Two nearby ASOS broadcasts on the same frequency: Why no squeal?

Peter R. wrote:
For some reason known only to the FAA, both Dunkirk, NY (KDKK), and
Wellsville, NY (KELZ), two small, uncontrolled airports in
southwestern NY state that are about 60 nm apart, share the same ASOS
frequency.

For pilots flying to Dunkirk from the east, retrieving the current
ASOS broadcast is not possible until about 25nm east of the airport,
due to the more powerful KELZ broadcast. This is not so much a
problem when conditions are VFR, but when they are IFR I prefer to
retrieve the ASOS as early as possible in order to choose and prepare
for a particular instrument approach.

In any case, I am curious how it is possible for two transmissions to
be heard over an aviation frequency without the squeal (I forgot the
appropriate technical term for this).

They might just be lucky in that their transmitter oscillators happen to be
so closely matched that the beat frequency is subaudible. Good old AM
modulation!