On May 7, 1:03 pm, wrote:

The "tones" you hear at night on MW are heterodynes. IE: the carriers
of various stations clashing with each other. This is due to the
increased
sky wave signals at night. In the day, you have little sky wave, and
most stations you hear are ground wave. Being most are on separate
frequencies, you don't hear many het's...
Het's are a common noise on the CB bands... AM anyway...
Listen to ch 19...Heterodyne city...
You would hear the same thing at 300ghz if two stations were
on the same frequency at the same time. Frequency has nothing to
do with that.

What is the best frequency if I want to listen to distant heterodynes
from outer space?

AFAIK, if the frequency is too high, then you only get line of sight.
Too low, and you can't get signals from space, because the ionosphere
keeps out long-wave signals. Low-frequency signals on earth that reach
the upper atmosphere are bounced back down to the lower atmospheres
because the ionosphere reflects them.