Larry Dighera writes:

I would guess that noise-blanker and noise-limiting circuits are
incorporated in the current radio designs.

You can't actively remove noise over a radio channel because you have
no unique identifier of noise vs. information. Noise-reduction
headsets work because they know what is noise (outside sound) and what
isn't (audio being played through the headset).

Other than the occasional heterodyne squeal that occurs in the
receiver when two transmitters are transmitting on the same frequency
simultaneously, there shouldn't be any other noise. Ignition noise
should be suppressed by Faraday shielding, and generator/alternator
noise should be bypassed to ground.

Anything that isn't signal is noise. AM transmissions are fuzzy and
hard to hear. In fact, aviation AM radio is probably the noisiest
type of radio voice communication still in use. Most other types of
radio communication today are FM.

What is the nature of the noise you are hearing? Can you describe it?
Is it a hum, pulses, growling, squealing, what?

White noise. It doesn't come from anything within the aircraft or
station.

Regardless of when it occurs, there will ultimately be an additional
cost.

Sure, but one that companies and individuals can assume on a phased
basis at their convenience.

The fact that transponders and VORs exist today (when they did not in
the early days of aviation) proves that this works.

And to expect the old (current) communications system to remain
operational while the new system you are proposing is operating
concurrently won't be feasible if they use the same frequencies.

Presumably they would use different frequencies.

If an new alternate frequency band is used for the new communications
system you are proposing, it could work. But getting the FCC to
allocate additional frequency spectrum will probably be opposed,
because the frequency spectrum is a finite resource, and there are
many more services desiring to use it than there is bandwidth
available.

Aviation is a pretty critical use of bandwidth.

You really should read the information at some of the links I provided
to get an idea of what has been tried, and what is on the FAA's
horizon regarding aviation communications. This topic has been very
thoroughly researched by government personnel and it's unlikely that
you will hit upon a superior system to what the professionals have
examined.

How much of aviation was designed by "professionals"?

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