... or a sloper (same height) but with the matching unit on the high end (longer feed line)...
Shhhhhhh! If you say that too loudly you're going to upset all those folks who are trying to
claim that there is no current on the feedline with these antennas! (Obviously, if it makes
a difference which end has the feedpoint, then the effect must be due to radiation from
When the 30m band was opened I found there was a significant difference in antenna performance
compared to 40m, which was my favorite band. Relatively low dipoles made lots of contacts out
to 1000 miles or more on 40m, but similar antennas worked poorly on 30m. Vertical polarization
turned out to be better unless I could get the high current portion of the antenna up high enough.
(This is due to the vertical angles of radiation supported by the ionosphere.) The same is true for
20m and higher frequencies, but there it isn't as hard to get a dipole up close to 1/2 wavelength.
The problem with using a sloper from a 20' mast is that, since a half wave is ~46' on 30m, the
antenna will be more horizontal than vertical, and the average height of the portion with maximum
current (therefore contributing maximum radiation) is only 10' off the ground. A better approach
would be to run the wire up at a steeper slope so that there is perhaps 30' of wire leading up to
the top of the mast, with the remainder running off from the top as horizontally as possible. That
will maximize your low angle radiation. (Or just run a wire up the support and feed it against the
truck body as a ground - with a loading coil or a bit of a top hat you can make it resonant.)
Otherwise, find a longer pole, or take a kite with you to hang it from!