Why don't voice radio communications use FM?
Mxsmanic
communications for aviation use FM radio instead of AM radio? 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.
The reason I ask is that improper and misunderstood radio
communication is a leading cause of accidents, and so it seems that
anything that can make that communication clearer would greatly
improve safety. I can barely understand what I hear on the radio. 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.
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. 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.
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.
--
Transpose mxsmanic and gmail to reach me by e-mail.
Steven P. McNicoll
"Mxsmanic" <mxsm...@gmail.com> wrote in message
news:ojuif2pidfigcdn85...@4ax.com...
>
> Perhaps this is a naive question, but: Why don't voice radio
> communications for aviation use FM radio instead of AM radio?
>
Wouldn't that reduce the available frequencies?
Peter R.
> The reason I ask is that improper and misunderstood radio
> communication is a leading cause of accidents,
A leading cause of accidents? Where did you get this statistic?
> but the results are pretty unpleasant if
> one guesses wrong.
Guess? If a pilot or controller is not able to comprehend the other side's
transmission, there is no guess. "Say again?" is the phrase of choice and
it is used all over the frequencies.
--
Peter
James Robinson
> Perhaps this is a naive question, but: Why don't voice radio
> communications for aviation use FM radio instead of AM radio?
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.
With AM, when two radios transmit on close frequencies, you either hear
both signals poorly, or you get squeal, which is the sum of the two
signals. This characteristic is considered important when you have elevated
transmitters that can be hundreds of miles away, like on aircraft.
Larry Dighera
wrote in <ojuif2pidfigcdn85...@4ax.com>:
>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 shit!"
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
Emily
> The reason I ask is that improper and misunderstood radio
> communication is a leading cause of accidents
Really? Can you cite some statistics? I'd be very interested in
reading them.
RST Engineering
swap basis) the VHF com band for stuff up between 600 and 900 MHz. that have
very limited usage. Not only could we get way more bandwidth, but the
antenna size is cut by a factor of 6 or so.
Jim
"Steven P. McNicoll" <ronca...@nospamearthlink.net> wrote in message
news:v%eKg.5158$bM....@newsread4.news.pas.earthlink.net...
John Gaquin
> communication is a leading cause of accidents,
Cite, please.
>... I can barely understand what I hear on the radio.
I suspect the reasons for this relate more to the environmental effects and
quality of the speakers, etc., than to the nature of AM transmissions.
RST Engineering
signals are widely differing in power (google "AGC" or "AVC" for an
explanation). The odds of two signals being absolutely equal in time is
close to zero. True, they can start simultaneously, but the ending time is
generally measured in multiseconds. One side or the other always gets the
tag end of one conversation or the other and can figure out that a second
station is trying to get a message across.
The squeal when two nearly equal power signals is not the sum of the
frequencies, it is the difference.
Jim
"James Robinson" <was...@212.com> wrote in message
news:Xns98325DCEA9A...@216.196.97.142...
John Gaquin
"James Robinson" <was...@212.com> wrote in message
> With AM, when two radios transmit on close frequencies, you either hear
> both signals poorly, or you get squeal, which is the sum of the two
> signals. This characteristic is considered important when you have
> elevated
> transmitters that can be hundreds of miles away, like on aircraft.
Sounds plausible. Marine radios also operate in the VHF band, but are FM.
They are also almost always at or very close to sea level.
RST Engineering
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" <LDig...@att.net> wrote in message
news:dcvif2p93dil148cv...@4ax.com...
Larry Dighera
>> AM frequencies are currently 25 kHz wide. FM would require more
>> bandwidth. Regardless, where would you place these newly allocated
>> frequencies?
>
On Sat, 2 Sep 2006 09:10:19 -0700, "RST Engineering"
<j...@rstengineering.com> wrote in
<W%hKg.53$sa1.1...@news.sisna.com>:
>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.
That's the first time I've heard that.
>The current actual transmitted bandwidth of a VHF AM signal is about 4 kHz..
Does that mean the highest audio frequency transmitted it 2kHz?
>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.
>
And, I suspect, it would be completely impossible for FM to fit within
8.3 kHz channel spacing with the same fidelity?
Bob Noel
"RST Engineering" <j...@rstengineering.com> wrote:
> BTW, the current European channel spacing is 8.3 kHz.. Now THAT's going to
> be a challenge for us AMers to meet.
huh? Putting FM into 8.33 kHz spacing? or did you mean something else?
--
Bob Noel
Looking for a sig the
lawyers will hate
RST Engineering
>
>>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.
>
> That's the first time I've heard that.
The first time I heard it was when VHF FM at 2 meters became popular in the
early 1960s. The first time I had it explained using Bessel functions was
as a first year graduate student in the late 1960s. The first time I had a
chance to design with it was my first FCC type acceptance gauntlet in the
mid 1970s.
Take a look at a ham 2 meter rig sometime. Channels are 5 kHz. wide.
>
>>The current actual transmitted bandwidth of a VHF AM signal is about 4
>>kHz..
>
> Does that mean the highest audio frequency transmitted it 2kHz?
No, sorry, I should have been absolutely technically precise. The current
actual transmitted bandwidth of a VHF AM signal is plus/minus 4 kHz.. In
practice, with symmetric modulation ("good" AM or FM) you generally give the
bandwidth as the distance from carrier to one sideband and not sideband to
sideband.
The highest audio frequency that we try to achieve is about 3 to 3.5 kHz,
with rapid rolloff above 2.5 kHz. -- generally 12 to 18 dB/octave cornered
on 2.5 kHz.. Yes, there will be some higher order stuff leaking through;
the idea is to contain as much of it as you can in the filter before it hits
the modulator.
>
>>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.
>>
>
> And, I suspect, it would be completely impossible for FM to fit within
> 8.3 kHz channel spacing with the same fidelity?
Easier for FM than AM, but it is a moot point. FM will PROBABLY never
happen on the VHF COM band.
Jim
Ron Natalie
> Mxsmanic <mxsm...@gmail.com> wrote:
>
>> Perhaps this is a naive question, but: Why don't voice radio
>> communications for aviation use FM radio instead of AM radio?
>
> 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.
>
reason we still do.
Steven P. McNicoll
"Ron Natalie" <r...@spamcop.net> wrote in message
news:44f9b61d$0$24183$9a6e...@news.newshosting.com...
>
> No actually, it's just historical. Early av radio used AM, and for that
> reason we still do.
>
Didn't all early radio use AM?
NOS...@easily.co.uk
The previous comment re capture effect of FM is valid. i.e. the
strongest signal wins. This is desireable for broadcast radio but not
aviation.
With FM the signal remains much clearer until the point where it
suddenly becomes unreadable when itl becomes weak.
With AM is that readability gradually reduces as the signal gets
weaker. If you open the squelch you can often still read AM when FM
would be unreadable.
The audio bandwidth for acceptable communication is 3KHz. When
modulating an AM transmitter you have two sidebands. One up to -3KHz
the other up to +3KHz so transmitted bandwidth is 6KHz.
With an FM transmitter the bandwidth will still be 6KHz plus the
deviation of the system. In addition the sidebands theoretically
extend to infinity but they become rapidly weaker.
To get the best signal to noise ratio with FM you need higher
deviation. If you try increase the number of FM frequencies you need
to reduce the deviation. That in turn would reduce its effectivness.
As for the original comments I would suggest there's something wrong
if AM is not clear.
Could be poor hearing, inadequate headset, turning up the volume
causing overload of either headset or receiver audio. Ignition or
alternator interference distorting the received signal, poor
transmitter, poor microphone, poor microphone technique.
Sorry but the problem is NOT AM!
Peter Dohm
>
> >"Larry Dighera" <LDig...@att.net> wrote in message
> >news:dcvif2p93dil148cv...@4ax.com...
>
> >> AM frequencies are currently 25 kHz wide. FM would require more
> >> bandwidth. Regardless, where would you place these newly allocated
> >> frequencies?
> >
>
> On Sat, 2 Sep 2006 09:10:19 -0700, "RST Engineering"
> <j...@rstengineering.com> wrote in
> <W%hKg.53$sa1.1...@news.sisna.com>:
>
> >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.
>
> That's the first time I've heard that.
>
> >The current actual transmitted bandwidth of a VHF AM signal is about 4
kHz..
>
> Does that mean the highest audio frequency transmitted it 2kHz?
>
> >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.
> >
years ago. The main reason for the relatively wide spacing was poor
frequency stability. The real problems with any changeover would/will be
the large amount of existing infrastructure in place and the need for
radically "better" adjacent channel rejection. And you don't dare to
"improve" the adjacent frequency rejection of the receivers that much untill
you are really sure that the transmitters in service can meet the new
standard ... and so forth ...
>
> And, I suspect, it would be completely impossible for FM to fit within
> 8.3 kHz channel spacing with the same fidelity?
>
just don't know of and good reason to choose one modulation scheme over the
other, and certainly not to change from one to the other!
Mxsmanic
> Wouldn't that reduce the available frequencies?
For a given audio bandwidth, FM tends to require somewhat more radio
bandwidth, as I recall, but the audio bandwidth of aviation radio is
already so limited that I don't think this would be an issue. The
gain in clarity would outweigh any loss of audio fidelity, assuming
that the same channel widths were used.
If frequencies were reallocated (instead of allocating new ones), that
would be different. That would also obsolete older equipment much
more quickly, which might not be acceptable. But there must be some
space somewhere that could be added to the frequencies, or perhaps
some band so rarely used that it could be reassigned.
Jim Logajan
> Perhaps this is a naive question, but: Why don't voice radio
> communications for aviation use FM radio instead of AM radio? 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.
If one were to mandate a replacement technology, it would be far far more
effective to use the packet-based mechanisms that digital cellular phone
technology and 802.11 wireless Ethernet (aka WiFi) rely on. Both these
technologies turn over the job of transmission collision resolution to
chip logic and take humans out of the loop. And it is possible to put
audio over WiFi using Voice over IP (VoIP) technology.
Such a system would be incredibly flexible. If one had, say, ten planes
in the air and they all started to talk to ATC at once, a packet-based
system would make it possible to do any of the following:
1) Clearly deliver only one of the voice signals to the controller and
provide a visual display that indicated 9 other planes had attempted to
speak also. It could even provide audio or visual feedback to the other 9
pilots that their transmissions were not delivered - or it could
automatically sequence the delivery of the transmissions to the
controller if the transmissions were not too lengthy.
2) If multiple controllers were available, the audio from several of the
planes could be routed to multiple controllers with no impact on audio
fidelity as far as the controllers or pilots are concerned.
3) Once you go packetized audio, you can put all sorts of useful stuff in
the packets for presentation to the other end - such as aircraft number,
the location and velocity vector from the aircraft's GPS or
altimeter/DG/airspeed indicator, and so on. A pilot could key the mike
and make a request without needing to ID themselves or their position -
that information would be extracted from the audio packet's header and
automatically presented on either a simple display to the controller or
mapped to a fancy map display.
The technical issues have been pretty much solved and commoditized in
both the WiFi VoIP and digital cellular realms. It is my humble opinion
that the radio technology currently being used for aviation
communications is now less reliable and useful than even that used in
home WiFi networks.
Maybe someday the FAA and/or ICAO will consider replacing analog radios
with a more capable digital system....
Mxsmanic
> A leading cause of accidents? Where did you get this statistic?
From the NTSB and several books on the subject.
> Guess? If a pilot or controller is not able to comprehend the other side's
> transmission, there is no guess. "Say again?" is the phrase of choice and
> it is used all over the frequencies.
It's routine in linguistics to unconsciously guess. A person
listening to familiar sounds in a familiar context will "fill in the
blanks" for any sounds that cannot be unambiguously distinguished, and
he will do this without thinking. If he guesses wrong, trouble can
result, and accidents have happened in aviation for this reason (the
most famous probably being the one at Tenerife).
Mxsmanic
> 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).
Mxsmanic
> 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.
Mxsmanic
> 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.
> Do you use an ANR headset?
No. The source of the noise is not anything around me, it's coming
from the channel itself.
> Request 'say again' if in doubt.
Most people guess without realizing it, so they cannot do that.
> 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.
RST Engineering
Jim
"Mxsmanic" <mxsm...@gmail.com> wrote in message
news:3ggjf2dda8t0c0lkq...@4ax.com...
Mxsmanic
> Really? Can you cite some statistics? I'd be very interested in
> reading them.
Just look through accident and incident reports. Radio communication
is one of the weak links in the aviation safety chain.
Stefan
> Just look through accident and incident reports. Radio communication
> is one of the weak links in the aviation safety chain.
But not because of bad sound quality, but because pilots under pressure
tend to hear what they expect to hear. (A phenomene which does not only
occur with pilots BTW.) These accidents would have happened with hifi
qualitiy radio, too.
Stefan
Mxsmanic
> You recall incorrectly.
Perhaps. Theoretically it should require exactly the same bandwidth,
but I seem to recall reading that typical implementations used more
bandwidth. In any case, you don't need much for voice communication.
The advantage of FM would be the reduction of noise. Digital over FM
would be still better.
Mxsmanic
> But not because of bad sound quality, but because pilots under pressure
> tend to hear what they expect to hear.
The worse the sound quality is, the more pilots must "fill in the
blanks," and the more likely they are to hear what they want to hear.
If you hear something that could be "five" or "nine," you're much more
likely to choose the number that suits you than you are if you hear
something that is unambiguously one of the two.
Mxsmanic
<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.
Kyle Boatright
> Emily writes:
>
>> Really? Can you cite some statistics? I'd be very interested in
>> reading them.
>
> Just look through accident and incident reports. Radio communication
> is one of the weak links in the aviation safety chain.
If you're going to make the claim, point to a viable source of information.
Without providing data, it is just your opinion.
I have read thousands of NTSB reports and don't remember a single one where
the technological limitation inherent in AM radio was a significant cause of
the accident.
> --
> Transpose mxsmanic and gmail to reach me by e-mail.
KB
Stefan
> If you hear something that could be "five" or "nine," you're much more
> likely to choose the number that suits you than you are if you hear
> something that is unambiguously one of the two.
That's exactly the reason why it's "niner".
Stefan
Peter R.
> The worse the sound quality is, the more pilots must "fill in the
> blanks," and the more likely they are to hear what they want to hear.
>
> If you hear something that could be "five" or "nine," you're much more
> likely to choose the number that suits you than you are if you hear
> something that is unambiguously one of the two.
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.
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.
--
Peter
Peter R.
> From the NTSB and several books on the subject.
Have a name of one of these books that claims that aviation communication
is the leading cause of aviation accidents?
> It's routine in linguistics to unconsciously guess. A person
> listening to familiar sounds in a familiar context will "fill in the
> blanks" for any sounds that cannot be unambiguously distinguished, and
> he will do this without thinking.
You imply that this is a very common occurrence. Sorry, but I am unable to
accept your premise without some evidence to back up this claim.
> If he guesses wrong, trouble can
> result, and accidents have happened in aviation for this reason (the
> most famous probably being the one at Tenerife).
My understanding of the accident at Tenerife is that it had more to do with
a fateful heterodyne and a captain who was asserting his own way, rather
than misunderstood communications.
--
Peter
Vaughn Simon
> 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
Mxsmanic
> My understanding of the accident at Tenerife is that it had more to do with
> a fateful heterodyne and a captain who was asserting his own way, rather
> than misunderstood communications.
Some of the words on the cockpit recording are impossible to
understand even today. That's pretty strong evidence that
misunderstood communications had an important role in this accident.
In fact, there are several instances of misunderstood radio
communication involved.
Mxsmanic
> That's exactly the reason why it's "niner".
They still sound the same if the channel is noisy enough.
Mxsmanic
> 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.
Thomas Borchert
> From the NTSB and several books on the subject.
>
Like which?
--
Thomas Borchert (EDDH)
Thomas Borchert
> > Do you use an ANR headset?
>
> No. The source of the noise is not anything around me, it's coming
> from the channel itself.
>
ANR headsets enhance speech as well as reducing noise.
--
Thomas Borchert (EDDH)
Steve Foley
> 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?
Larry Dighera
<ronca...@nospamearthlink.net> wrote in
<EKiKg.1987$v%4.1...@newsread1.news.pas.earthlink.net>:
>
>"Ron Natalie" <r...@spamcop.net> wrote in message
>news:44f9b61d$0$24183$9a6e...@news.newshosting.com...
>>
>> 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.*
Jim Logajan
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.
Jim Logajan
> 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.
Larry Dighera
wrote in <b2hjf2dvf62r2ceml...@4ax.com>:
>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.
Larry Dighera
wrote in <2eo707bxsyy7$.d...@ID-259643.user.individual.net>:
>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."
Larry Dighera
wrote in <Xns98328F9BD996...@216.168.3.30>:
>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.
Jim Logajan
> 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.)
Mxsmanic
> 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.
Mxsmanic
> 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.
Jim Logajan
> 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/2003/q3/nr_030707j.html
Dan Luke
"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.
Bollocks. One has two syllables, the other only one.
You haven't spent much time communicating via aircraft radios, have you?
--
Dan
C172RG at BFM
Jim Logajan
> 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.
Dan Luke
"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!
Stefan
> 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
NOS...@easily.co.uk
<Dwight...@dundermifflin.com> wrote:
>On Sat, 02 Sep 2006 18:03:31 +0100, NOS...@easily.co.uk 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
Jim Logajan
> 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?
;-)
Jim Logajan
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?
Vaughn Simon
"Jim Logajan" <Jam...@Lugoj.com> wrote in message
news:Xns983291682644...@216.168.3.30...
> "Vaughn Simon" <vaughnsimo...@att.FAKE.net> 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
Bob Noel
Jim Logajan <Jam...@Lugoj.com> 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
Matt Barrow
"Bob Noel" <ihates...@netscape.com.invalid> wrote in message
news:ihatessppaamm-B64...@news.isp.giganews.com...
> In article <Xns983297421D5...@216.168.3.30>,
> Jim Logajan <Jam...@Lugoj.com> 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
"Sir? If the VP is such a VIP, then shouldn't we keep the PC on the QT?
Because if word leaks to the VC he could end up MIA and we'll all be put on
KP."
Emily
> Peter R. writes:
>
>> A leading cause of accidents? Where did you get this statistic?
>
> From the NTSB and several books on the subject.
Could you provide a source? I've never heard this and I know several
NTSB employees.
Emily
> Emily writes:
>
>> Really? Can you cite some statistics? I'd be very interested in
>> reading them.
>
> Just look through accident and incident reports. Radio communication
> is one of the weak links in the aviation safety chain.
>
Has it ever been listed as a probable cause by the NTSB?
Emily
> Peter R. writes:
>
>> A leading cause of accidents? Where did you get this statistic?
>
> From the NTSB and several books on the subject.
>
>> transmission, there is no guess. "Say again?" is the phrase of choice and
>> it is used all over the frequencies.
>
> It's routine in linguistics to unconsciously guess. A person
> listening to familiar sounds in a familiar context will "fill in the
> blanks" for any sounds that cannot be unambiguously distinguished, and
> he will do this without thinking. If he guesses wrong, trouble can
> result, and accidents have happened in aviation for this reason (the
> most famous probably being the one at Tenerife).
>
Actually, in the Tenerife accident, the only radio problem was caused by
simultaneous radio transmissions by aircraft, NOT a pilot hearing want
he wanted to hear. The tower told the KLM aircraft to stand by at the
same time the Pan Am aircraft transmitted, which resulted in a blocking
of both transmissions. There were many other steps in the accident
chain, but Tenerife was most certainly not caused by a pilot hearing
what he wanted to hear.
Emily
> Peter R. writes:
>
>> a fateful heterodyne and a captain who was asserting his own way, rather
>> than misunderstood communications.
>
> Some of the words on the cockpit recording are impossible to
> misunderstood communications had an important role in this accident.
> In fact, there are several instances of misunderstood radio
> communication involved.
>
They were misunderstood a) because people were stepping on other people
and b) because the KLM crew had heavy Dutch accents. Please do a little
research before you assert such ridiculous accusations.
Emily
> Peter R. writes:
>
>> pronunciation of nine and "fife" is the proper pronunciation of five,
>
> They still sound very much the same.
>
Dave Stadt
"Emily" <rache...@yahoo.com> wrote in message
news:saednRPkopknrmfZ...@comcast.com...
Correct, and FM would not have solved any of the problems. At least with AM
the heterodyne lets people know there were multiple simultaneous
transmissions. The capture characteristics of FM do away with this
sometimes useful feature.
Dave Stadt
"Steven P. McNicoll" <ronca...@nospamearthlink.net> wrote in message
news:EKiKg.1987$v%4.1...@newsread1.news.pas.earthlink.net...
>
> "Ron Natalie" <r...@spamcop.net> wrote in message
> news:44f9b61d$0$24183$9a6e...@news.newshosting.com...
>>
>> 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, it was quite a ways down the line. Morse code via spark gap
transmitters was one of the first.
Dave Stadt
"Mxsmanic" <mxsm...@gmail.com> wrote in message
news:t4vjf2pj8ersh77lk...@4ax.com...
> 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.
Why screw around with FM. It is old technology, not much beter than AM,
and there are much better technologies that would cure the communication
problems and lack of frequency availibility.
Emily
I think it's very useful. As annoying as it is to have someone out
there with a stuck mic, what would happen if messages were stepped on
and we didn't know it?
Dave Stadt
> Emily writes:
>
>> Really? Can you cite some statistics? I'd be very interested in
>> reading them.
>
> Just look through accident and incident reports. Radio communication
> is one of the weak links in the aviation safety chain.
>
> Transpose mxsmanic and gmail to reach me by e-mail.
I read NTSB reports every day for years. I cannot remember communications
being anything more than down in the noise level as far as an accident cause
and it certainly is not a leading cause of accidents.
Dave Stadt
I have read thousands of NTSB reports and cannot remember one. Could be a
little CRS in there but not much.
James Robinson
> The tower told the KLM aircraft to stand by at the same time the Pan
> Am aircraft transmitted, which resulted in a blocking of both
> transmissions. There were many other steps in the accident chain, but
> Tenerife was most certainly not caused by a pilot hearing what he
> wanted to hear.
Then why did the aircraft start its takeoff roll, if the pilot didn't hear
what he wanted to? The tower only issued the ATC clearance, and the KLM
captain seems to have taken that as permission to take off. What else is
that but hearing what he wanted to?
Thomas Borchert
> 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.
>
Sorry, but that's just plain BS.
--
Thomas Borchert (EDDH)
Mxsmanic
> They were misunderstood a) because people were stepping on other people
> and b) because the KLM crew had heavy Dutch accents.
The reasons why they were misunderstood have never been ascertained,
and there are several possibilities. It's not even clear how much was
understood or misunderstood, since a number of the people involved are
dead. The common point to all the possible scenarios is misunderstood
radio communication.
Mxsmanic
> Actually, in the Tenerife accident, the only radio problem was caused by
> simultaneous radio transmissions by aircraft, NOT a pilot hearing want
> he wanted to hear.
There were several problems. The Pan Am crew was not sure of which
exit to take from the runway. Neither was the KLM, IIRC. The KLM
didn't understand the ATC clearance, and the tower didn't understand
the KLM acknowledgement. Pam Am said it was on the runway several
times but this was misunderstood as well. There were many
misunderstandings, most of them related to radio communication.
> The tower told the KLM aircraft to stand by at the
> same time the Pan Am aircraft transmitted, which resulted in a blocking
> of both transmissions.
Not entirely true. Part of it was audible.
> There were many other steps in the accident
> chain, but Tenerife was most certainly not caused by a pilot hearing
> what he wanted to hear.
That has never been determined. The most likely cause is that a pilot
heard what he wanted to hear, or he deliberately and negligently
ignored instructions. Other pilots may also have heard what they
wanted to hear.
Mxsmanic
> Nope, it was quite a ways down the line. Morse code via spark gap
> transmitters was one of the first.
All early audio used AM.
Mxsmanic
> Yeah. One pilot talks on AM and the other listens to FM. Great idea.
> Adds a lot of clarity to the communication.
It adds more than you would have with both pilots using AM.
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.
Mxsmanic
> Why screw around with FM. It is old technology, not much beter than AM,
> and there are much better technologies that would cure the communication
> problems and lack of frequency availibility.
Such as?
Mxsmanic
> Sorry, but that's just plain BS.
Famous last words.
Mxsmanic
> I would guess that noise-blanker and noise-limiting circuits are
> incorporated in the current radio designs.
You can't actively remove noise over a radio channel because you have
no unique identifier of noise vs. information. Noise-reduction
headsets work because they know what is noise (outside sound) and what
isn't (audio being played through the headset).
> 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.
Anything that isn't signal is noise. AM transmissions are fuzzy and
hard to hear. In fact, aviation AM radio is probably the noisiest
type of radio voice communication still in use. Most other types of
radio communication today are FM.
> What is the nature of the noise you are hearing? Can you describe it?
> Is it a hum, pulses, growling, squealing, what?
White noise. It doesn't come from anything within the aircraft or
station.
> Regardless of when it occurs, there will ultimately be an additional
> cost.
Sure, but one that companies and individuals can assume on a phased
basis at their convenience.
The fact that transponders and VORs exist today (when they did not in
the early days of aviation) proves that this works.
> 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.
Presumably they would use different 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.
Aviation is a pretty critical use of bandwidth.
> 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.
How much of aviation was designed by "professionals"?
Mxsmanic
> Bollocks. One has two syllables, the other only one.
There's a lot more to human speech than syllables. Only a single
phoneme separates the two in many pronunciations (particularly because
restricted bandwidth can limit the intelligibility of fricative
consonants), and that phoneme sounds very much like an unstressed
central hesitation vowel, which means it may not be heard at all.
This is especially true for non-rhotic speakers.
> You haven't spent much time communicating via aircraft radios, have you?
How much time have you spent studying phonetics and linguistics? They
are just as relevant here as experience with aircraft radios.
However, I don't think a wealth or dearth of experience in any domain
need be a prerequisite to discussion. And I think it more productive
to discuss the topic at hand than to direct personal attacks at anyone
with whom one disagrees.
Mxsmanic
> ...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.
The second instance involves additional or different information being
transmitted over one channel, but not the other. The first instance
involves only a reduction of noise; the information content is the
same in both channels.
> 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.
I don't know if it's better than any other transition; I just think
that something should be done to improve the archaic system that
exists now.
Stefan
> 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.
You haven't ever actually flown a plane, have you?
Stefan
Stefan
> There were many other steps in the accident
> chain, but Tenerife was most certainly not caused by a pilot hearing
> what he wanted to hear.
Actually, the KLM captain hearing what he wanted to hear was most
certainly the main cause for that accident.
As a consequence of this misunderstanding, the word "take-off" shall now
only be used in "cleared for take off" and in the read-back of this
clearance, or, at uncontrolled airfields, when a pilot says that he is
taking off. No more "ready for take off", "stand by for take off" and
the like, and no taking off before you are absolutely positively sure
that you have heard and read back the word.
But all this had nothing to do with the readability of the radio
transmissions.
Stefan
Greg Copeland
> 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.
New systems (P25) already do this type of thing. I develop digital radio
systems. Police, fire, FBI, CIA, DoD, DoE, various municipal
utilities, and various branches of the military are all taking advantage
of this technology. In many cases, the old analog systems must co-exist
with the newer P25 systems. In some cases, more rural analog systems
actually connect with a P25 network via a specialized repeated.
Integration is not a problem.
Last I read, an FAA study indicated they need lots and lots of money
(sorry, don't remember the amount) to upgrade their infrastructure from
analog to digital. The sad thing is, it does not appear Congress is going
to give it to them. Worse, the same report indicates, over the next
10-years, the FAA will exceed their required conversion dollars by simply
maintaining and repair their existing, archaic, analog infrastructure. In
other words, the FAA needs to do something...even if they are simply
updating their existing analog infrastructure. Regardless, the money does
not appear to be available.
Advantages of this technology include:
o call queuing - meaning, PTT places you in a queue so you can get a word
in, even when the controllers are very busy. BTW, this also means no more
"walked on" transmissions.
o call prioritization - All sorts of cool things can be done here -
including, most recent exchange receives priority. Also, should IFR
traffic receive higher priority over that of VFR? What about commercial
traffic? Priority could be adjusted dynamically too. This means
planes in distress could be assigned higher priority. So on and so on...
o hang timer detection - a stuck PTT is not going to lock everyone out
o caller id - imagine your tail number, altimeter, heading, and aircraft
type provided to the controller on every PTT.
o MUCHO better frequency utilization
o Limited data services
The list could go on and on...needless to say, digital has some neat
features.
The only con of digitial compared to analog is reception. With analog,
you can hear a weak signal. It may sound like absoluete crap, but you can
still hear it. With digitial, either you have a strong enough signal to
hear it...and it sounds awesome...or you hear absoluetely nothing at all.
Greg
Dan Luke
"Mxsmanic" wrote:
>> Bollocks. One has two syllables, the other only one.
>
> There's a lot more to human speech than syllables. Only a single
> phoneme separates the two in many pronunciations (particularly because
> restricted bandwidth can limit the intelligibility of fricative
> consonants), and that phoneme sounds very much like an unstressed
> central hesitation vowel, which means it may not be heard at all.
> This is especially true for non-rhotic speakers.
That is why we say "niner." In practice, it works very well to distinguish
nine from five..
>> You haven't spent much time communicating via aircraft radios, have you?
>
> How much time have you spent studying phonetics and linguistics? They
> are just as relevant here as experience with aircraft radios.
One semester in college. My guess is that's a lot longer than you've spent
talking to ATC.
> However, I don't think a wealth or dearth of experience in any domain
> need be a prerequisite to discussion. And I think it more productive
> to discuss the topic at hand than to direct personal attacks at anyone
> with whom one disagrees.
When it becomes apparent that an argument is born of ignorance, it is
appropriate to point that out. That is not a personal attack. I did not
impugn your character, merely noted the obvious: WRT aircraft radio
communications, you do not know what you are talking about.
You began this thread with the unfounded assertion that "improper and
misunderstood radio communication is a leading cause of accidents." When
Emily challenged you for evidence, you used the old, lame usenet dodge of
telling her to look it up herself. Since then, you have attempted to create
an argument based on phonetics to support a faulty premise. Your five vs.
niner attempt is the weakest yet, and you would not even have tried it if
you had any experience on the radio.
--
Dan
C172RG at BFM
Dan Luke
"Mxsmanic" wrote:
>
>> I would guess that noise-blanker and noise-limiting circuits are
>> incorporated in the current radio designs.
>
> You can't actively remove noise over a radio channel because you have
> no unique identifier of noise vs. information.
Bollocks again. I have a radio that does actively remove noise--it has a
button to turn the feature on and off, and it works quite well.
I'll say one thing for you, you are fearless in your ignorance.
Mxsmanic
> New systems (P25) already do this type of thing. I develop digital radio
> systems. Police, fire, FBI, CIA, DoD, DoE, various municipal
> utilities, and various branches of the military are all taking advantage
> of this technology. In many cases, the old analog systems must co-exist
> with the newer P25 systems. In some cases, more rural analog systems
> actually connect with a P25 network via a specialized repeated.
> Integration is not a problem.
So why wouldn't it extend to aviation?
> Last I read, an FAA study indicated they need lots and lots of money
> (sorry, don't remember the amount) to upgrade their infrastructure from
> analog to digital.
They need not upgrade it all at once.
> The sad thing is, it does not appear Congress is going
> to give it to them.
Congress, like most of America, is hysterical about imaginary human
threats these days, and has probably lost track of the much more
mundane but much more serious safety risks associated with
infrastructure, aircraft, and crews.
> Advantages of this technology include:
> o call queuing - meaning, PTT places you in a queue so you can get a word
> in, even when the controllers are very busy. BTW, this also means no more
> "walked on" transmissions.
Do other aircraft hear the transmission when you make it, or when the
controller hears it? Granted, they are only supposed to listen to the
controller, but in practice they will be listening to other aircraft
as well.
How do you make this work in parallel with analog systems that cannot
queue?
> o call prioritization - All sorts of cool things can be done here -
> including, most recent exchange receives priority. Also, should IFR
> traffic receive higher priority over that of VFR? What about commercial
> traffic? Priority could be adjusted dynamically too. This means
> planes in distress could be assigned higher priority. So on and so on...
It's best not to jump off the deep end with gadgets. Just because
something can be done doesn't mean that it should be done.
> o caller id - imagine your tail number, altimeter, heading, and aircraft
> type provided to the controller on every PTT.
Where does this leave people with analog equipment?
> o Limited data services
What kind of data services do pilots need? Are they going to be
surfing the Web?
> The list could go on and on...needless to say, digital has some neat
> features.
Neat features aren't necessarily desirable features. There is too
much of a tendency to bloat digital systems with features that have
been hastily designed, inadequately analyzed, and barely tested at
all.
> The only con of digitial compared to analog is reception. With analog,
> you can hear a weak signal. It may sound like absoluete crap, but you can
> still hear it. With digitial, either you have a strong enough signal to
> hear it...and it sounds awesome...or you hear absoluetely nothing at all.
If the digital threshold is set where the threshold of intelligibility
would be in analog, there's no net loss.
Dan Luke
"Thomas Borchert" wrote:
He's got a ton of it to spread around.
Mxsmanic
> Bollocks again. I have a radio that does actively remove noise--it has a
> button to turn the feature on and off, and it works quite well.
What kind of noise does it remove, and how does it distinguish noise
from signal?
Vaughn Simon
> Dave Stadt writes:
>
>> Why screw around with FM. It is old technology, not much beter than AM,
>> and there are much better technologies that would cure the communication
>> problems and lack of frequency availibility.
>
> Such as?
Such as VOIP actually, or other digital technologies that are now quite
common, cheap, and "off the shelf". In police and fire communications, FM is
quickly giving away to digital modes. My bad for previously talking about FM as
if it were the only possibility.
A digital-capable radio does not care if it is transmitting voice or data, so it
could someday allow truly automated flight control. For example, you might be
able to get clearance into controlled airspace automatically and have it show up
as a green dotted line on your MFD, to be acknowledged with the mere push of a
button.
Larry Dighera
wrote in <1bflf298qlf4rjqg0...@4ax.com>:
>
>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.
You'll have to cite a source for this nugget of knowledge. Are you
familiar with Common Traffic Advisory Frequency (CTAF)?
Mxsmanic
> Such as VOIP actually, or other digital technologies that are now quite
> common, cheap, and "off the shelf". In police and fire communications, FM is
> quickly giving away to digital modes.
I doubt that they are using VoIP, though, which is notoriously
unreliable.
I'm not sure that cheap, common or "off-the-shelf" should be the top
criteria for choosing a replacement for AM radio. I think "safe"
should be the highest priority. If it improves safety, it's good; if
it doesn't, it's bad (unless it can improve something else _without_
compromising safety).
> A digital-capable radio does not care if it is transmitting voice or data, so it
> could someday allow truly automated flight control. For example, you might be
> able to get clearance into controlled airspace automatically and have it show up
> as a green dotted line on your MFD, to be acknowledged with the mere push of a
> button.
But then you won't need pilots. Actually, it is nearly possible to do
without them today--but radio communication is still one of the
sticking points.
Mxsmanic
> You'll have to cite a source for this nugget of knowledge.
FAA AIMs and CFRs make it pretty clear that communications involving a
controller are pilot-controller exchanges, not pilot-pilot exchanges.
> Are you familiar with Common Traffic Advisory Frequency (CTAF)?
Yes, but it and similar schemes don't involve a controller, so
obviously the communication is between aircraft directly.
Dan Luke
"Mxsmanic" wrote:
> Dan Luke writes:
>
>> Bollocks again. I have a radio that does actively remove noise--it has a
>> button to turn the feature on and off, and it works quite well.
>
> What kind of noise does it remove, and how does it distinguish noise
> from signal?
It removes a lot of the static noise. I do not know the technical details
of how it does it. However, the freqencies of human speech do not cover the
audible spectrum, and all extraneous frequencies may be filtered quite
easily. Even frequencies at the upper and lower ends of human speech may be
filtered with minimal effect on intelligibility. Perhaps it's as simple as
that.
Dan Luke
"Mxsmanic" wrote:
>
> However, you're not supposed to listen to other pilots; you're
> supposed to listen to controllers.
Utter nonsense.
It will be entertaining to see what bs you come up with next.
Vaughn Simon
> Vaughn Simon writes:
>
>> Such as VOIP actually, or other digital technologies that are now quite
>> common, cheap, and "off the shelf". In police and fire communications, FM is
>> quickly giving away to digital modes.
>
> I doubt that they are using VoIP, though, which is notoriously
> unreliable.
You should a bit of reading before you make such comments. I happen to be in
the public safety communications field, and we are right now phasing out our old
trunked FM system for a VOIP system. We have already scrapped our old phone
systems in favor of VOIP and that is working just fine. If VOIP were
"notoriously unreliable" we would hardly use it for public safety
communications.
Vaughn
Mxsmanic
> You should a bit of reading before you make such comments. I happen to be in
> the public safety communications field, and we are right now phasing out our old
> trunked FM system for a VOIP system. We have already scrapped our old phone
> systems in favor of VOIP and that is working just fine. If VOIP were
> "notoriously unreliable" we would hardly use it for public safety
> communications.
Wait and see.