Why don't voice radio communications use FM?

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

The frequency allocation would need to be changed or added to on an
international scope, so I believe the operative organizations would be the
ITU and the ICAO or IATA - the FCC would simply enforce the change within
the U.S. Like you, I would have thought new allocations or changed
allocations would be hard, but changes are made every four years and in the
GHz range they seem to been more readily done; e.g.:

http://www.boeing.com/connexion/news...r_030707j.html

"Mxsmanic" wrote:

With regards to aviation communication, "niner" is the proper phonetic
pronunciation of nine and "fife" is the proper pronunciation of five,
although admittedly "fife" is not as widely used as it should be.

They still sound very much the same.

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

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

--
Dan
C172RG at BFM

Mxsmanic wrote:
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.

Regarding your argument in the paragraph above and the one below...

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.

....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. 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.

"Peter R." wrote:


With regards to aviation communication, "niner" is the proper phonetic
pronunciation of nine and "fife" is the proper pronunciation of five,

There is newsreel footage from the fifties of a nuclear bomb test that
includes scenes from the control room. The guy calling the countdown
actually says "fiver". Talk about unclear on the concept!

--
Dan
C172RG at BFM

Mxsmanic schrieb:

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.

Yeah. One pilot talks on AM and the other listens to FM. Great idea.
Adds a lot of clarity to the communication.

Stefan

On Sat, 02 Sep 2006 21:08:49 GMT, B A R R Y
wrote:

On Sat, 02 Sep 2006 18:03:31 +0100, wrote:


With FM the signal remains much clearer until the point where it
suddenly becomes unreadable when itl becomes weak.

With AM is that readability gradually reduces as the signal gets
weaker. If you open the squelch you can often still read AM when FM
would be unreadable.

That's the way I always understood it. AM transmissions can be pulled
out of background noise. FM is more difficult, as it cuts out before
it's unreadable.

I would imagine digital would be the worst. Digital is either
decodable and there or nothing and silence.

This is all based on my experiences with aircraft AM radios, FM
business radios, broadcast and satellite TV, and radio, so it might
be all wrong. G

You're spot on with your comments. My experience is amateur radio with
AM/FM & SSB plus business radios, broadcast radio & TV FM/AM from
longwave to SHF.

Given the choice SSB gives best low signal readability but not very
suitable for normal aviation. The problem with comparisons is a 10watt
AM transmitter puts out 2x sidebands of 2.5watts (max). All of the
intelligence is available in one 2.5watt sideband, the rest is to make
the signal easier to decode. The equivalent 10watt FM transmittter
uses the full 10 watts but that's getting too technical:-)

At the end of the day if AM equipment is working properly there's not
a problem and there's no reason to change every transmitter in the
world. Probably the main problem is aircraft noise and poor hearing
along with microphone technique and peoples accents! I've flown mamy
aircraft in a number of countries and can't say there's a problem with
AM. More likely to have a problem with a controller rattling out an
instruction too fast. I doubt I've had more than a handful of
transmissions, in 15 years, I'd give worse than readability 4. Almost
always 5.

Normal communication quality is up to 4KHz audio response. As you get
older you loose the high frequencies anyway so forget hi-fi! My
hearing is only good to around 6KHz but when I was younger was around
16KHz. You only require 3KHz audio bandwidth and if pushed for maximum
readability and least bandwidth 2KHz but it sounds very harsh though
very readable.
The worst transmissions in the UK are the military who sometimes sound
like they're using throat mikes. Myself and another aircraft were
working one military controller who was almost impossible to
understand. I could just make him out but the commercial aircraft gave
up. I'd say readability 2.

David

"Dan Luke" wrote:
There is newsreel footage from the fifties of a nuclear bomb test that
includes scenes from the control room. The guy calling the countdown
actually says "fiver". Talk about unclear on the concept!

Maybe he did it because unclear is an anagram of nuclear?

;-)

Stefan wrote:
Mxsmanic schrieb:

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.

Yeah. One pilot talks on AM and the other listens to FM. Great idea.
Adds a lot of clarity to the communication.

Huh? How is that problem different from something transmitting on 121.5 MHz
and someone else listening on 406 MHz?

Why is having multiple channels all using AM not a problem but if one added
more channels using a different modulation now suddenly presenting a
communication problem?

"Jim Logajan" wrote in message
.. .
"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,

The problem I was thinking of that is solved by parallel operation is where
you have two planes in the same pattern who can't hear each other because their
radios are not compatible. The only way I know to solve that is dual (parallel)
operation.

A good example of that concept is what they are doing with TV today. Many TV
stations are transmitting in both analog and digital (HD) so that we are covered
no matter what type of receiver we happen to own.

Vaughn

In article ,
Jim Logajan wrote:


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.)

VDL mode 2 will be coming Real Soon Now. Like all the recent CNS/ATM
mandates/changes (RVSM, 8.33, TCAS, FM immunity, TAWS, BRNAV, RNP-4,
etc etc), the move to VDL is happening way way WAY later than originally
planned by the Big Thinkers.

--
Bob Noel
Looking for a sig the
lawyers will hate