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Why don't voice radio communications use FM?



 
 
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  #21  
Old September 2nd 06, 06:45 PM posted to rec.aviation.piloting
Mxsmanic
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Default Why don't voice radio communications use FM?

Peter R. writes:

A leading cause of accidents? Where did you get this statistic?


From the NTSB and several books on the subject.

Guess? If a pilot or controller is not able to comprehend the other side's
transmission, there is no guess. "Say again?" is the phrase of choice and
it is used all over the frequencies.


It's routine in linguistics to unconsciously guess. A person
listening to familiar sounds in a familiar context will "fill in the
blanks" for any sounds that cannot be unambiguously distinguished, and
he will do this without thinking. If he guesses wrong, trouble can
result, and accidents have happened in aviation for this reason (the
most famous probably being the one at Tenerife).

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  #22  
Old September 2nd 06, 06:47 PM posted to rec.aviation.piloting
Mxsmanic
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Default Why don't voice radio communications use FM?

James Robinson writes:

I understand it is because of a characteristic of FM called "capture
effect" that blanks out weaker transmissions when two radios transmit at
the same time. The listener would have no idea that a second, weaker
transmission was being made.


It might be possible to use digital FM and employ anticollision
methods such as those used in other media (networks and so on).
Digital FM would be completely noise free. GSM cellphone technology
already works this way. Also, spread frequency methods such as those
used by GPS can help resolve collision issues, although in aviation
voice communications you really want only one channel speaking at a
time (but I'm sure this could easily be worked out).

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  #23  
Old September 2nd 06, 06:49 PM posted to rec.aviation.piloting
Mxsmanic
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Default Why don't voice radio communications use FM?

Ron Natalie writes:

No actually, it's just historical. Early av radio used AM, and for that
reason we still do.


If that were the only reason, nothing would ever change in aviation.
There must be some reason beyond that. Concerns over safety come to
mind immediately, and ecnonomic issues follow; but in the case of
voice communications, they are so bad already that one can argue that
a newer technology would increase safety more than enough to justify
the initial risk of a new system.

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  #24  
Old September 2nd 06, 06:51 PM posted to rec.aviation.piloting
Mxsmanic
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Default Why don't voice radio communications use FM?

Larry Dighera writes:

Hence the popularity of Active Noise Reduction headsets.


Then why not apply the same logic to the radio channel itself, and
reduce its noise as well.

Do you use an ANR headset?


No. The source of the noise is not anything around me, it's coming
from the channel itself.

Request 'say again' if in doubt.


Most people guess without realizing it, so they cannot do that.

What would you estimate the cost of re-equipping all aircraft with
such a system might be?


They don't all have to be reequipped at once, any more than everyone
must have a glass cockpit.

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  #25  
Old September 2nd 06, 06:53 PM posted to rec.aviation.piloting
Mxsmanic
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Default Why don't voice radio communications use FM?

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.

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  #26  
Old September 2nd 06, 06:54 PM posted to rec.aviation.piloting
RST Engineering
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Default Why don't voice radio communications use FM?

You recall incorrectly.

Jim


"Mxsmanic" wrote in message
...
Steven P. McNicoll writes:

Wouldn't that reduce the available frequencies?


For a given audio bandwidth, FM tends to require somewhat more radio
bandwidth, as I recall,



  #27  
Old September 2nd 06, 07:06 PM posted to rec.aviation.piloting
Stefan
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Default Why don't voice radio communications use FM?

Mxsmanic schrieb:

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


But not because of bad sound quality, but because pilots under pressure
tend to hear what they expect to hear. (A phenomene which does not only
occur with pilots BTW.) These accidents would have happened with hifi
qualitiy radio, too.

Stefan
  #28  
Old September 2nd 06, 07:15 PM posted to rec.aviation.piloting
Mxsmanic
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Default Why don't voice radio communications use FM?

RST Engineering writes:

You recall incorrectly.


Perhaps. Theoretically it should require exactly the same bandwidth,
but I seem to recall reading that typical implementations used more
bandwidth. In any case, you don't need much for voice communication.
The advantage of FM would be the reduction of noise. Digital over FM
would be still better.

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  #29  
Old September 2nd 06, 07:16 PM posted to rec.aviation.piloting
Mxsmanic
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Default Why don't voice radio communications use FM?

Stefan writes:

But not because of bad sound quality, but because pilots under pressure
tend to hear what they expect to hear.


The worse the sound quality is, the more pilots must "fill in the
blanks," and the more likely they are to hear what they want to hear.

If you hear something that could be "five" or "nine," you're much more
likely to choose the number that suits you than you are if you hear
something that is unambiguously one of the two.

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  #30  
Old September 2nd 06, 07:19 PM posted to rec.aviation.piloting
Mxsmanic
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Default Why don't voice radio communications use FM?

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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