SOTA / Backpacker-Special
For you folks that hike and mountain-top, here's a full-sized 6-band antenna that really gets out. It can be used on any band from 20m on up to 6m. The MFJ-1979 telescoping-whip adjusts from 27" to 17ft. Just set it at the right length for the band you want to operate on. You'll need a pair of wire radials cut for each particular band you want to operate on. Fishing line (no insulators needed!!) attaches the radials to whatever support you have available (trees, big rocks, etc.). Just remember, those radials will be RF-hot when transmitting!!
The kit fits nicely in a corner of your backpack (except for the 8ft fiberglass "mast" section, which you can use as a walking-stick). You can bungee the mast to whatever vertical support is available, like a fencepost or a small tree. You could use the two radials as "guys" and add two more guys with fishing line, if self-supporting is required. that might be little challenging for one person to set-up, however.
The radials should be at least 6ft off the ground, so you could cut the mast down a little if desired. But the higher the radials, the lower the takeoff angle of the whip. Two opposing radials gives you an omni-directional pattern. I've heard you can run the two radials in the same direction (say about 15-30 degrees apart) and that gives you a lobe with some gain in the direction of the radials. (I have not tried that yet).
Horizontal-radials give you about 70-ohms impedance, and slightly downward-sloping is close to 50-ohms (at resonance). the two elevated radials are the equivalent of 32 ground-mounted radials. Plus, these eliminate the ground-losses.
Trim the 1/4 WL radials equally for resonance. About 24kHz/inch is about right on 20m. The vertical-element tuning is double that at, about 48kHz/inch. The radials do not have to be the exact same length as the center-element. I would use at least 18awg wire.
The pictures show two options for the center-element feedpoint. One is a hose-clamp, but my preferred method is a hole though the mast into a threaded hole in the whip-mount rod, near the bottom.
This baby throws out a nice signal at about 20-degrees, so it's good for DX. On 20m, you'd have to get a full-size dipole up to about 35-40 feet high to outperform it. This antenna will beat just about anything else you can put up out in the field. If you're running QRP, you need a good antenna - and this is it.
