Why don't voice radio communications use FM?

On Sun, 03 Sep 2006 13:39:09 +0200, Mxsmanic
wrote:

Larry Dighera writes:

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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.


This thread is becoming a lot of guessing and not based on facts!
I doubt anybody has evaluated AM compared to FM in an aircraft so
won't know what the effects are when tried side by side.

There is absolutely no difference in qualilty between AM & FM if they
are designed to the same specification. If you modulate an AM or FM
transmitter with up to 3KHx of audio they will sound identical. What
you put into the transmitter comes out of the receiver assuming there
isn't a fault.

FM maintains a low background noise longer than AM and the only
difference is at low signal levels when FM very quickly becomes
totally unreadable. AM can still be heard and understood, depending on
the ability of the person listening. With all the noise in an aircraft
a little bit of low level background noise is not significant.

Digital has some merit but again when the signal reaches a threshold
it stops completely.

The whole thread is futile as the centre of the 'aviation universe'
may well be the US but you aren't going to get the rest of the world
to change. Even having regultions which are supposed to be accepted
worldwide doesn't work. Most counties have exceptions.

About the only thing which is standard is the use of the English
language. Even then the locals will use their own language! Have you
ever worked controllers with Spanish English, Finnish English,
Canadian English, New Zealand English, Cyprus English, Bahamian,
Caribbean or even Amereican English. That's where the differences can
be heard. AM radio is adequate for the job and if you don't think so
then get your installation checked out by a qualified engineer, you
may be suprised.

As for increasing the number of frequencies Europe has introduced
8.3KHz spacing. Fortunately at the lower GA flight levels it's not
required but the higher commercials now require new radios.

Most radios are dual NAV/COM so not only would you need a new COM but
a new NAV too... It isn't going to happen...!