with a 9:1 unun. The downside of the simplicity is that they require an antenna tuner and are less efficient (i.e. lower gain) than the half square or EFHW (they can also sometimes cause problems with RF on the coax).
Best of luck with your mobile/portable ops!