Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> wrote:>On Fri, 27 Oct 2006 10:29:06 -0500, no-top-post wrote: > >>It's common knowledge that digital technology gives more telephone >>[4 Khz wide] channels than analog technology - for the same spectrum >>width. This even with the steep-sided filters and SSB technology. >> >T'aint nesessarily so. As another poster pointed out FDM could >squeeze 24 channels os SSB 4kz voice into 96 KHz. where a T1 takes >over 1.5 megabits/sec to do the same thing.Comparing bandwidth to bit rate is nonsense! 96 KHz does not compare to 1.5 Mbps in any productive way. Keep in mind that a telco voice channel is 4 KHz analog, but over the same bandwidth one can easily send a 64 Kbps digital PAM signal (i.e., v.90) using the exact same codec in the telephone switch line card. Bandwidth does not use more bitrate, it provides more! Shannon showed channel capacity to be relative to both bandwidth and signal-to-noise ratio. Anything you do to change one *requires* a change in the other to maintain the same maximum capacity. Different carrier systems do exactly that, balancing between SNR and bandwidth. Bandwidth is not what makes digital more effective than analog. Above a minimum SNR digital systems are essentially error free while analog system have additive noise. For that reason digital is usually prefered. The second most significant reason is the ease with which digital carrier systems can be designed to trade SNR for bandwidth by using multi-level encoding, which means well matched adaptions to anything from very noisy fiber optics to very quiet coax cable. -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
How can digital be more spectrum efficient than analog ?
Started by ●October 27, 2006
Reply by ●October 28, 20062006-10-28
Reply by ●October 28, 20062006-10-28
Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> wrote:>On Fri, 27 Oct 2006 10:29:06 -0500, no-top-post wrote: > >>It's common knowledge that digital technology gives more telephone >>[4 Khz wide] channels than analog technology - for the same spectrum >>width. This even with the steep-sided filters and SSB technology. >> >T'aint nesessarily so. As another poster pointed out FDM could >squeeze 24 channels os SSB 4kz voice into 96 KHz. where a T1 takes >over 1.5 megabits/sec to do the same thing.Comparing bandwidth to bit rate is nonsense! 96 KHz does not compare to 1.5 Mbps in any productive way. Keep in mind that a telco voice channel is 4 KHz analog, but over the same bandwidth one can easily send a 64 Kbps digital PAM signal (i.e., v.90) using the exact same codec in the telephone switch line card. Bandwidth does not use more bitrate, it provides more! Shannon showed channel capacity to be relative to both bandwidth and signal-to-noise ratio. Anything you do to change one *requires* a change in the other to maintain the same maximum capacity. Different carrier systems do exactly that, balancing between SNR and bandwidth. Bandwidth is not what makes digital more effective than analog. Above a minimum SNR digital systems are essentially error free while analog system have additive noise. For that reason digital is usually prefered. The second most significant reason is the ease with which digital carrier systems can be designed to trade SNR for bandwidth by using multi-level encoding, which means well matched adaptions to anything from very noisy fiber optics to very quiet coax cable. -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Reply by ●October 28, 20062006-10-28
Howard Eisenhauer <howarde@REMOVECAPShfx.eastlink.ca> wrote:>On Fri, 27 Oct 2006 10:29:06 -0500, no-top-post wrote: > >>It's common knowledge that digital technology gives more telephone >>[4 Khz wide] channels than analog technology - for the same spectrum >>width. This even with the steep-sided filters and SSB technology. >> >T'aint nesessarily so. As another poster pointed out FDM could >squeeze 24 channels os SSB 4kz voice into 96 KHz. where a T1 takes >over 1.5 megabits/sec to do the same thing.Comparing bandwidth to bit rate is nonsense! 96 KHz does not compare to 1.5 Mbps in any productive way. Keep in mind that a telco voice channel is 4 KHz analog, but over the same bandwidth one can easily send a 64 Kbps digital PAM signal (i.e., v.90) using the exact same codec in the telephone switch line card. Bandwidth does not use more bitrate, it provides more! Shannon showed channel capacity to be relative to both bandwidth and signal-to-noise ratio. Anything you do to change one *requires* a change in the other to maintain the same maximum capacity. Different carrier systems do exactly that, balancing between SNR and bandwidth. Bandwidth is not what makes digital more effective than analog. Above a minimum SNR digital systems are essentially error free while analog system have additive noise. For that reason digital is usually prefered. The second most significant reason is the ease with which digital carrier systems can be designed to trade SNR for bandwidth by using multi-level encoding, which means well matched adaptions to anything from very noisy fiber optics to very quiet coax cable. -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Reply by ●October 28, 20062006-10-28
Don Bowey <dbowey@comcast.net> wrote:>On 10/27/06 8:36 PM, in article kmg5k21ljhik3sgfecg6br34u2llkko0cn@4ax.com, >"Howard Eisenhauer" <howarde@REMOVECAPShfx.eastlink.ca> wrote: >> Telcos sometimes cut the 64 Kbit/VC rate down to 32 Kbits for a 2-1 >> improvent in transmission capacity, This doesn't really sound any >> worse for voice but don't try to send high speed data over it :(. > >Name even one real telco that does that. I can't think of one. ADPCM is >used, however, in many private networks.It is quite common any where that bandwidth is at a premium. Satellite circuits are the most obvious, but there are others. -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Reply by ●October 28, 20062006-10-28
floyd@apaflo.com (Floyd L. Davidson) writes:> [...] > digital is usually prefered. The second most significant reason > is the ease with which digital carrier systems can be designed > to trade SNR for bandwidth by using multi-level encoding, which > means well matched adaptions to anything from very noisy fiber > optics to very quiet coax cable.Hmm. Your statement reminds me of getting full-power transfer by matching impedances. Could information transfer be viewed similarly, i.e., by matching the "impedance" of the transmitter to the "impedance" of the channel? -- % Randy Yates % "Remember the good old 1980's, when %% Fuquay-Varina, NC % things were so uncomplicated?" %%% 919-577-9882 % 'Ticket To The Moon' %%%% <yates@ieee.org> % *Time*, Electric Light Orchestra http://home.earthlink.net/~yatescr
Reply by ●October 28, 20062006-10-28
Randy Yates wrote:> floyd@apaflo.com (Floyd L. Davidson) writes: >> [...] >> digital is usually prefered. The second most significant reason >> is the ease with which digital carrier systems can be designed >> to trade SNR for bandwidth by using multi-level encoding, which >> means well matched adaptions to anything from very noisy fiber >> optics to very quiet coax cable. > > Hmm. Your statement reminds me of getting full-power transfer by > matching impedances. Could information transfer be viewed similarly, > i.e., by matching the "impedance" of the transmitter to the > "impedance" of the channel?I doubt it. You get as much power as you can when you match the load to the source, but you get it at 50% efficiency. Consider a 12V battery with a .01-ohm internal resistance. With There is 6 volts across a matched load, and the total power power is 7.2 KW divided equally between the load and the battery. (For a short while, anyway.) Moral: matching load to source is a good way to avoid reflections. Matching source to load is a poor way to deliver power. 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 28, 20062006-10-28
Jerry Avins <jya@ieee.org> wrote:>Randy Yates wrote: >> floyd@apaflo.com (Floyd L. Davidson) writes: >>> [...] >>> digital is usually prefered. The second most significant reason >>> is the ease with which digital carrier systems can be designed >>> to trade SNR for bandwidth by using multi-level encoding, which >>> means well matched adaptions to anything from very noisy fiber >>> optics to very quiet coax cable. >> Hmm. Your statement reminds me of getting full-power transfer >> by >> matching impedances. Could information transfer be viewed similarly, >> i.e., by matching the "impedance" of the transmitter to the >> "impedance" of the channel?Yes. That is an interesting comparison.>I doubt it. You get as much power as you can when you match the >load to the source, but you get it at 50% efficiency. > >Consider a 12V battery with a .01-ohm internal resistance. With >There is 6 volts across a matched load, and the total power >power is 7.2 KW divided equally between the load and the >battery. (For a short while, anyway.) Moral: matching load to >source is a good way to avoid reflections. Matching source to >load is a poor way to deliver power.That is *not* an impedance match. It discusses DC resistance, not impedances. It is not a valid desciption of what happens with matched vs. unmatched imedpances, and does not compare well with what was being discussed. -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Reply by ●October 28, 20062006-10-28
Floyd L. Davidson wrote:> Jerry Avins <jya@ieee.org> wrote: >> Randy Yates wrote: >>> floyd@apaflo.com (Floyd L. Davidson) writes: >>>> [...] >>>> digital is usually prefered. The second most significant reason >>>> is the ease with which digital carrier systems can be designed >>>> to trade SNR for bandwidth by using multi-level encoding, which >>>> means well matched adaptions to anything from very noisy fiber >>>> optics to very quiet coax cable. >>> Hmm. Your statement reminds me of getting full-power transfer >>> by >>> matching impedances. Could information transfer be viewed similarly, >>> i.e., by matching the "impedance" of the transmitter to the >>> "impedance" of the channel? > > Yes. That is an interesting comparison. > >> I doubt it. You get as much power as you can when you match the >> load to the source, but you get it at 50% efficiency. >> >> Consider a 12V battery with a .01-ohm internal resistance. With >> There is 6 volts across a matched load, and the total power >> power is 7.2 KW divided equally between the load and the >> battery. (For a short while, anyway.) Moral: matching load to >> source is a good way to avoid reflections. Matching source to >> load is a poor way to deliver power. > > That is *not* an impedance match. It discusses DC resistance, > not impedances. It is not a valid desciption of what happens > with matched vs. unmatched imedpances, and does not compare well > with what was being discussed.Impedances can be pure resistances. You can easily show that a generator with complex impedance Z will deliver maximum power into a load of impedance Z*, where Z and Z* are complex conjugates. Early dynamos were so inefficient that it became common laboratory practice to match the load to them. The electrical load on a dynamo had only slight influence on the load on its prime mover. Dynamos became more powerful and efficient over time, but the practice was retained, and they remained laboratory instruments. Several learned papers showed that wide distribution of electric power was infeasible because the losses in the distribution system far exceeded the deliverable energy. Thomas Edison's first great insight into generation and distribution amounted to discarding the "matched generator" mindset, and that was, to put it aptly, the electrifying departure from received wisdom that made central generating stations possible. (The equalizer bus, which enabled parallel operation of overcompounded -- hence negative-resistance -- dynamos was another example of his genius, but a mere implementation detail.) To get maximum power from a given generator if you dare, match the load to it. To best use energy from the prime source -- steam engine or chemical cell -- make the generator impedance as small as possible. 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 28, 20062006-10-28
Jerry Avins <jya@ieee.org> wrote:>Floyd L. Davidson wrote: >> Jerry Avins <jya@ieee.org> wrote: >>> Randy Yates wrote: >>>> floyd@apaflo.com (Floyd L. Davidson) writes: >>>>> [...] >>>>> digital is usually prefered. The second most significant reason >>>>> is the ease with which digital carrier systems can be designed >>>>> to trade SNR for bandwidth by using multi-level encoding, which >>>>> means well matched adaptions to anything from very noisy fiber >>>>> optics to very quiet coax cable. >>>> Hmm. Your statement reminds me of getting full-power transfer >>>> by >>>> matching impedances. Could information transfer be viewed similarly, >>>> i.e., by matching the "impedance" of the transmitter to the >>>> "impedance" of the channel? >> Yes. That is an interesting comparison. >> >>> I doubt it. You get as much power as you can when you match the >>> load to the source, but you get it at 50% efficiency. >>> >>> Consider a 12V battery with a .01-ohm internal resistance. With >>> There is 6 volts across a matched load, and the total power >>> power is 7.2 KW divided equally between the load and the >>> battery. (For a short while, anyway.) Moral: matching load to >>> source is a good way to avoid reflections. Matching source to >>> load is a poor way to deliver power. >> That is *not* an impedance match. It discusses DC resistance, >> not impedances. It is not a valid desciption of what happens >> with matched vs. unmatched imedpances, and does not compare well >> with what was being discussed. > >Impedances can be pure resistances.That is not the point. With DC there is no such thing as impedance. The above discusses DC, it is *not* discussing impedance matching.>You can easily show that a >generator with complex impedance Z will deliver maximum power >into a load of impedance Z*, where Z and Z* are complex >conjugates.DC load matching and AC impedance matching are not the same... -- Floyd L. Davidson <http://www.apaflo.com/floyd_davidson> Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Reply by ●October 28, 20062006-10-28
Floyd L. Davidson wrote:> Jerry Avins <jya@ieee.org> wrote: > >>Floyd L. Davidson wrote: >> >>>Jerry Avins <jya@ieee.org> wrote: >>> >>>>Randy Yates wrote: >>>> >>>>>floyd@apaflo.com (Floyd L. Davidson) writes: >>>>> >>>>>>[...] >>>>>>digital is usually prefered. The second most significant reason >>>>>>is the ease with which digital carrier systems can be designed >>>>>>to trade SNR for bandwidth by using multi-level encoding, which >>>>>>means well matched adaptions to anything from very noisy fiber >>>>>>optics to very quiet coax cable. >>>>> >>>>>Hmm. Your statement reminds me of getting full-power transfer >>>>>by >>>>>matching impedances. Could information transfer be viewed similarly, >>>>>i.e., by matching the "impedance" of the transmitter to the >>>>>"impedance" of the channel? >>> >>>Yes. That is an interesting comparison. >>> >>> >>>>I doubt it. You get as much power as you can when you match the >>>>load to the source, but you get it at 50% efficiency. >>>> >>>>Consider a 12V battery with a .01-ohm internal resistance. With >>>>There is 6 volts across a matched load, and the total power >>>>power is 7.2 KW divided equally between the load and the >>>>battery. (For a short while, anyway.) Moral: matching load to >>>>source is a good way to avoid reflections. Matching source to >>>>load is a poor way to deliver power. >>> >>>That is *not* an impedance match. It discusses DC resistance, >>>not impedances. It is not a valid desciption of what happens >>>with matched vs. unmatched imedpances, and does not compare well >>>with what was being discussed. >> >>Impedances can be pure resistances. > > > That is not the point. With DC there is no such thing as impedance. > The above discusses DC, it is *not* discussing impedance matching. > > >>You can easily show that a >>generator with complex impedance Z will deliver maximum power >>into a load of impedance Z*, where Z and Z* are complex >>conjugates. > > > DC load matching and AC impedance matching are not the same... >Would you care to defend that erroneous statement?
