In article .com szilagyic writes:
On Jul 23, 10:11 pm, valvejob wrote:

When you join two antennas, the wavelengths are different for the
different channels. Some may cancel each other on your favorite
channel and some may be additive on channels you don't care about.

You can adjust the lengths of the leads going to the two antennas and
change which channels/wavelengths are additive. Try a shorter cable
on one of the two antennas.

This makes sense, but does this apply for antennas that are pointed in
opposite directions? I just want to clarify, you are basically saying
to alter the cable length by say, a portion of a wavelength (a half of
a wavelength?), for one of our favorite channels that is having issues?

Yes, it applies then, too.

You may want to look at the result for frequency cancellation with a good
spectrum analyzer.

Lacking that, and the knowledge of how to understand the results, you
may just have to try things and see how they work.

Alan