If you add a little series inductance at the feedpoint of the 40 meter
dipole, it'll load fine as a 3/2 wave on 15 meters. You can convert the
cloverleaf pattern on 15 to a bidirectional pattern with some gain,
without much effect on 40, by moving the wires together horizontally,
each by 30 degrees, for a 120 degree included angle -- if you have room,
and if you'll settle for essentially two-direction operation on 15.

But whether you use that scheme or not, a combined 40/15 meter dipole
and separate dipole for 20 should work well. I wouldn't put them in
parallel, but would hang the 20 meter antenna under the 40/15 as an
inverted vee, or separate them horizontally. That will make the
arrangement less critical to tune, and improve the bandwidth of at least
the 20 meter antenna.

Roy Lewallen, W7EL

Steve wrote:
I have a span of approx 32 ft. to use for a horizontal dipole. It will
be about 40 ft high.

I want to use 2 parallel wires to cover 40M, 20M, and 15M. Ladder line
is not feasible here, so I need to tune the antenna for min SWR to
minimize coax feedline losses.

I would use 1 of the wires for 20M as a 1/2 wave dipole; and use the
other for 40/15.

The 40/15 will have off center loading coils at approx 11' on each
side (so it will be a 1/2 wave dipole for 15M), followed by more wire
to use the span. The coils would be designed to tune the whole span
for 40M, using either the Hamcalc program or one of the G4FGQ
programs.

Is the combined 40/15 element a reasonable idea? Or should I use
seperate wires for 40 & 15M?

I expect the interaction with the 20M wire will require several
pruning iterations.

Thanks in advance for any helpful comments.

73
Steve
K8SDK