Originally Posted by S/V Illusion
The term dipole implies it is cut to a resonant length which would limit you to only a small frequency range. You can construct a multi-band dipole using different resonant lengths of wire fed at a common point as well.
require open wire feed line. You can run coax to the common feed point typically a balun. There are various frequency calculation charts
and formulas all over the internet
for reference. The added benefit is that no tuner should be required.
That's true, but:
1. a multi-band dipole fashioned from different resonant lengths of wire fed at a common point is, IMHO, totally impractical for a marine application;
2. multi-band dipoles can be constructed in several ways, including the one I mentioned: using a balanced feedline instead of coax, and a tuner. This works very well but, again, isn't really practical for a seagoing boat.
3. another way to make multiband dipoles is to use traps. However, these, too, are impractical in the marine environment
1. single-band VERTICAL dipoles are GREAT DX antennas, and work very well in the marine environment, especially for 10 mHz and above. They do not require a tuner, and can take all the power you can feed them.
2. multi-band dipoles -- however constructed -- are not likely to be long-lasting in a real marine environment.
3. the best versatile, all-band antenna for a sailboat is either a random-length wire (like an insulated backstay) fed with an autotuner, or a vertical whip also fed with an autotuner.
On my 42' sloop
I have all three: an insulated backstay with an auto-tuner; vertical dipoles for 20m and 15m; and a stern-mounted mobile whip antenna with resonators for various bands. It's interesting to compare their effectiveness on various bands and over various signal paths...something I've done for several decades.