Why don't voice radio communications use FM?

Larry Dighera writes:

I would guess that noise-blanker and noise-limiting circuits are
incorporated in the current radio designs.

You can't actively remove noise over a radio channel because you have
no unique identifier of noise vs. information. Noise-reduction
headsets work because they know what is noise (outside sound) and what
isn't (audio being played through the headset).

Other than the occasional heterodyne squeal that occurs in the
receiver when two transmitters are transmitting on the same frequency
simultaneously, there shouldn't be any other noise. Ignition noise
should be suppressed by Faraday shielding, and generator/alternator
noise should be bypassed to ground.

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.

What is the nature of the noise you are hearing? Can you describe it?
Is it a hum, pulses, growling, squealing, what?

White noise. It doesn't come from anything within the aircraft or
station.

Regardless of when it occurs, there will ultimately be an additional
cost.

Sure, but one that companies and individuals can assume on a phased
basis at their convenience.

The fact that transponders and VORs exist today (when they did not in
the early days of aviation) proves that this works.

And to expect the old (current) communications system to remain
operational while the new system you are proposing is operating
concurrently won't be feasible if they use the same frequencies.

Presumably they would use different frequencies.

If an new alternate frequency band is used for the new communications
system you are proposing, it could work. But getting the FCC to
allocate additional frequency spectrum will probably be opposed,
because the frequency spectrum is a finite resource, and there are
many more services desiring to use it than there is bandwidth
available.

Aviation is a pretty critical use of bandwidth.

You really should read the information at some of the links I provided
to get an idea of what has been tried, and what is on the FAA's
horizon regarding aviation communications. This topic has been very
thoroughly researched by government personnel and it's unlikely that
you will hit upon a superior system to what the professionals have
examined.

How much of aviation was designed by "professionals"?

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Dan Luke writes:

********. One has two syllables, the other only one.

There's a lot more to human speech than syllables. Only a single
phoneme separates the two in many pronunciations (particularly because
restricted bandwidth can limit the intelligibility of fricative
consonants), and that phoneme sounds very much like an unstressed
central hesitation vowel, which means it may not be heard at all.
This is especially true for non-rhotic speakers.

You haven't spent much time communicating via aircraft radios, have you?

How much time have you spent studying phonetics and linguistics? They
are just as relevant here as experience with aircraft radios.

However, I don't think a wealth or dearth of experience in any domain
need be a prerequisite to discussion. And I think it more productive
to discuss the topic at hand than to direct personal attacks at anyone
with whom one disagrees.

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Jim Logajan writes:

...honestly don't make any sense to me. In the first paragraph you see no
problem with two transmitters being used to transmit the same thing using
different frequencies and different modulation techniques, and in the
second paragraph you do.

The second instance involves additional or different information being
transmitted over one channel, but not the other. The first instance
involves only a reduction of noise; the information content is the
same in both channels.

I think you could turn the first paragraph into
the second or vice-versa with appropriate special pleading - which is why
I'm confused about why you find a switch from AM to FM a better transition
than any other transition. I guess I just don't see what you see.

I don't know if it's better than any other transition; I just think
that something should be done to improve the archaic system that
exists now.

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Mxsmanic schrieb:

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 haven't ever actually flown a plane, have you?

Stefan

Emily schrieb:

There were many other steps in the accident
chain, but Tenerife was most certainly not caused by a pilot hearing
what he wanted to hear.

Actually, the KLM captain hearing what he wanted to hear was most
certainly the main cause for that accident.

As a consequence of this misunderstanding, the word "take-off" shall now
only be used in "cleared for take off" and in the read-back of this
clearance, or, at uncontrolled airfields, when a pilot says that he is
taking off. No more "ready for take off", "stand by for take off" and
the like, and no taking off before you are absolutely positively sure
that you have heard and read back the word.

But all this had nothing to do with the readability of the radio
transmissions.

Stefan

On Sat, 02 Sep 2006 20:19:15 +0200, 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.

New systems (P25) already do this type of thing. I develop digital radio
systems. Police, fire, FBI, CIA, DoD, DoE, various municipal
utilities, and various branches of the military are all taking advantage
of this technology. In many cases, the old analog systems must co-exist
with the newer P25 systems. In some cases, more rural analog systems
actually connect with a P25 network via a specialized repeated.
Integration is not a problem.

Last I read, an FAA study indicated they need lots and lots of money
(sorry, don't remember the amount) to upgrade their infrastructure from
analog to digital. The sad thing is, it does not appear Congress is going
to give it to them. Worse, the same report indicates, over the next
10-years, the FAA will exceed their required conversion dollars by simply
maintaining and repair their existing, archaic, analog infrastructure. In
other words, the FAA needs to do something...even if they are simply
updating their existing analog infrastructure. Regardless, the money does
not appear to be available.

Advantages of this technology include:
o call queuing - meaning, PTT places you in a queue so you can get a word
in, even when the controllers are very busy. BTW, this also means no more
"walked on" transmissions.

o call prioritization - All sorts of cool things can be done here -
including, most recent exchange receives priority. Also, should IFR
traffic receive higher priority over that of VFR? What about commercial
traffic? Priority could be adjusted dynamically too. This means
planes in distress could be assigned higher priority. So on and so on...

o hang timer detection - a stuck PTT is not going to lock everyone out

o caller id - imagine your tail number, altimeter, heading, and aircraft
type provided to the controller on every PTT.

o MUCHO better frequency utilization

o Limited data services

The list could go on and on...needless to say, digital has some neat
features.

The only con of digitial compared to analog is reception. With analog,
you can hear a weak signal. It may sound like absoluete crap, but you can
still hear it. With digitial, either you have a strong enough signal to
hear it...and it sounds awesome...or you hear absoluetely nothing at all.

Greg

"Mxsmanic" wrote:

********. One has two syllables, the other only one.

There's a lot more to human speech than syllables. Only a single
phoneme separates the two in many pronunciations (particularly because
restricted bandwidth can limit the intelligibility of fricative
consonants), and that phoneme sounds very much like an unstressed
central hesitation vowel, which means it may not be heard at all.
This is especially true for non-rhotic speakers.

That is why we say "niner." In practice, it works very well to distinguish
nine from five..

You haven't spent much time communicating via aircraft radios, have you?

How much time have you spent studying phonetics and linguistics? They
are just as relevant here as experience with aircraft radios.

One semester in college. My guess is that's a lot longer than you've spent
talking to ATC.

However, I don't think a wealth or dearth of experience in any domain
need be a prerequisite to discussion. And I think it more productive
to discuss the topic at hand than to direct personal attacks at anyone
with whom one disagrees.

When it becomes apparent that an argument is born of ignorance, it is
appropriate to point that out. That is not a personal attack. I did not
impugn your character, merely noted the obvious: WRT aircraft radio
communications, you do not know what you are talking about.

You began this thread with the unfounded assertion that "improper and
misunderstood radio communication is a leading cause of accidents." When
Emily challenged you for evidence, you used the old, lame usenet dodge of
telling her to look it up herself. Since then, you have attempted to create
an argument based on phonetics to support a faulty premise. Your five vs.
niner attempt is the weakest yet, and you would not even have tried it if
you had any experience on the radio.

--
Dan
C172RG at BFM

"Mxsmanic" wrote:

I would guess that noise-blanker and noise-limiting circuits are
incorporated in the current radio designs.

You can't actively remove noise over a radio channel because you have
no unique identifier of noise vs. information.

******** 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.

I'll say one thing for you, you are fearless in your ignorance.

--
Dan
C172RG at BFM

Greg Copeland writes:

New systems (P25) already do this type of thing. I develop digital radio
systems. Police, fire, FBI, CIA, DoD, DoE, various municipal
utilities, and various branches of the military are all taking advantage
of this technology. In many cases, the old analog systems must co-exist
with the newer P25 systems. In some cases, more rural analog systems
actually connect with a P25 network via a specialized repeated.
Integration is not a problem.

So why wouldn't it extend to aviation?

Last I read, an FAA study indicated they need lots and lots of money
(sorry, don't remember the amount) to upgrade their infrastructure from
analog to digital.

They need not upgrade it all at once.

The sad thing is, it does not appear Congress is going
to give it to them.

Congress, like most of America, is hysterical about imaginary human
threats these days, and has probably lost track of the much more
mundane but much more serious safety risks associated with
infrastructure, aircraft, and crews.

Advantages of this technology include:
o call queuing - meaning, PTT places you in a queue so you can get a word
in, even when the controllers are very busy. BTW, this also means no more
"walked on" transmissions.

Do other aircraft hear the transmission when you make it, or when the
controller hears it? Granted, they are only supposed to listen to the
controller, but in practice they will be listening to other aircraft
as well.

How do you make this work in parallel with analog systems that cannot
queue?

o call prioritization - All sorts of cool things can be done here -
including, most recent exchange receives priority. Also, should IFR
traffic receive higher priority over that of VFR? What about commercial
traffic? Priority could be adjusted dynamically too. This means
planes in distress could be assigned higher priority. So on and so on...

It's best not to jump off the deep end with gadgets. Just because
something can be done doesn't mean that it should be done.

o caller id - imagine your tail number, altimeter, heading, and aircraft
type provided to the controller on every PTT.

Where does this leave people with analog equipment?

o Limited data services

What kind of data services do pilots need? Are they going to be
surfing the Web?

The list could go on and on...needless to say, digital has some neat
features.

Neat features aren't necessarily desirable features. There is too
much of a tendency to bloat digital systems with features that have
been hastily designed, inadequately analyzed, and barely tested at
all.

The only con of digitial compared to analog is reception. With analog,
you can hear a weak signal. It may sound like absoluete crap, but you can
still hear it. With digitial, either you have a strong enough signal to
hear it...and it sounds awesome...or you hear absoluetely nothing at all.

If the digital threshold is set where the threshold of intelligibility
would be in analog, there's no net loss.

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"Thomas Borchert" wrote:

Mxsmanic,

I have my doubts about fly-by-wire systems or glass cockpits,
which seem to be increasingly designed for the convenience of
programmers who grew up with Windows rather than for the convenience
of pilots.


Sorry, but that's just plain BS.

He's got a ton of it to spread around.

--
Dan
C172RG at BFM