It depends.

This is an ideal problem for an antenna modeling program. You should be
able to get a pretty good answer from the free EZNEC demo available at
http://eznec.com.

Roy Lewallen, W7EL

Zommbee wrote:
Hello again,

How close to my 20-meter mono-band vertical could
I put a 15-meter version of the same? I have a great
spot that's only about 10 feet away - will there be
negative interactions of the two? (Of course, it would
be nice if the sun had a few more spots!)

Thanks

Dave WB7AWK