There was a discussion the other day about stub loaded
dipoles. A 30m dipole loaded at each end with a 30m/4
shorted stub is resonant on both 30m and 75m. A 17m
dipole loaded at each end with a 17m/4 shorted stub
is resonant on both 17m and 40m. The stubs provide
inductive loading on the lower bands resulting in
"shorty" dipoles, shrunk by about 20%.

I've summarized two such antennas on my web site at:

http://www.w5dxp.com/dualband.gif
--
73, Cecil http://www.w5dxp.com