Cecil, W5DXP wrote:
" ***Before they cancel***, they will burn a hole in the black paper
proving that they contain energy."

Anyone who can obtain a copy of Arnold B. Bailey`s "TV and Other
Receiving Antennas" can turn to page 158 to see a diagram of how waves
interfere. Interaction between components of the same signal from two
sources are shown in the figure to produce a combined signal which
varies regularly with the height above the earth. This has a
corresponding effect on the signal received by an antenna placed at a
particular altitude.

The average signal at all altitudes is the same as if there was no
interference. But, that is because the layers of strengthened signal are
exactly offset by the layers of reduced signal strength.

Best regards, Richard Harrison, KB5WZI