If you wind, say, 100 inches of wire into a coil, it doesn't act the
same as 100 inches of straight wire. And no two different coils wound
from 100 inches of wire will act the same. A coil's radiation
characteristics are very nearly the same as for a wire the outside
diameter and length of the coil, not the length of the wire it's made
from. And the inductance of the coil is dictated by the length, pitch,
number of turns, and diameter of the coil, not the length of the wire
it's wound from. So your question can't be answered unless you tell us
the diameter of the coil and any two of length, pitch, and number of
turns; or the length and diameter of the coil and its inductance at the
frequency at which it's being used.

Roy Lewallen, W7EL

John Smith wrote:
My question(s):

For an example, on the 10 meter band:
If I take a 28" whip and mount it at the end of helical wound coil (wound on
1" diameter form), where the "wire length" of the coil, PLUS, the length of
the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical
length)--BUT, the overall physical length of the antenna (top, tip of whip
to base of helical wound coil) is 1/4 wavelength, what would the radiation
pattern of such an antenna be?

Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the
pattern be a compromise between the two--or, would the pattern be totally
unrelated to either?

What could I expect the impedance of such an antenna be? Would the
reactance be capacitive or inductive? What would be the best way to provide
a match to 50 ohm coax from such an antenna?

What software is available to model such an antenna?

Thanks in advance,
warmest regards