Why don't voice radio communications use FM?

"Steven P. McNicoll" wrote in message
ink.net...
Didn't all early radio use AM?

Technically, they were probably digital... Dashes and dots... grin

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-.. .. . / -.-- --- ..- -. --.
.-.. . .- ...- . / .- / -.-. ..- - . / .-- .. -.. --- .--

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--. .-. ..- -- -- .- -. ..... ---.. .---- .--.-. --. -- .- .. .-..
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On Wed, 06 Sep 2006 22:50:20 GMT, "Grumman-581"
wrote:

"Steven P. McNicoll" wrote in message
link.net...
Didn't all early radio use AM?

Technically, they were probably digital... Dashes and dots... grin

.-.. .. ...- . / ..-. .- ... -
-.. .. . / -.-- --- ..- -. --.
.-.. . .- ...- . / .- / -.-. ..- - . / .-- .. -.. --- .--

----
--. .-. ..- -- -- .- -. ..... ---.. .---- .--.-. --. -- .- .. .-..
.-.-.- -.-. --- --


You're probably right but putting it into writing with dots & dashes
drives me mad!

After learning morse (up to 20 wpm) about 30 years before getting my
PPL it was easy to ident the VOR's. My instructor was very unhappy
that I would not write down the ID in dots & dashes. Claimed the
iexaminor would not like it. He couldn't believe I found it difficult
to understand morse written as you've done above. Just for fun I tried
to decode your characters, took me a 2-3 minutes to make sense of it.
Much easier to understand as a sequence of musincal type tones :-)

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


"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?

Nope. Used Morse code.
You didn't mean quite that early?




Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Ron Natalie writes:

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

If that were the only reason, nothing would ever change in aviation.
There must be some reason beyond that. Concerns over safety come to
mind immediately, and ecnonomic issues follow; but in the case of
voice communications, they are so bad already that one can argue that
a newer technology would increase safety more than enough to justify
the initial risk of a new system.

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

"Mxsmanic" wrote in message
...
Ron Natalie writes:

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

If that were the only reason, nothing would ever change in aviation.


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

That said, I would really like to see it. It would be great to have enough
frequencies to go around so that you would not have to be constantly mentally
filtering out the transmissions from adjacent uncontrolled airports.

Vaughn

"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.

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.

James Robinson writes:

I understand it is because of a characteristic of FM called "capture
effect" that blanks out weaker transmissions when two radios transmit at
the same time. The listener would have no idea that a second, weaker
transmission was being made.

It might be possible to use digital FM and employ anticollision
methods such as those used in other media (networks and so on).
Digital FM would be completely noise free. GSM cellphone technology
already works this way. Also, spread frequency methods such as those
used by GPS can help resolve collision issues, although in aviation
voice communications you really want only one channel speaking at a
time (but I'm sure this could easily be worked out).

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

On Sat, 02 Sep 2006 14:40:40 +0200, Mxsmanic
wrote in :

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?

I presume the reason stems from AM radio's introduction into aviation
after CW was used prior to and during WW-I. The cost of re-equipping
all aircraft with new radios is also not insignificant.

I realize there's substantial inertia in the installed base of AM
equipment, but surely one could allocate some new frequencies to FM
and use them in parallel for some years to ease the transition.

AM frequencies are currently 25 kHz wide. FM would require more
bandwidth. Regardless, where would you place these newly allocated
frequencies?

The reason I ask is that improper and misunderstood radio
communication is a leading cause of accidents,

What is the source of that questionable statistic?

and so it seems that anything that can make that communication clearer
would greatly improve safety.

Hence the popularity of Active Noise Reduction headsets.

I can barely understand what I hear on the radio.

Do you use an ANR headset?

It is true that the communication is very standardized, making it easier
to guess what is being said, but the results are pretty unpleasant if
one guesses wrong.

Request 'say again' if in doubt.

On a related note, it has occurred to me that one could develop
voice-recognition systems that understand the speech of a pilot and
then repronounce what he says in an extremely standard synthetic
voice.

What would you estimate the cost of re-equipping all aircraft with
such a system might be?

This could also improve understanding, especially for
non-Anglophone pilots who speak with heavy accents. The same systems
could clean up the speech so that it is absolutely standard, with no
missing or added words. Of course, the issue here is that the system
would be stuck if it cannot recognize what is being said, or if a
completely non-standard utterance is made by the pilot. A natural
extension of this would be systems that recognize standard phrases in
one language and translate them to another, but that would be even
more dangerous if the system ever failed.

Pilot: "Oh ****!"

Electronically rephrased: "Mayday!"

Still another idea is special training systems that listen to a
pilot's speech and transcribe it, and point out any problems with
understandability. Again, this would be most useful for
non-Anglophone pilots, but it would work for anyone. If a machine can
understand a pilot's speech clearly, then a human being should
certainly be able to understand it that much more easily.

I can understand you frustration with non-standard phraseology and
foreign accents, but given the current state of the art, such a voice
recognition/synthetic voice system as you suggest would probably be
unworkable not to mention costly and short lived. 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

That's just not true. For a given voice signal, I can squeeze the same
amount of fidelity into an FM channel that I can into an AM channel.

The current actual transmitted bandwidth of a VHF AM signal is about 4 kHz..
Standard deviation on a VHF FM signal is 3.5 kHz.. Bessel and Armstrong to
the rescue once more {;-)

BTW, the current European channel spacing is 8.3 kHz.. Now THAT's going to
be a challenge for us AMers to meet.

Jim




"Larry Dighera" wrote in message
...


AM frequencies are currently 25 kHz wide. FM would require more
bandwidth. Regardless, where would you place these newly allocated
frequencies?