Why don't voice radio communications use FM?

"Mxsmanic" wrote in message

....that improper and misunderstood radio
communication is a leading cause of accidents,

Cite, please.

... I can barely understand what I hear on the radio.

I suspect the reasons for this relate more to the environmental effects and
quality of the speakers, etc., than to the nature of AM transmissions.

On Sat, 2 Sep 2006 12:02:26 -0400, "John Gaquin"
wrote:


"Mxsmanic" wrote in message

....that improper and misunderstood radio
communication is a leading cause of accidents,

Cite, please.

... I can barely understand what I hear on the radio.

I suspect the reasons for this relate more to the environmental effects and
quality of the speakers, etc., than to the nature of AM transmissions.


The previous comment re capture effect of FM is valid. i.e. the
strongest signal wins. This is desireable for broadcast radio but not
aviation.

With FM the signal remains much clearer until the point where it
suddenly becomes unreadable when itl becomes weak.

With AM is that readability gradually reduces as the signal gets
weaker. If you open the squelch you can often still read AM when FM
would be unreadable.

The audio bandwidth for acceptable communication is 3KHz. When
modulating an AM transmitter you have two sidebands. One up to -3KHz
the other up to +3KHz so transmitted bandwidth is 6KHz.

With an FM transmitter the bandwidth will still be 6KHz plus the
deviation of the system. In addition the sidebands theoretically
extend to infinity but they become rapidly weaker.

To get the best signal to noise ratio with FM you need higher
deviation. If you try increase the number of FM frequencies you need
to reduce the deviation. That in turn would reduce its effectivness.

As for the original comments I would suggest there's something wrong
if AM is not clear.

Could be poor hearing, inadequate headset, turning up the volume
causing overload of either headset or receiver audio. Ignition or
alternator interference distorting the received signal, poor
transmitter, poor microphone, poor microphone technique.
Sorry but the problem is NOT AM!