Why don't voice radio communications use FM?

Dan Luke writes:

******** again. I have a radio that does actively remove noise--it has a
button to turn the feature on and off, and it works quite well.

What kind of noise does it remove, and how does it distinguish noise
from signal?

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"Mxsmanic" wrote in message
...
Dave Stadt writes:

Why screw around with FM. It is old technology, not much beter than AM,
and there are much better technologies that would cure the communication
problems and lack of frequency availibility.

Such as?

Such as VOIP actually, or other digital technologies that are now quite
common, cheap, and "off the shelf". In police and fire communications, FM is
quickly giving away to digital modes. My bad for previously talking about FM as
if it were the only possibility.

A digital-capable radio does not care if it is transmitting voice or data, so it
could someday allow truly automated flight control. For example, you might be
able to get clearance into controlled airspace automatically and have it show up
as a green dotted line on your MFD, to be acknowledged with the mere push of a
button.

On Sun, 03 Sep 2006 13:33:36 +0200, Mxsmanic
wrote in :


However, you're not supposed to listen to other pilots; you're
supposed to listen to controllers. All conversations are air-ground,
not air-air.

You'll have to cite a source for this nugget of knowledge. Are you
familiar with Common Traffic Advisory Frequency (CTAF)?

Vaughn Simon writes:

Such as VOIP actually, or other digital technologies that are now quite
common, cheap, and "off the shelf". In police and fire communications, FM is
quickly giving away to digital modes.

I doubt that they are using VoIP, though, which is notoriously
unreliable.

I'm not sure that cheap, common or "off-the-shelf" should be the top
criteria for choosing a replacement for AM radio. I think "safe"
should be the highest priority. If it improves safety, it's good; if
it doesn't, it's bad (unless it can improve something else _without_
compromising safety).

A digital-capable radio does not care if it is transmitting voice or data, so it
could someday allow truly automated flight control. For example, you might be
able to get clearance into controlled airspace automatically and have it show up
as a green dotted line on your MFD, to be acknowledged with the mere push of a
button.

But then you won't need pilots. Actually, it is nearly possible to do
without them today--but radio communication is still one of the
sticking points.

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Larry Dighera writes:

You'll have to cite a source for this nugget of knowledge.

FAA AIMs and CFRs make it pretty clear that communications involving a
controller are pilot-controller exchanges, not pilot-pilot exchanges.

Are you familiar with Common Traffic Advisory Frequency (CTAF)?

Yes, but it and similar schemes don't involve a controller, so
obviously the communication is between aircraft directly.

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"Mxsmanic" wrote:

Dan Luke writes:

******** again. I have a radio that does actively remove noise--it has a
button to turn the feature on and off, and it works quite well.

What kind of noise does it remove, and how does it distinguish noise
from signal?

It removes a lot of the static noise. I do not know the technical details
of how it does it. However, the freqencies of human speech do not cover the
audible spectrum, and all extraneous frequencies may be filtered quite
easily. Even frequencies at the upper and lower ends of human speech may be
filtered with minimal effect on intelligibility. Perhaps it's as simple as
that.

--
Dan
C172RG at BFM

"Mxsmanic" wrote:


However, you're not supposed to listen to other pilots; you're
supposed to listen to controllers.

Utter nonsense.

It will be entertaining to see what bs you come up with next.

--
Dan
C172RG at BFM

"Mxsmanic" wrote in message
...
Vaughn Simon writes:

Such as VOIP actually, or other digital technologies that are now quite
common, cheap, and "off the shelf". In police and fire communications, FM is
quickly giving away to digital modes.

I doubt that they are using VoIP, though, which is notoriously
unreliable.

You should a bit of reading before you make such comments. I happen to be in
the public safety communications field, and we are right now phasing out our old
trunked FM system for a VOIP system. We have already scrapped our old phone
systems in favor of VOIP and that is working just fine. If VOIP were
"notoriously unreliable" we would hardly use it for public safety
communications.

Vaughn

Vaughn Simon writes:

You should a bit of reading before you make such comments. I happen to be in
the public safety communications field, and we are right now phasing out our old
trunked FM system for a VOIP system. We have already scrapped our old phone
systems in favor of VOIP and that is working just fine. If VOIP were
"notoriously unreliable" we would hardly use it for public safety
communications.

Wait and see.

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Dan Luke writes:

It removes a lot of the static noise. I do not know the technical details
of how it does it. However, the freqencies of human speech do not cover the
audible spectrum, and all extraneous frequencies may be filtered quite
easily. Even frequencies at the upper and lower ends of human speech may be
filtered with minimal effect on intelligibility. Perhaps it's as simple as
that.

A noise-reduction system can make some assumptions about what is
_probably_ noise and what is _probably_ signal, but in most cases it
will drop at least part of the signal.

You need at least about 4 KHz for speech, but some sibilants have
components that go as high as 8 KHz or so, and if you chop off the
high frequencies the sibilants may be lost. Thus, 'f' and 's' might
start to sound the same, because the difference between them is in the
high frequencies.

Using fixed phraseology helps a lot, because it is highly redundant.
However, there is still the potential for confusion in relatively
random, non-redundant communications, such as strings of digits or
letters.

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