That, and the fact that an HVD shows to have a very favorable (i.e., low) radiation angle (see pp 2-11 and 9-10 of 22nd ed. Antenna Book), was what attracted me to that solution.
Basically any vertically polarized antenna will have a similar pattern. If you are really talking
about a half wave
vertical dipole, then feeding it at the bottom against ground (end-fed
) will have exactly the same pattern, since the current distribution along the wire
is the same regardless of where you feed it.
However, if you put up a 40m dipole and want to use it on 20m, then feeding it at the bottom
does NOT give the same pattern as in the center, because the current distribution is different.
However, if the wire slopes at around 45 degrees then it should work better on 20m, though
there will be a bit of directivity to the pattern.
But whether the low angle radiation is actually usable depends on the ground characteristics -
see the next answer.
BTW, being close to the lake, I would expect a high water table under the surface and therefore a very good ground. However, I am not sensing a lot of enthusiasm here and wonder why that is.
Fresh water isn't a good conductor, though it isn't as lossy as some ground types. If the
lake is fresh water it won't be nearly as good as the Great Salt Lake for low angle radiation
with vertical polarization. And if it is salt water, you probably won't have a high water table
in an area with tall trees because they couldn't survive with the salt on their roots.
Even with salt water, the antenna needs to be pretty close to the edge of the water to get
optimum low angle radiation. A couple hundred feet isn't close enough: I use the guideline
that the distance from the edge of the water can't be more than one to two times the
height of the point of maximum current on the antenna above the water. You can also think
of this as you would need to see the water looking down from the point of maximum current
at a 30 to 45 degree angle. Often that means that, if your antenna isn't getting wet from
the spray, it isn't close enough.
If you (you in general) now say "go ahead and try that HVD", then I am back to square one with my ingoing question on how to design the feed line: Ladder line > ? balun ? > coax > [ATU/TRX] ?
Then it becomes a matter of choice. The easiest thing, in my experience, is to build
a half wave dipole fed with coax. You can then string it up vertically or sloping, with
the coax running off over a tree branch at an angle then down to the rig. I tuned up
my backpacking dipole kit ~35 years ago and have used it in many different configurations
since then (vertical, horizontal, sloping, inverted vee, etc.) without a tuner. The
disadvantage of this approach is that you can't use a single wire on both 20m and 40m
without adding traps. A balun at the feedpoint makes performance more predictable,
though I don't use one on my kit to save weight.
You will get a bit more gain on 20m if you use a 40m doublet fed with twinlead or ladder
line to a tuner, providing both bands on a single wire. In that case, run the feedline
to a balanced tuner sitting beside you. Again, such an antenna can be installed in several
Remember, THERE IS NO ONE "RIGHT" ANSWER! It is a matter of personal preference - so
you have to make the ultimate decision of what works best in your situation.
You certainly can try the 20m whip. You can also put a 40m quarter wave wire and tune
it with a tuner on 20m, where it will be an end-fed half wave. (If your tuner doesn't like
high impedances for some reason, lengthen the wire to 40' and use the tuner on both bands.)
You'll want radials with that, of course, just as with the 20m whip.