In my experience, which I have to admit is limited to
the computer screen (!), you have two choices in
designing 2-3 element interlaced yagi's for 10/15
meters:
1) Put the 15 meter driven and reflector entirely
behind the 10 meter antenna.
2) Use a cell type driven element with 1 feedpoint
for both bands (parasitically excite the second
driven element).
I learned all this when planning to add 2 elements
for 15 to my homebrew 3 element 10 meter monobander.
Either approach will work fine. The thing that
doesn't work fine is interlacing the antennas with
the 10 and 15 meter portions laying right on top of
each other - the two antennas interact in very bad
ways.
***dan, K6IF
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