That's just not true. For a given voice signal, I can squeeze the same
amount of fidelity into an FM channel that I can into an AM channel.

That's the first time I've heard that.

The first time I heard it was when VHF FM at 2 meters became popular in the
early 1960s. The first time I had it explained using Bessel functions was
as a first year graduate student in the late 1960s. The first time I had a
chance to design with it was my first FCC type acceptance gauntlet in the
mid 1970s.

Take a look at a ham 2 meter rig sometime. Channels are 5 kHz. wide.



The current actual transmitted bandwidth of a VHF AM signal is about 4
kHz..

Does that mean the highest audio frequency transmitted it 2kHz?

No, sorry, I should have been absolutely technically precise. The current
actual transmitted bandwidth of a VHF AM signal is plus/minus 4 kHz.. In
practice, with symmetric modulation ("good" AM or FM) you generally give the
bandwidth as the distance from carrier to one sideband and not sideband to
sideband.

The highest audio frequency that we try to achieve is about 3 to 3.5 kHz,
with rapid rolloff above 2.5 kHz. -- generally 12 to 18 dB/octave cornered
on 2.5 kHz.. Yes, there will be some higher order stuff leaking through;
the idea is to contain as much of it as you can in the filter before it hits
the modulator.


Standard deviation on a VHF FM signal is 3.5 kHz.. Bessel and Armstrong
to
the rescue once more {;-)

BTW, the current European channel spacing is 8.3 kHz.. Now THAT's going
to
be a challenge for us AMers to meet.


And, I suspect, it would be completely impossible for FM to fit within
8.3 kHz channel spacing with the same fidelity?

Easier for FM than AM, but it is a moot point. FM will PROBABLY never
happen on the VHF COM band.

Jim