Why don't voice radio communications use FM?

Dylan Smith writes:

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 ...

I certainly hope it doesn't. But knowing Airbus, and its tendency to
install bleeding-edge gadgets on its aircraft in a desperate attempt
to have _something_ that Boeing does not, it wouldn't surprise me at
all if Windows were being used for safety-of-life applications (even
though Microsoft itself recommends against this in the strongest
terms).

... it was probably a general purpose information system that could be used
in flight.

I should think that pilots would have better things to do than type on
a PC. There's enough to worry about in commercial aviation as it is.

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Dylan Smith writes:

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).

Which displays? If it's for safety-of-life applications, it's an
extremely stupid and dangerous idea to use Windows NT.

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Dave Stadt writes:

You neeed to look a litle closer.

Looking closer might be scary, if I find Windows behind any
mission-critical systems.

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writes:

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!

Odd that FM seems to sweep AM out of so many markets, then. All the
FM transmissions I've heard were superior to AM.

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Larry Dighera writes:

But are Avidyne products that employ Windows OS reliable enough to
preclude their negatively impacting air safety?

Nothing that runs a Windows OS is suitable for safety-of-life
applications. This is no reflection on Windows; it's just that the
operating system is designed for general information processing use in
homes, offices, and schools ... not for process control, real-time
systems, or mission-critical applications.

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Larry Dighera writes:

The required level is determined from the safety assessment
process and hazard analysis by examining the effects of a failure
condition in the system.

In other words, nobody actually examines or formally verifies the
code.

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Mxsmanic wrote:
writes:

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!

Odd that FM seems to sweep AM out of so many markets, then. All the
FM transmissions I've heard were superior to AM.

I believe FM's principle advantage over AM is superior immunity to certain
classes of noise - audio fidelity per se should be equal. Here's what my
copy of "The ARRL Handbook for Radio Amateurs, 2002" says about FM:

"The primary advantage of FM is its ability to produce a high signal-to-
noise ratio when receiving a signal of only moderare strength. This has
made FM popular for mobile communications services and high-quality
broadcasting. However, because of the wide bandwidth required and the
distortion suffered in skywave propagation, the use of FM has generally
been limited to frequencies higher than 29 MHz."

Mxsmanic wrote:
Odd that FM seems to sweep AM out of so many markets, then. All the
FM transmissions I've heard were superior to AM.

That's the reason for your error. You are relying on your experience
with broadcast radio, without compensating for other differences.

Broadcast FM has huge bandwidth. (look it up - don't just take it from me)

Broadcast AM has tiny bandwidth. (look that up too)

It is the bandwidth difference that makes broadcast FM look better than
broadcast AM, not the encoding difference.

Think of it this way - they make concrete highways and dirt roads.
Station wagons are allowed only on dirt roads, sedans are allowed only
on concrete highways. I can get from NY to CA much faster in a sedan.

Are sedans inherenly faster?

Jose
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On 2006-09-04, Mxsmanic wrote:
Dylan Smith writes:

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

Are there a lot of GA and commercial formation flights in the air?

That's irrelevant - your assertion was that if there was a controller on
frequency, then pilots only talk to the controller and there is no air
to air communications. This is false, even if there is only ever one
formation flight a year. (In reality, GA formation flight isn't that
uncommon, I've participated in dozens of GA formation flights, many of
which involved communication with ATC, as well as formation takeoffs
from controlled fields).

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On Mon, 04 Sep 2006 17:59:41 -0000, Jim Logajan
wrote:

Mxsmanic wrote:
writes:

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!

Odd that FM seems to sweep AM out of so many markets, then. All the
FM transmissions I've heard were superior to AM.

I believe FM's principle advantage over AM is superior immunity to certain
classes of noise - audio fidelity per se should be equal. Here's what my
copy of "The ARRL Handbook for Radio Amateurs, 2002" says about FM:

"The primary advantage of FM is its ability to produce a high signal-to-
noise ratio when receiving a signal of only moderare strength. This has
made FM popular for mobile communications services and high-quality
broadcasting. However, because of the wide bandwidth required and the
distortion suffered in skywave propagation, the use of FM has generally
been limited to frequencies higher than 29 MHz."

Yes you're correct "audio fidelity per se should be equal" but you
also mention bandwidth, that's critical. There are some advantages
with FM, until the signal gets weak! The other reason for FM is you
can easily modulate the carrier at low level. With AM you need a
higher power modualtor which uses more power.