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#131
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Why don't voice radio communications use FM?
On Sun, 03 Sep 2006 13:39:09 +0200, Mxsmanic
wrote in : Larry Dighera writes: 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. I believe you'll find Mr. Weir* will take issue with your statement above. 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. Where do you get these unsupported statistics? 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. Now we're getting somewhere. So that we are all on the same page, here's a definition of White noise: http://en.wikipedia.org/wiki/White_noise [There's an audio sample here also, so you can actually hear it] White noise is a random signal (or process) with a flat power spectral density. In other words, the signal's power spectral density has equal power in any band, at any centre frequency, having a given bandwidth. White noise is considered analogous to white light which contains all frequencies. An infinite-bandwidth white noise signal is purely a theoretical construct. By having power at all frequencies, the total power of such a signal is infinite. In practice, a signal can be "white" with a flat spectrum over a defined frequency band. http://en.wikipedia.org/wiki/White_noise_machine A white noise machine is a device that produces a sound that is random in character, somewhat like air escaping from a balloon. They generally do not produce actual white noise, which has a harsh sound, but more often pink noise, whose power rolls off at higher frequencies, or other colors of noise. They are often used to protect privacy by masking distant conversations, say in a psychiatrist's waiting room, and are also sold as sleep aids. White Noise Machines produces a sound like the gentle whoosh. Since the sound is absolutely constant but has no structure, the brain simply tunes it out - just like you have tuned out the noise from the fans in your computer. You hear the fans, but how often do you actually notice them? So, there is a hiss in your receiver when you listen to aviation communications, and you find it masks intelligibility. Now that you mention it, I suppose you are correct, because when I turn the Squelch down, I hear a hiss. The volume of the hiss is much greater when there is no radio signal present, because the AGC/AVC circuits are operating at maximum amplification; when a radio signal is present, that hiss is significantly diminished in volume to the point, that in 36 years of aviation experience, I've never found it an issue. Perhaps the hiss to which you object is unique to your radio receiving equipment. How many aviation radios have you had the opportunity to listen to? Have you found the same objectionable hiss in all aviation radio receivers you've used? 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. So you are proposing that the worldwide aviation community re-equip all their aircraft and facilities with FM, and that all aviation stakeholders bear the cost of those conversion, so that you won't hear a hiss? Do you really believe that what you propose will pay dividends commensurate with its cost? The fact that transponders and VORs exist today (when they did not in the early days of aviation) proves that this works. In the case of transponders, they were not necessary to operate within the NAS. Anyone who believes that radio communication is not necessary to operate within the NAS isn't operating in Class B, C, or D airspace without prior permission, and the flight mission is not really meaningful in the sense of accomplishing a meaningful result like transportation. In the case of VORs replacing Radio Range and NDBs, those are not _two-way_ communications, so they are in a different class than aviation radio communications. Concurrent operation of differing radio based communication systems is possible, but to concurrently operate two incompatible aviation communication systems isn't practicable, because it would require _all_ air and ground systems to be equipped with both AM and FM equipment simultaneously and instantly. If not, FM transmissions would not be received by those stations not equipped with FM receivers, and vice versa. For situational awareness, it is vital for all participants to know what the others in the vicinity are doing by hearing their instructions and intentions over the radio. For example, when I'm VFR en route, and hear a military transport "cleared for the approach" to an airport across whose instrument approach path I'm about to traverse, although the transmission isn't directed to me, it provides me with safety information that may be vital to my visually acquiring conflicting air traffic. 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"? You'll find it difficult to find a pilot who regards today's NAS as armaturely designed. Are you familiar with TERPS?** * http://www.rst-engr.com/rst/about_us...%20Engineering ** http://www.faa.gov/about/office_org/...afs400/afs420/ |
#132
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Why don't voice radio communications use FM?
Mxsmanic wrote:
Emily writes: We haven't yet, in almost 100 years. Cutting-edge technology is relatively new in its current profusion, and there's always a first time. Will you bet your life on it? Since our technology is used on most aircraft I fly on, I already do. |
#133
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Why don't voice radio communications use FM?
On Sun, 03 Sep 2006 16:04:01 +0200, Mxsmanic
wrote in : Larry Dighera writes: 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. FAA AIMs and CFRs make it pretty clear that communications involving a controller are pilot-controller exchanges, not pilot-pilot exchanges. While that may be true, it in no way relates to your statement quoted above. Stating "you're not supposed to listen to other pilots" is just plain wrong. Pilots listen to other pilot transmissions to increase their situational awareness. 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. Thank you. |
#134
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Why don't voice radio communications use FM?
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#135
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Why don't voice radio communications use FM?
Mxsmanic wrote:
Dan Luke writes: ******** 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? One proven way to reduce noise is to repeat the signal N times and the receiver adds up the repetitions and eventually the noise averages to zero while the signal does not. Of course this is not what is done in practice in real communications. (I once wrote software for a Tunneling Electron Microscope (TEM) that did the above - the target object is repeatedly scanned and the scans are basically averaged - the noise falls off. Though IIRC, the amplitude of the noise drops by a factor of 1/sqrt(N) for N scans. I'm too lazy to look it up so that might not be the correct factor.) |
#136
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Why don't voice radio communications use FM?
Emily writes:
The difference is, I never said I'd read it. YOU did. A key to progress in debate is knowing what you are talking about. What you actually say about what you know is irrelevant. -- Transpose mxsmanic and gmail to reach me by e-mail. |
#137
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Why don't voice radio communications use FM?
Emily writes:
Show me the line where it says AM had anything to do with it. All of the radio communication was AM. -- Transpose mxsmanic and gmail to reach me by e-mail. |
#138
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Why don't voice radio communications use FM?
Larry Dighera writes:
I believe you'll find Mr. Weir* will take issue with your statement above. He is welcome to do so. So you are proposing that the worldwide aviation community re-equip all their aircraft and facilities with FM, and that all aviation stakeholders bear the cost of those conversion, so that you won't hear a hiss? I suggest that a less noisy method of communication be found and implemented, so as to increase safety by improving the reliability of voice radio communication. Do you really believe that what you propose will pay dividends commensurate with its cost? Yes. In the case of transponders, they were not necessary to operate within the NAS. At one time, transponders were not needed at all. Then they were. So obviously things can change. In the case of VORs replacing Radio Range and NDBs, those are not _two-way_ communications, so they are in a different class than aviation radio communications. They still require new equipment at both ends of the communications link. Concurrent operation of differing radio based communication systems is possible, but to concurrently operate two incompatible aviation communication systems isn't practicable, because it would require _all_ air and ground systems to be equipped with both AM and FM equipment simultaneously and instantly. Why? If not, FM transmissions would not be received by those stations not equipped with FM receivers, and vice versa. Since everything would be transmitted in both AM and FM by stations equipped for FM, they would always be receivable by stations equipped only for AM. For situational awareness, it is vital for all participants to know what the others in the vicinity are doing by hearing their instructions and intentions over the radio. Which is one reason why things like message queuing are potentially dangerous. For example, when I'm VFR en route, and hear a military transport "cleared for the approach" to an airport across whose instrument approach path I'm about to traverse, although the transmission isn't directed to me, it provides me with safety information that may be vital to my visually acquiring conflicting air traffic. You can do even better by flying IFR, but you can also get by with visual contact only. Every increment in technology ideally provides an increment in safety, but it's best to avoid designing systems that increment safety for those who have them but reduce safety for those who do not. You'll find it difficult to find a pilot who regards today's NAS as armaturely designed. Are you familiar with TERPS?** No. -- Transpose mxsmanic and gmail to reach me by e-mail. |
#139
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Why don't voice radio communications use FM?
Mxsmanic,
A key to progress in debate is knowing what you are talking about. What you actually say about what you know is irrelevant. You're truly a piece of work. -- Thomas Borchert (EDDH) |
#140
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Why don't voice radio communications use FM?
Mxsmanic,
All of the radio communication was AM. It was gravity's fault. All the planes were under its influence. No wait, it was the ocean's fault. All planes were surrounded by it. And so on... -- Thomas Borchert (EDDH) |
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