Why don't voice radio communications use FM?

"Mxsmanic" wrote in message
...

Some of the words on the cockpit recording are impossible to
understand even today.

Those are not transmitted AM or FM. They are hard wired. This seems to
defeat your point.


In fact, there are several instances of misunderstood radio
communication involved.

You keep mkaing vague references to these instances. Can you cite even one?

On Sat, 02 Sep 2006 16:58:12 GMT, "Steven P. McNicoll"
wrote in
. net:


"Ron Natalie" wrote in message
om...

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


Didn't all early radio use AM?


Early radio, including aviation, used Continuous Wave (CW) modulation
and Morris Code.

Edwin Armstrong patented Frequency Modulation (FM) in 1933.*


* http://en.wikipedia.org/wiki/Edwin_Howard_Armstrong

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.

Analog AM and FM are fundamentally incompatible with each other. Analog AM
and digital encoding over spread-spectrum are fundamentally incompatible
with each other. You asked why AM is being used and not FM and all I'm
pointing out is that if you are willing to consider any new system that is
incompatible with an older system (like FM replacing AM), you may as well
do it with something more advanced and capable, like digital packets over
spread spectrum (which could be considered a relative to FM). One does
_not_ need to implement any of the fancier capabilities that I mentioned. I
stated them only as what could be easily done once the capability is in
place.

Analog cell phones are being replaced with digital cell phones, so I fully
expect the same co-existence can be done with a changeover from analog
aviation radio to digital radio. There would be no need to replace
everything at once and I'm not sure why you think that would need to be the
case.

"Vaughn Simon" wrote:
But changing to FM would require a new radio to be
simultaneously installed in every cockpit in the world. The only way
to accomplish that would be for every plane with a new radio to
transmit in "parallel" (as someone already suggested) for a period of
years on both the new mode and the old mode.

That need not be the case, as evidenced by dual-mode cell phones that allow
access to analog and digital cell sites, though not both at the same time.
Newer radios could certainly be made capable of either mode and a future
cutoff date X years in the future could be set for required switchover when
older model radios would be required to be replaced. This would certainly
ease the transition woes.

Actually, not much does change in aviation compared with other fields of
human endeavor.

It does seem that way. Unfortunately I don't think there is anyone in the
FAA or even the avionics industry who is both sufficiently knowledgeable
about recent advances in communications and has the clout and vision to
push for a radical improvement of aviation communication.

On Sat, 02 Sep 2006 19:51:30 +0200, Mxsmanic
wrote in :

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.

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

Do you use an ANR headset?

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

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.

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

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.

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

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. 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.

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.

On Sat, 2 Sep 2006 14:39:42 -0400, "Peter R."
wrote in :

You are not a pilot, it seems. These claims of yours read as if they are
opinion based on an outsider's perspective, not one who actually has some
hours of aviation radio experience.

It would seem, that Mxsmanic may be one of the "Pilots for 9/11
Truth."

On Sat, 02 Sep 2006 21:06:47 -0000, Jim Logajan
wrote in :

Analog cell phones are being replaced with digital cell phones, so I fully
expect the same co-existence can be done with a changeover from analog
aviation radio to digital radio.

They operate on different frequency bands, so that is not a good
analogy unless you can get the FCC to commit to allocating frequency
spectrum for aviation use.

There would be no need to replace everything at once and I'm not sure
why you think that would need to be the case.

Because it is unlikely the FCC will agree to allocate additional
frequency spectrum for the proposed new communications system.

Larry Dighera wrote:
I would expect to
see data-link equipment (ACARS* or more likely ATN** or NEXCOM***)
available for GA aircraft soon.

* http://en.wikipedia.org/wiki/ACARS
** http://www.tc.faa.gov/act300/act350/
*** http://www.faa.gov/nextgen/nexcom/Publib/aboutnc2.htm

Ah - thanks for the links. The last one states:

"Through the RTCA forum and the FAA's Investment Analysis process, the Time
Division Multiple Access (TDMA) system was selected for implementation. The
TDMA system will use multi channels to operate on one 25 kHz frequency
assignment. The system will utilize Differential (D8PSK) Phase Shift Keying
(D8PSK) and will require a 4.8 KB VOCODER for voice operation. While
current planning calls for operating the system in a 2 -Voice/2 -Data
configuration, other combinations could also be used. Standards for the
system, termed VHF Digital Link Mode Three or VDL-3, are close to
completion and are expected to be validated. In the fully operational
state, the system will accommodate both voice and data."

That would definitely be a great solution, but that page was last updated
January 4, 2000. Do you or anyone else know if any further progress been
made or have the efforts died? (The links I could find all seemed to dead-
end.)

Vaughn Simon writes:

Actually, not much does change in aviation compared with other fields of
human endeavor.

I don't think that is necessarily a bad thing. It does worry me that
the things that change in aviation are things that I'd rather see
stable. 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.

But changing to FM would require a new radio to be
simultaneously installed in every cockpit in the world. The only way to
accomplish that would be for every plane with a new radio to transmit in
"parallel" (as someone already suggested) for a period of years on both the new
mode and the old mode. What are the chances of AOPA allowing that to happen?

I don't see why it would be so objectionable. It isn't even necessary
that the AM be phased out. The FM would simply be available to those
who wish to use it, for the added clarity it provides.

When multiple frequencies are available for the same communication,
you could allocate some to FM and some to AM. Initially all would be
AM. Gradually they'd be shifted to FM as time passes, with plenty of
documentation. Eventually only one AM frequency would be left, which
could be kept active indefinitely.

--
Transpose mxsmanic and gmail to reach me by e-mail.

Jim Logajan writes:

Analog AM and FM are fundamentally incompatible with each other.

Not if they are on different frequencies.

Analog AM and digital encoding over spread-spectrum are fundamentally
incompatible with each other.

Analog AM is used for digital spread-spectrum encoding. AM is the
modulation. Digital is the encoding. Spread-spectrum is just a
frequency and bandwidth assignment.

You asked why AM is being used and not FM and all I'm
pointing out is that if you are willing to consider any new system that is
incompatible with an older system (like FM replacing AM), you may as well
do it with something more advanced and capable, like digital packets over
spread spectrum (which could be considered a relative to FM).

Switching from AM to FM doesn't involve incompatibilities. You can
run both in parallel indefinitely, providing identical services (just
as some commercial radio stations have broadcasts on both AM and FM
simultaneously). Introducing FM doesn't obsolete any of the AM
equipment.

Adding all sorts of digital gadgets is quite a different matter. Now
you are adding functionality that will be available only to the
FM/digital community. This introduces potential safety and usability
issues. Stacking transmissions digitally isn't going to work when the
same transmissions must be mirrored on analog AM--and they have to be
if you want to maintain safety and keep controller workload
reasonable.

One does _not_ need to implement any of the fancier capabilities that
I mentioned. I stated them only as what could be easily done once the
capability is in place.

A change from AM analog to anything else would be glacially slow, and
small steps are safest. I see a direct safety benefit in having the
clarity of FM transmission. I don't see a direct safety benefit in
having other unnecessary features, and I do see potential risks.

Analog cell phones are being replaced with digital cell phones ...

Analog cell phones were replaced with digital well over a decade ago
throughout the world, except for a couple of countries.

There would be no need to replace
everything at once and I'm not sure why you think that would need to be the
case.

The need arises as soon as you add new functionality.

--
Transpose mxsmanic and gmail to reach me by e-mail.