Are you feeding your antenna against ground? Often it is
easier to start with a dipole in free space first. Try
a 40" wire that is fed in the center. It should show
around 72 ohms at resonance (depending on the wire diameter.)
Then change the frequency to 445 and see what it looks
like. Probably not a perfect match to 50 ohm coax, but
reasonably close. Then look at the radiation patterns
and compare the amount of radiation perpendicular to the
wire.
You can do the same thing using a 20" wire over a ground
plane (or real ground) with similar results.
For the Larsen dual-band antenna, the center loading coil
is self-resonant on 440. This allows it to act effectively
as an insulator between the two halves of the antenna,
and it also causes a 180 degree phase shift from one
end of the coil to the other. This phase shift is
important, because without it the radiation from the
two adjacent half-wave sections would be out of phase,
which is the cause of the lobes in the original dipole
pattern on 440 MHz. So on 440 the antenna consists of
two half waves in phase with the phasing coil between
them. On 2m, each half of the antenna is about 1/4
wave long. The loading coil is at the point of maximum
current/radiation, so it isn't as efficient as a straight
whip might be. The presence of the coil at that point
causes some electrical lengthening of the antenna so it
appears at the feedpoint like a 5/8 wave whip rather
than 1/2 wave, and the matching network at the base of
the antenna is designed to match the antenna to coax on
both bands.
Often you will see a shorter version of this, basically
a quarter wave whip with a small open coil about 1/3 of
the way up the whip. On 440 this is a 1/4 wave radiator
in the bottom, with a phasing coil and a half wave
top radiator (both in phase.) On 2m this is close to
quarter wave resonance, so it is suitable for direct
coax feed on both bands.
Note in both cases that the coil is designed to be self-
resonant on 440. This is an important part of the
design, and isn't obvious if you just look at the turns
of wire as a coil. They are carefully designed to have
the right self-capacitance to make the antenna work.
Here is a good analysis that might help you understand it:
http://www.cebik.com/vhf/cc.html
