Why don't voice radio communications use FM?

"Mxsmanic" wrote in message
...
Emily writes:

Really? Can you cite some statistics? I'd be very interested in
reading them.

Just look through accident and incident reports. Radio communication
is one of the weak links in the aviation safety chain.

If you're going to make the claim, point to a viable source of information.
Without providing data, it is just your opinion.

I have read thousands of NTSB reports and don't remember a single one where
the technological limitation inherent in AM radio was a significant cause of
the accident.

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KB

Mxsmanic wrote:
Emily writes:

Really? Can you cite some statistics? I'd be very interested in
reading them.

Just look through accident and incident reports. Radio communication
is one of the weak links in the aviation safety chain.

Has it ever been listed as a probable cause by the NTSB?

"Emily" wrote in message
. ..
Mxsmanic wrote:
Emily writes:

Really? Can you cite some statistics? I'd be very interested in
reading them.

Just look through accident and incident reports. Radio communication
is one of the weak links in the aviation safety chain.

Has it ever been listed as a probable cause by the NTSB?

I have read thousands of NTSB reports and cannot remember one. Could be a
little CRS in there but not much.

"Mxsmanic" wrote in message
...
Emily writes:

Really? Can you cite some statistics? I'd be very interested in
reading them.

Just look through accident and incident reports. Radio communication
is one of the weak links in the aviation safety chain.

--
Transpose mxsmanic and gmail to reach me by e-mail.

I read NTSB reports every day for years. I cannot remember communications
being anything more than down in the noise level as far as an accident cause
and it certainly is not a leading cause of accidents.

"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!

Mxsmanic wrote:
Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio? I
realize there's substantial inertia in the installed base of AM
equipment, but surely one could allocate some new frequencies to FM
and use them in parallel for some years to ease the transition.

If one were to mandate a replacement technology, it would be far far more
effective to use the packet-based mechanisms that digital cellular phone
technology and 802.11 wireless Ethernet (aka WiFi) rely on. Both these
technologies turn over the job of transmission collision resolution to
chip logic and take humans out of the loop. And it is possible to put
audio over WiFi using Voice over IP (VoIP) technology.

Such a system would be incredibly flexible. If one had, say, ten planes
in the air and they all started to talk to ATC at once, a packet-based
system would make it possible to do any of the following:

1) Clearly deliver only one of the voice signals to the controller and
provide a visual display that indicated 9 other planes had attempted to
speak also. It could even provide audio or visual feedback to the other 9
pilots that their transmissions were not delivered - or it could
automatically sequence the delivery of the transmissions to the
controller if the transmissions were not too lengthy.

2) If multiple controllers were available, the audio from several of the
planes could be routed to multiple controllers with no impact on audio
fidelity as far as the controllers or pilots are concerned.

3) Once you go packetized audio, you can put all sorts of useful stuff in
the packets for presentation to the other end - such as aircraft number,
the location and velocity vector from the aircraft's GPS or
altimeter/DG/airspeed indicator, and so on. A pilot could key the mike
and make a request without needing to ID themselves or their position -
that information would be extracted from the audio packet's header and
automatically presented on either a simple display to the controller or
mapped to a fancy map display.

The technical issues have been pretty much solved and commoditized in
both the WiFi VoIP and digital cellular realms. It is my humble opinion
that the radio technology currently being used for aviation
communications is now less reliable and useful than even that used in
home WiFi networks.

Maybe someday the FAA and/or ICAO will consider replacing analog radios
with a more capable digital system....

Jim Logajan writes:

details snipped

Maybe someday the FAA and/or ICAO will consider replacing analog radios
with a more capable digital system....

All very interesting, but one of the criteria that any new system
would have to satisfy is that it would have to work in parallel with
the existing system. Adding features to the new system that are not
available in the old system would create dangerous differences between
the two. Seeing fancy displays in the ATC or tower for the lucky
digital users won't help deal with traffic from old AM users, and it
might even confuse things enough to cause problems.

A highly advanced solution would require replacing everything at once,
which isn't going to happen. A simpler solution that just provides
better quality audio could coexist with older systems without a
problem.

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Mxsmanic wrote:
Jim Logajan writes:

details snipped

Maybe someday the FAA and/or ICAO will consider replacing analog radios
with a more capable digital system....

All very interesting, but one of the criteria that any new system
would have to satisfy is that it would have to work in parallel with
the existing system. Adding features to the new system that are not
available in the old system would create dangerous differences between
the two. Seeing fancy displays in the ATC or tower for the lucky
digital users won't help deal with traffic from old AM users, and it
might even confuse things enough to cause problems.

A highly advanced solution would require replacing everything at once,
which isn't going to happen. A simpler solution that just provides
better quality audio could coexist with older systems without a
problem.

Analog AM and FM are fundamentally incompatible with each other. Analog AM
and digital encoding over spread-spectrum are fundamentally incompatible
with each other. You asked why AM is being used and not FM and all I'm
pointing out is that if you are willing to consider any new system that is
incompatible with an older system (like FM replacing AM), you may as well
do it with something more advanced and capable, like digital packets over
spread spectrum (which could be considered a relative to FM). One does
_not_ need to implement any of the fancier capabilities that I mentioned. I
stated them only as what could be easily done once the capability is in
place.

Analog cell phones are being replaced with digital cell phones, so I fully
expect the same co-existence can be done with a changeover from analog
aviation radio to digital radio. There would be no need to replace
everything at once and I'm not sure why you think that would need to be the
case.

On Sat, 02 Sep 2006 21:06:47 -0000, Jim Logajan
wrote in :

Analog cell phones are being replaced with digital cell phones, so I fully
expect the same co-existence can be done with a changeover from analog
aviation radio to digital radio.

They operate on different frequency bands, so that is not a good
analogy unless you can get the FCC to commit to allocating frequency
spectrum for aviation use.

There would be no need to replace everything at once and I'm not sure
why you think that would need to be the case.

Because it is unlikely the FCC will agree to allocate additional
frequency spectrum for the proposed new communications system.