"Jerry Avins" <jya@ieee.org> wrote in message news:QPydnTVCEMBYq9nYnZ2dnUVZ_qOdnZ2d@rcn.net...> John Monro wrote: >> Jerry Avins wrote: >> snip >> Moral: matching load to source is a good way to avoid >>> reflections. Matching source to load is a poor way to >>> deliver power. >>> >>> Jerry >> >> Matching source to load is good when you are not paying >> for the power dissipated in the source. For example, >> when the source is a receiving antenna or a solar cell. > > As for power delivered, when you can use a transformer to > effect the match, it is worth while. On the other hand, > I've seen designs with series resistors supposedly to > effect a match, and that's nuts.Nuts from the point of view of maximizing power transfer. Not necessarily nuts from the point of view of eliminating resonances and reflections in the transmission line.
How can digital be more spectrum efficient than analog ?
Started by ●October 27, 2006
Reply by ●October 29, 20062006-10-29
Reply by ●October 29, 20062006-10-29
John E. Hadstate wrote:> "Jerry Avins" <jya@ieee.org> wrote in message > news:QPydnTVCEMBYq9nYnZ2dnUVZ_qOdnZ2d@rcn.net... >> John Monro wrote: >>> Jerry Avins wrote: >>> snip >>> Moral: matching load to source is a good way to avoid >>>> reflections. Matching source to load is a poor way to >>>> deliver power. >>>> >>>> Jerry >>> Matching source to load is good when you are not paying >>> for the power dissipated in the source. For example, >>> when the source is a receiving antenna or a solar cell. >> As for power delivered, when you can use a transformer to >> effect the match, it is worth while. On the other hand, >> I've seen designs with series resistors supposedly to >> effect a match, and that's nuts. > > Nuts from the point of view of maximizing power transfer. > Not necessarily nuts from the point of view of eliminating > resonances and reflections in the transmission line.Agreed (and mentioned in passing at some point). But I don't think that Randy had reflection in mind when he asked the question I responded to. Jerry -- "The rights of the best of men are secured only as the rights of the vilest and most abhorrent are protected." - Chief Justice Charles Evans Hughes, 1927 ���������������������������������������������������������������������
Reply by ●October 29, 20062006-10-29
Floyd L. Davidson wrote:> Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> wrote:...>>> Above a minimum SNR digital systems are essentially error free >>> while analog system have additive noise. >> Unfortunately bandwidth is never unlimited & the noise level can >> occaisionally be out of your control. > > A useless statement of no significance.I think you simply missed the significance.>> Digital systems are far less >> tolerent of noise when it *does* exceed the critical level. Analog >> systems get "hissy", digitas ge& ..or_de^5T3+... > > Wrong. A digital system can function error free at an SNR so > low that analog systems cannot function at all, much less simply > get hissy.A digital system useful where SNR is very low has a very low threshold and very low throughput. A system intended for a clean channel behaves as H.E. described it. You guys seem to be describing different parts of the elephant. ... Jerry -- "The rights of the best of men are secured only as the rights of the vilest and most abhorrent are protected." - Chief Justice Charles Evans Hughes, 1927 ���������������������������������������������������������������������
Reply by ●October 29, 20062006-10-29
"Floyd L. Davidson" <floyd@apaflo.com> wrote in message news:87wt6j8ol5.fld@apaflo.com...> Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> > wrote: >> >>Digital systems are far less >>tolerent of noise when it *does* exceed the critical >>level. Analog >>systems get "hissy", digitas ge& ..or_de^5T3+... > > Wrong. A digital system can function error free at an SNR > so > low that analog systems cannot function at all, much less > simply > get hissy. >Non-sequitur, but what you really meant to say is also wrong! You just stepped-on Shannon yourself. Where the rubber meets the road, there is no "digital system." Everything is analog. (In a digital environment there is no noise, so SNR is a useless concept.) While Shannon measures information in "bits", he is not talking about communicating in a digital environment. Analog channels pass information bits subject to the SNR vs. Bandwidth trade-off formally expressed by Shannon. Indeed, "a digital system can function error-free at an SNR so low that analog systems cannot function at all..." but that is entirely irrelevant. To achieve this magical feat, it must do so at a reduced *information* rate (forward-error-correction bits, retransmissions, etc. don't count as information).
Reply by ●October 29, 20062006-10-29
"Floyd L. Davidson" <floyd@apaflo.com> wrote in message news:87wt6j8ol5.fld@apaflo.com...> Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> > wrote: >> >>Digital systems are far less >>tolerent of noise when it *does* exceed the critical >>level. Analog >>systems get "hissy", digitas ge& ..or_de^5T3+... > > Wrong. A digital system can function error free at an SNR > so > low that analog systems cannot function at all, much less > simply > get hissy. >Non-sequitur, but what you really meant to say is also wrong! You just stepped-on Shannon yourself. Where the rubber meets the road, there is no "digital system." Everything is analog. (In a digital environment there is no noise, so SNR is a useless concept.) While Shannon measures information in "bits", he is not talking about communicating in a digital environment. Analog channels pass information bits subject to the SNR vs. Bandwidth trade-off formally expressed by Shannon. Indeed, "a digital system can function error-free at an SNR so low that analog systems cannot function at all..." but that is entirely irrelevant. To achieve this magical feat, it must do so at a reduced *information* rate (forward-error-correction bits, retransmissions, etc. don't count as information).
Reply by ●October 29, 20062006-10-29
"Floyd L. Davidson" <floyd@apaflo.com> wrote in message news:87wt6j8ol5.fld@apaflo.com...> Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> > wrote: >> >>Digital systems are far less >>tolerent of noise when it *does* exceed the critical >>level. Analog >>systems get "hissy", digitas ge& ..or_de^5T3+... > > Wrong. A digital system can function error free at an SNR > so > low that analog systems cannot function at all, much less > simply > get hissy. >Non-sequitur, but what you really meant to say is also wrong! You just stepped-on Shannon yourself. Where the rubber meets the road, there is no "digital system." Everything is analog. (In a digital environment there is no noise, so SNR is a useless concept.) While Shannon measures information in "bits", he is not talking about communicating in a digital environment. Analog channels pass information bits subject to the SNR vs. Bandwidth trade-off formally expressed by Shannon. Indeed, "a digital system can function error-free at an SNR so low that analog systems cannot function at all..." but that is entirely irrelevant. To achieve this magical feat, it must do so at a reduced *information* rate (forward-error-correction bits, retransmissions, etc. don't count as information).
Reply by ●October 29, 20062006-10-29
Jerry Avins <jya@ieee.org> wrote:>Floyd L. Davidson wrote: >> Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> wrote: > > ... > >>>> Above a minimum SNR digital systems are essentially error free >>>> while analog system have additive noise. >>> Unfortunately bandwidth is never unlimited & the noise level can >>> occaisionally be out of your control. >> A useless statement of no significance. > >I think you simply missed the significance.It is a non sequitur, with no significance to the statement it references. Nobody has suggested there is such a thing as unlimited bandwidth, ever. That was not part of the discussion, and adds nothing to our understanding of why or when a digital system is better or worse than an analog system. It certainly has nothing to do with the quoted statement retained above regarding the SNR threshold characteristic of digital carrier systems vs. the additive noise of analog systems.>>> Digital systems are far less >>> tolerent of noise when it *does* exceed the critical level. Analog >>> systems get "hissy", digitas ge& ..or_de^5T3+... >> Wrong. A digital system can function error free at an SNR so >> low that analog systems cannot function at all, much less simply >> get hissy. > >A digital system useful where SNR is very low has a very low >threshold and very low throughput.Fiber optics is a well understood example of a low SNR environment where digital carrier systems provide significant advantages in an environment where analog carrier can barely function. Clearly fiber is not a system with very low throughput...>A system intended for a clean >channel behaves as H.E. described it. You guys seem to be >describing different parts of the elephant.It may be true that a system intended for a clean channel behaves as he described, but that does not negated the fact that a system which must operate under less than optimum conditions does *not* work as he described. -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Reply by ●October 29, 20062006-10-29
"Floyd L. Davidson" <floyd@apaflo.com> wrote in message news:87pscb8bhj.fld@apaflo.com...> Jerry Avins <jya@ieee.org> wrote: >>Floyd L. Davidson wrote: >>> Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> >>> wrote: >> >> ... >> >>>>> Above a minimum SNR digital systems are essentially >>>>> error free >>>>> while analog system have additive noise. >>>> Unfortunately bandwidth is never unlimited & the noise >>>> level can >>>> occaisionally be out of your control. >>> A useless statement of no significance. >> >>I think you simply missed the significance. > > It is a non sequitur, with no significance to the > statement it > references. Nobody has suggested there is such a thing as > unlimited bandwidth, ever. That was not part of the > discussion, > and adds nothing to our understanding of why or when a > digital > system is better or worse than an analog system. It > certainly > has nothing to do with the quoted statement retained above > regarding the SNR threshold characteristic of digital > carrier > systems vs. the additive noise of analog systems.You are thoroughly confusing the terms "analog" and "digital" with specific types of modulation methods. Later on in this post, you seemed to suggest that analog (in a fiber channel) must somehow be equated to baseband signalling. H.E.'s observation is not a non-sequitur. It is, in fact, central to the concept of a trade-off between noise and bandwidth. Anyone who understands Shannon also understands that you, yourself, "suggested that there is such a thing as unlimited bandwidth", when you stated that "above a minimum SNR, digital systems are essentially error free": "error-free" with non-zero noise and an information rate greater than zero implies infinite bandwidth. That is, unless you were actually talking about a digital system (where there is no noise) rather than a modulation technique, in which case, you are the one spewing non-sequiturs.
Reply by ●October 29, 20062006-10-29
"John E. Hadstate" <jh113355@hotmail.com> wrote:>"Floyd L. Davidson" <floyd@apaflo.com> wrote in message >news:87wt6j8ol5.fld@apaflo.com... >> Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> >> wrote: >>> >>>Digital systems are far less >>>tolerent of noise when it *does* exceed the critical >>>level. Analog >>>systems get "hissy", digitas ge& ..or_de^5T3+... >> >> Wrong. A digital system can function error free at an SNR >> so >> low that analog systems cannot function at all, much less >> simply >> get hissy. >> > >Non-sequitur, but what you really meant to say is also >wrong! You just stepped-on Shannon yourself. Where the >rubber meets the road, there is no "digital system." >Everything is analog. (In a digital environment there is no >noise, so SNR is a useless concept.)That paragraph is erroneous on each and every point. You obviously do not understand what defines a "digital" system. And you should read Shannon's paper...>While Shannon measures information in "bits", he is not >talking about communicating in a digital environment.The first two parts to Shannon's 1948 paper titled "A Mathematical Theory of Communications" are labeled "DISCRETE NOISELESS SYSTEMS" and "THE DISCRETE CHANNEL WITH NOISE". Those are an analysis of digital systems, first without noise and then with noise. Part 4 is titled "THE CONTINUOUS CHANNEL" and Part 5 is "THE RATE FOR A CONTINUOUS SOURCE", both of which are analysis of analog systems.>Analog channels pass information bits subject to the SNR vs. >Bandwidth trade-off formally expressed by Shannon. > >Indeed, "a digital system can function error-free at an SNR >so low that analog systems cannot function at all..." but >that is entirely irrelevant.Apparently not to the telephone industry! They have long since been taking advantage of that to make fiber optic systems ubiquitous. (I might note that it was not irrelevant to Claude Shannon in the 1940's either... the first sentence in his 1948 paper says, "The recent development of various methods of modulation such as PCM and PPM which exchange bandwidth for signal-to-noise ratio has intensified the interest in a general theory of communication.")>To achieve this magical feat, >it must do so at a reduced *information* rate >(forward-error-correction bits, retransmissions, etc. don't >count as information)."forward-error-correction bits"??? Whatever. Do you know what the SNR on a typical fiber optic cable is, and what the typical bit error rate for fiber digital systems is? -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Reply by ●October 29, 20062006-10-29
"John E. Hadstate" <jh113355@hotmail.com> wrote:>"Floyd L. Davidson" <floyd@apaflo.com> wrote in message >news:87wt6j8ol5.fld@apaflo.com... >> Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> >> wrote: >>> >>>Digital systems are far less >>>tolerent of noise when it *does* exceed the critical >>>level. Analog >>>systems get "hissy", digitas ge& ..or_de^5T3+... >> >> Wrong. A digital system can function error free at an SNR >> so >> low that analog systems cannot function at all, much less >> simply >> get hissy. >> > >Non-sequitur, but what you really meant to say is also >wrong! You just stepped-on Shannon yourself. Where the >rubber meets the road, there is no "digital system." >Everything is analog. (In a digital environment there is no >noise, so SNR is a useless concept.)That paragraph is erroneous on each and every point. You obviously do not understand what defines a "digital" system. And you should read Shannon's paper...>While Shannon measures information in "bits", he is not >talking about communicating in a digital environment.The first two parts to Shannon's 1948 paper titled "A Mathematical Theory of Communications" are labeled "DISCRETE NOISELESS SYSTEMS" and "THE DISCRETE CHANNEL WITH NOISE". Those are an analysis of digital systems, first without noise and then with noise. Part 4 is titled "THE CONTINUOUS CHANNEL" and Part 5 is "THE RATE FOR A CONTINUOUS SOURCE", both of which are analysis of analog systems.>Analog channels pass information bits subject to the SNR vs. >Bandwidth trade-off formally expressed by Shannon. > >Indeed, "a digital system can function error-free at an SNR >so low that analog systems cannot function at all..." but >that is entirely irrelevant.Apparently not to the telephone industry! They have long since been taking advantage of that to make fiber optic systems ubiquitous. (I might note that it was not irrelevant to Claude Shannon in the 1940's either... the first sentence in his 1948 paper says, "The recent development of various methods of modulation such as PCM and PPM which exchange bandwidth for signal-to-noise ratio has intensified the interest in a general theory of communication.")>To achieve this magical feat, >it must do so at a reduced *information* rate >(forward-error-correction bits, retransmissions, etc. don't >count as information)."forward-error-correction bits"??? Whatever. Do you know what the SNR on a typical fiber optic cable is, and what the typical bit error rate for fiber digital systems is? -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
