Why don't voice radio communications use FM?

On Mon, 04 Sep 2006 09:37:53 +0200, Mxsmanic
wrote:

Larry Dighera writes:

You haven't adequately demonstrated the need for a less noisy method
of aviation communications, in my opinion.

I'm not trying to demonstrate need, I'm trying to demonstrate
desirability.

But yours is the
first complaint about white noise present in aviation radio
communications impacting air safety, that I have heard in my 36 years
of being an airman, and I question its validity.

It's not just white noise; it's the poor quality of audio generally.


You don't seem to understand there is NO quality difference in audio
quality between FM & AM, unless you're equipment is faulty and
introducing distortion. I've used AM & FM with amateur radio and been
a professional Broadcast Engineer for 30 years so believe me you are
wrong!

If you compare "like for like" they are both clear and almost
identical quality under normal signal levels. It's only when they
become weak that AM slowly degrades, soon after that point FM will
just stop working.

Don't compare broadcast quality FM with AM. Broadcast FM uses about
15KHz audio bandwidth and likely to be 50KHz or 75KHz deviation, that
gives a channel width of about 130KHz or 180KHz wide (if I remember
correctly) that's why you get low noise in the system. Compare this to
communication quality FM which is likely to have only about 3 to 5KHz
deviation and you'll see a large difference. The bandwidth used is
then much less, but still wider than AM. As I've previously stated an
AM transmitter with 3KHz audio bandwidth has an RF bandwidth of only
6KHz. An FM transmitter using only 6KHz bandwidth will not work as
well as you seem to imply and it requires a wider channel width unless
you reduce the deviation even more and sacrifice the benefits of FM..

Even commercial broadcast AM only uses a narrow audio bandwidth. I'm
not sure but I believe the audio bandwidth of AM broadcast is about
6KHz. On top of that many use very sophisticated audio compressors
which increase the audio level drastically so everything sounds
louder. It means the transmitters are almost fully modulated most of
the time which gives good signal to noise ratio. That helps when
listening in high noise environments like a car. You loose the dynamic
range and distort the signal but it improves readability. Broadcast FM
also uses compression but not as much so less distortion. Classical
radio stations want to retain the dynamic range so should not use
compression.

- snip-

It's hard to put a price on safety. Some people care a lot about it,
some people care very little about it.


Safety is not all about using radios. I've had a transmitter audio
failure within a military controlled area. It was a non-event. Simply
squawked 7600 listened on the receiver and replied with mike clicks.
Got an IFR clearance (even in VFR) and landed with the green lights.

Like others have said this is going nowhere and there are too many
unsupported facts and misunderstandings. If you're a pilot you'll know
AM works well.

"Morgans" wrote in message
...

Even if you got everyone to agree, and pay the money for the new equipment,
the electronics industry could not supply the necessary hardware, except
over a period of a couple years, minimum. In the meantime, we all use
what......?

It would have to be done with dual mode radios, in the same manner that the
cell phone industry made the move from analog to digital and in the manner that
the TV broadcast industry is making that same switch today. Yes, everybody
would have to buy a new radio over a period of just a few years, which is
exactly why I don't expect to live long enough to see it happen.

Vaughn in FL


--
Jim in NC

"Thomas Borchert" wrote in message
...


Oh come on, it's so much fun to jerk the chains of these people ;-)

Yes, but it is important for you to stop and consider; who is the jerker
and who is the jerk? Once you clearly understand, you will stop responding to
trolls.

Vaughn

On 2006-09-02, Mxsmanic wrote:
The reason I ask is that improper and misunderstood radio
communication is a leading cause of accidents, and so it seems that

If you look at the NTSB reports, you'll find that this is not so - in
fact, accidents caused by bad radio communications are so rare, they
barely register as statistical noise! For each accident caused by poor
communication, there are probably thousands of accidents caused by a
pilot flying into weather they cannot handle.

Aircraft fly on the principles of Bernoulli and Newton, not Marconi, and
will fly quite happily with no radio at all, so long as the pilot
remembers to look out of the window and not bang into anything.

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On 2006-09-03, Mxsmanic wrote:
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.

Err... whiskey-tango-foxtrot!?

Of course you're supposed to listen to other pilots. Even when IFR, you
get a picture of what and where the other traffic is so you can think
ahead and anticipate what sort of clearance you're going to get, say,
when entering the terminal area.

Others have pointed out the CTAF so I won't labour that point.
Air-to-air communications is a matter of course, and very useful.

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On 2006-09-03, Mxsmanic wrote:
Emily writes:

All communications are NOT air-ground.

If there is a controller on the channel, they are.

That's incorrect, too. During a formation flight, there will be some
communication between the formation members even when ATC is involved.

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On 2006-09-03, Mxsmanic wrote:
I doubt that they are using VoIP, though, which is notoriously
unreliable.

You're confusing VOIP (voice carried on top of IP packets), which is as
reliable as any other internet protocol with the reliability of a data
stream over the general Internet (note: capital I). VOIP itself is no
less reliable than any other data transmission.

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Mxsmanic,

It's hard to put a price on safety.


You are making the second step after the first. You still haven't shown
how the use of AM radios influences safety. If there is no connection
between AM and safety (and you have shown zero evidence that there is,
even when asked to show it), then it can't possibly enhance safety. So
we're really discussing the price of radios, not of safety.

--
Thomas Borchert (EDDH)

On 2006-09-03, Mxsmanic wrote:
As far as I know (and hope), these cockpits don't have any trace of
Windows running in them. If they do, the situation is much more dire
than I had feared.

I've seen general aviation displays that run Windows NT. They don't have
the Win32 subsystem (which is what really sullies the NT based operating
systems, the actual NT kernel that lies beneath things like the win32
subsystem is quite small and elegant).

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On 2006-09-03, Jim Logajan wrote:
Which ones? (I'd like to know what avionics use MS Windows so I can know
which planes not to get into ;-) )

I recently saw a photograph of the flight deck of the Airbus A380.
Inside, one on the captain's side and one on the FO's side is a pull out
keyboard and display, the display was clearly showing a Windows start
menu. I doubt the PC had anything to do with _flying_ the plane itself -
it was probably a general purpose information system that could be used
in flight. However, it would be amusing if someone loads up Flight
Simulator on the A380 flight deck PCs :-) Or even more amusing, if they
load up Flight Simulator on the flight deck PCs on the Airbus A380
simulator :-)

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