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IBOC
I saw a reference to this and wondered what it was. Below is a link I found
using Google: http://www.ibiquity.com/technology/index.htm I can't see how it will do anything but cause serious problems for shortwave, let alone AM. I don't fancy having to replace any radios I have. Since people already have cell phones capable of sending and receiving email, pictures and news, it would seem redundant. What would make people want this over their existing cell phones ? Il Dolce Far Niente |
"Maximus" wrote in message ink.net... I saw a reference to this and wondered what it was. Below is a link I found using Google: http://www.ibiquity.com/technology/index.htm I can't see how it will do anything but cause serious problems for shortwave, let alone AM. There hasn't been any push to use IBOC on shortwave. It's been designed for domestic AM and FM broadcasters. There's a different non-compatible digital standard for shortwave called DRM. I don't fancy having to replace any radios I have. IBOC is sorta compatible with standard AM broadcasting. The standard AM channel is still there, with additional channels of digital modulation just above and below the standard channel. Unfortunately, the fidelity of the standard channel must be reduced, and the digital channels can cause severe interference with adjacent channels. IBOC isn't compatible with DXing stations close in frequency to an IBOC station, and buying another radio won't help. Since people already have cell phones capable of sending and receiving email, pictures and news, it would seem redundant. What would make people want this over their existing cell phones ? Even the "journalists" who do little more than reword corporate press handouts aren't showing much enthusisiam for IBOC broadcasting to cell phones. Anyway, I'd expect the IBOC cell phone broadcasters will be trying FM band transmitters rather than AM band transmitters. There are claims that there is a great unfilled demand for slow text and low-res graphics and pictures on our radios and, by golly, the IBOC folk will step up to the plate and fufill that demand. Imagine that! Pictures on the radio. What will they think of next? Frank Dresser |
I can't see how it will do anything but cause serious problems for shortwave, let alone AM. You won't hear much of anything under 400 mhz once broadband over power lines ramps up to full bore. Do a gOOgle search on BPL, Steve |
"Steve Stone" wrote in message et... You won't hear much of anything under 400 mhz once broadband over power lines ramps up to full bore. Do a gOOgle search on BPL, Steve I'm lazy. How 'bout you gOOgle up some links concerning this "You won't hear much of anything under 400 mhz " business? Oh, yeah. Don't forget to share your knowledge with the TV and radio networks. For some reason, they don't seem concerned. Frank Dresser |
"Frank Dresser" wrote in message ... "Steve Stone" wrote in message et... You won't hear much of anything under 400 mhz once broadband over power lines ramps up to full bore. Do a gOOgle search on BPL, Steve I'm lazy. How 'bout you gOOgle up some links concerning this "You won't hear much of anything under 400 mhz " business? Oh, yeah. Don't forget to share your knowledge with the TV and radio networks. For some reason, they don't seem concerned. 400 MHz is a bit of an exaggeration. BPL will cause considerable interference up to it's limit of 75MHz, and may cause some harmonic interference above that (it IS square wave after all, and high in harmonic content). It won't (or shouldn't) affect the AMBCB, since it is supposed to start at 1.8 MHz. However, there have been several tests performed by hams and some labs (see the ARRL website www.arrl.org), and several countries have already banned BPL because of extreme interference to other services, including HF broadcast and amateur radio services. I don't remember the exact numbers, but basically if you are within 30 feet of a BPL line, you will receive in excess of S9 (some tests have shown 30 dB over S9) of interference. |
"Brenda Ann" wrote in message ... 400 MHz is a bit of an exaggeration. BPL will cause considerable interference up to it's limit of 75MHz, and may cause some harmonic interference above that (it IS square wave after all, and high in harmonic content). Oh, I know. I've done my fair share of usenet posts on the BPL topic. The original poster makes a very good point, though. It is easy to research. It won't (or shouldn't) affect the AMBCB, since it is supposed to start at 1.8 MHz. However, there have been several tests performed by hams and some labs (see the ARRL website www.arrl.org), and several countries have already banned BPL because of extreme interference to other services, including HF broadcast and amateur radio services. I don't remember the exact numbers, but basically if you are within 30 feet of a BPL line, you will receive in excess of S9 (some tests have shown 30 dB over S9) of interference. I really doubt BPL will have any noticable effects on AM/FM/TV reception. After all, the networks haven't used any of their considerable clout in Washington in the BPL fight. I suspect consumer electronics will be most subject to any BPL effects throught the power cord and not the antenna terminals. If this has been a problem in the test areas, I'm not aware of it. But I wonder if BPL will work as promised and if it will be a good deal for the consumers. Power lines are an awfully primitave way to deliver high speed access, and I can imgaine alot of problems. If BPL doesn't work out, the utilities might have to fall back on BWP (Broadband over Water Pipes). Frank Dresser |
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"Brenda Ann" wrote: "Frank Dresser" wrote in message ... "Steve Stone" wrote in message et... You won't hear much of anything under 400 mhz once broadband over power lines ramps up to full bore. Do a gOOgle search on BPL, Steve I'm lazy. How 'bout you gOOgle up some links concerning this "You won't hear much of anything under 400 mhz " business? Oh, yeah. Don't forget to share your knowledge with the TV and radio networks. For some reason, they don't seem concerned. 400 MHz is a bit of an exaggeration. BPL will cause considerable interference up to it's limit of 75MHz, and may cause some harmonic interference above that (it IS square wave after all, and high in harmonic content). It won't (or shouldn't) affect the AMBCB, since it is supposed to start at 1.8 MHz. However, there have been several tests performed by hams and some labs (see the ARRL website www.arrl.org), and several countries have already banned BPL because of extreme interference to other services, including HF broadcast and amateur radio services. I don't remember the exact numbers, but basically if you are within 30 feet of a BPL line, you will receive in excess of S9 (some tests have shown 30 dB over S9) of interference. Data communications occupy wider bandwidths than the stated clock rate. It is not unreasonable to expect harmonics 3 to 5 times the clock rate because the signaling uses square waves and there is significant power in the odd harmonics. -- Telamon Ventura, California |
"Telamon" wrote in message ... Data communications occupy wider bandwidths than the stated clock rate. It is not unreasonable to expect harmonics 3 to 5 times the clock rate because the signaling uses square waves and there is significant power in the odd harmonics. -- Telamon Ventura, California A square wave, itself, won't convey much information. It needs to be modulated, and the modulation would have to effect the symmetry and result in both odd and even harmonics. I don't know what sort of modulation BPL is using. I can imagine hundreds of low amplitude sine wave carriers from 2 to 60 Mhz, all of them phase modulated. In that case, I don't think there would be much harmonic output. This would certainly still be a big problem for the radio hobbyist, but not so much for the FM/TV user. There have been several BPL tests in various communities, and it doesn't seem to have wiped out normal broadcast use. If BPL caused enough bothersome interference to keep people in the test communities from their TVs and radios, the National Association of Broadcasters would have squashed it like a bug. Frank Dresser |
"Frank Dresser" wrote in message ... "Telamon" wrote in message ... Data communications occupy wider bandwidths than the stated clock rate. It is not unreasonable to expect harmonics 3 to 5 times the clock rate because the signaling uses square waves and there is significant power in the odd harmonics. -- Telamon Ventura, California A square wave, itself, won't convey much information. It needs to be modulated, and the modulation would have to effect the symmetry and result in both odd and even harmonics. I don't know what sort of modulation BPL is using. I can imagine hundreds of low amplitude sine wave carriers from 2 to 60 Mhz, all of them phase modulated. In that case, I don't think there would be much harmonic output. Digital comms are purely square waves. The modulation is FSK or similar (generally)... in other words, the on-state is one frequency, the off state is another. This creates a chain of square waves which themselves are not modulated. The bandwidth, in this case 75 MHz, is how many on/off states there are in one second. This is also concurrent with bitrate. Compression schemes can raise the apparent bitrate, however the actual bitrate is the same as the frequency used. I'm not sure how they do the band notching that Japan tried before they tossed out the idea completely. |
"Brenda Ann" wrote in message ... Digital comms are purely square waves. I'm using the term "square wave" to mean a sharp cornered pulse train with an exactly 50% duty cycle. There's not much information there. You've seen one pulse of the square wave, you've seen them all. The modulation is FSK or similar (generally)... in other words, the on-state is one frequency, the off state is another. This creates a chain of square waves which themselves are not modulated. And the square wave is recovered after only after demodulation of the sine waves. The modulation doesn't necessaraly create harmonics, but it does create sidebands. This guy likes to use triangle waves in his illustrations: http://www.cs.ucl.ac.uk/staff/S.Bhat...es/node12.html The bandwidth, in this case 75 MHz, is how many on/off states there are in one second. This is also concurrent with bitrate. Compression schemes can raise the apparent bitrate, however the actual bitrate is the same as the frequency used. The carriers can be both amplitude and phase modulated to increase bitrate. Given that the BPL is usually described as a spread spectrum technology, I'll assume there's many carrier frequencies. I'm not sure how they do the band notching that Japan tried before they tossed out the idea completely. Doesn't Japan have a higher percentage of SWLs and radio amateurs than the US? I don't think most Americans will much care about BPL unless it effects the TV. I'll bet the BPL traps at 3.58 MHz work just fine. Frank Dresser |
From: http://www.qrpis.org/~k3ng/bpl.html ----------- Q: What is intermodulation? A: Intermodulation is the mixing of radio signals which produces new radio signals. Think of it as radio waves having children. But just how do radio waves have children ? This mixing is caused by what are called non-linearities. One non-linear electronic component that you find in most any electronic device is a diode. When multiple radio signals are run through the diode, they mix together. Let's say we have a 4 Mhz signal and a 6 Mhz signal going into the diode. We would then get: 4 + 6 = 10 Mhz 6 ? 4 = 2 Mhz 4 and 6 Mhz had two ?children?, 2 and 10 Mhz ! Now, non-linearities are usually good. This phenomenon is used in just about every radio device to either create a signal to be transmitted, or receive a signal that you hear or see. But, non-linearities can occur where you don't want them and then in causes problems. One such place is in power lines. Bad, corroded connections or dissimilar metals touching can create natural diodes that act like mixers and produce this intermodulation. So, let's take a BPL signal and for the sake of discussion, say it's a grossly simplified consisting of radio signals at 1, 5, 8, 9, and 12 Mhz. Some of the intermodulation products that could be created would be: 1 + 5 = 6 Mhz 8 + 9 = 17 Mhz 9 + 12 = 21 Mhz 12 ? 9 = 3 Mhz But you could also have what is known as third order products: 1 + 9 + 12 = 22 Mhz 8 + 9 + 12 = 29 Mhz 8 ? 5 + 12 = 15 Mhz Or even: 2 * 12 = 24 Mhz (9 ? 5) * 12 = 48 Mhz You can do the math and figure out each permutation, but you get the idea. If we took a real BPL signal that has signals from 1 ? 80 Mhz the number of products and where they would fall are mind-boggling. The resulting intermodulation products in a system could extend well above the band BPL proponents want, falling into FM broadcast, VHF TV, Aeronautical, and more public safety bands. This is just another reason why BPL is so problematic. It's arguable that such non-linearities in power lines are exhibited as arcing connections, something that most power companies are actively searching for these days as the RFI (radio frequency interference) effects are well understood. These maintenance issues will be addressed quickly by well run utilities. However, non-linear loads are common in homes, light dimmers being the first devices that come to mind. Theoretically, these devices could create intermodulation that would in turn be radiated by the house wiring and outside power cabling. |
"Steve Stone" wrote in message et... From: http://www.qrpis.org/~k3ng/bpl.html ----------- Q: What is intermodulation? A: Intermodulation is the mixing of radio signals which produces new radio signals. Think of it as radio waves having children. But just how do radio waves have children ? [snip] Reality trumps theory. BPL is being tested. If BPL was making much in the way of harmonics or IMD products, the low end of the BPL spectrum will be interfering with the high end of the BPL spectrum. The high end of the BPL spectrum would be interfering with TV and FM radio. BPL's fundamentals are the confirmed problem for the radio hobbyist. Ed Hare and other radio amateurs have done alot of work documenting the interference levels on SW radio. Frank Dresser |
It's hard to generalize about all digital communication. I think
BPL is some kind of phase modulated OFDM as Frank says, so in that case you could use essentially rectangular pulses (in practice there is probably some roll-off and guard time to boot). Each individual tone would actually occupy a bandwidth much greater than its keying rate, but since each tone's keying rate is so low compared to the total bandwidth, the net effect is minor, again exactly as Frank says. For single carrier high date rate systems however, the last thing you want to use is rectangular pulses. The spectrum won't have discrete harmonics but it will look like (sin(x)/x)^2 in frequency with significant energy beyond the Nyquist frequency. In those applications a waveform that falls off in time as t^2 is generally used, though there are other options, like minimum-shift keying, which can be looked at either as continuous phase FSK or QPSK using smooth shaped pulses. Continuous phase modulation has some complications though. Oz Brenda Ann wrote: "Frank Dresser" wrote in message ... A square wave, itself, won't convey much information. It needs to be modulated, and the modulation would have to effect the symmetry and result in both odd and even harmonics. I don't know what sort of modulation BPL is using. I can imagine hundreds of low amplitude sine wave carriers from 2 to 60 Mhz, all of them phase modulated. In that case, I don't think there would be much harmonic output. Digital comms are purely square waves. The modulation is FSK or similar (generally)... in other words, the on-state is one frequency, the off state is another. This creates a chain of square waves which themselves are not modulated. The bandwidth, in this case 75 MHz, is how many on/off states there are in one second. This is also concurrent with bitrate. Compression schemes can raise the apparent bitrate, however the actual bitrate is the same as the frequency used. I'm not sure how they do the band notching that Japan tried before they tossed out the idea completely. |
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"Frank Dresser" wrote: "Telamon" wrote in message ... Data communications occupy wider bandwidths than the stated clock rate. It is not unreasonable to expect harmonics 3 to 5 times the clock rate because the signaling uses square waves and there is significant power in the odd harmonics. -- Telamon Ventura, California A square wave, itself, won't convey much information. It needs to be modulated, and the modulation would have to effect the symmetry and result in both odd and even harmonics. I don't know what sort of modulation BPL is using. I can imagine hundreds of low amplitude sine wave carriers from 2 to 60 Mhz, all of them phase modulated. In that case, I don't think there would be much harmonic output. This would certainly still be a big problem for the radio hobbyist, but not so much for the FM/TV user. There have been several BPL tests in various communities, and it doesn't seem to have wiped out normal broadcast use. If BPL caused enough bothersome interference to keep people in the test communities from their TVs and radios, the National Association of Broadcasters would have squashed it like a bug. It is a common error to assume that digital communications are similar to analog RF. One reason is very fast edge times are required to create the most eye margin possible at the decoding end of a data stream so the bandwidth required is much greater. A good rule of thumb is 3.7 times the clock rate as a minimum. Usually the engineering shoots for the fastest edge times practical. An one/zero pattern and multiples thereof are square waves but I should not have used that term because it looks like I just threw you off the path of understanding. -- Telamon Ventura, California |
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Larry Ozarow wrote: It's hard to generalize about all digital communication. I think BPL is some kind of phase modulated OFDM as Frank says, so in that case you could use essentially rectangular pulses (in practice there is probably some roll-off and guard time to boot). Each individual tone would actually occupy a bandwidth much greater than its keying rate, but since each tone's keying rate is so low compared to the total bandwidth, the net effect is minor, again exactly as Frank says. For single carrier high date rate systems however, the last thing you want to use is rectangular pulses. The spectrum won't have discrete harmonics but it will look like (sin(x)/x)^2 in frequency with significant energy beyond the Nyquist frequency. In those applications a waveform that falls off in time as t^2 is generally used, though there are other options, like minimum-shift keying, which can be looked at either as continuous phase FSK or QPSK using smooth shaped pulses. Continuous phase modulation has some complications though. I haven't read how BPL is supposed to work but is it reasonable to expect that a encoding scheme would be used that would shift the spectrum requirements downward so that increased coupling would be needed across the transformers in the power system? -- Telamon Ventura, California |
"Telamon" wrote in message ... It is a common error to assume that digital communications are similar to analog RF. One reason is very fast edge times are required to create the most eye margin possible at the decoding end of a data stream so the bandwidth required is much greater. A good rule of thumb is 3.7 times the clock rate as a minimum. Usually the engineering shoots for the fastest edge times practical. Well, I thought we started out with harmonics of the BPL carriers. I don't see why there would have to be BPL harmonics due to the digital modulation anymore than a RTTY transmission would have to have harmonics. If you're saying the sidebands of carriers will be spaced as far as 3.7 times as far as the data clock rate, sure, why not? I don't know any of the specifics. But if the BPL carriers stop at 80 Mhz, I suppose the total spectrum won't go much past 80 Mhz.. An one/zero pattern and multiples thereof are square waves but I should not have used that term because it looks like I just threw you off the path of understanding. -- Telamon Ventura, California That's the rocky path of understanding, for ya. Can't even take take my shoes off when I need to count past 10. Frank Dresser |
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, "Frank Dresser" wrote: "Telamon" wrote in message ... It is a common error to assume that digital communications are similar to analog RF. One reason is very fast edge times are required to create the most eye margin possible at the decoding end of a data stream so the bandwidth required is much greater. A good rule of thumb is 3.7 times the clock rate as a minimum. Usually the engineering shoots for the fastest edge times practical. Well, I thought we started out with harmonics of the BPL carriers. I don't see why there would have to be BPL harmonics due to the digital modulation anymore than a RTTY transmission would have to have harmonics. If you're saying the sidebands of carriers will be spaced as far as 3.7 times as far as the data clock rate, sure, why not? I don't know any of the specifics. But if the BPL carriers stop at 80 Mhz, I suppose the total spectrum won't go much past 80 Mhz.. An one/zero pattern and multiples thereof are square waves but I should not have used that term because it looks like I just threw you off the path of understanding. -- Telamon Ventura, California That's the rocky path of understanding, for ya. Can't even take take my shoes off when I need to count past 10. No it just that since the data is sent without a clock the data stream regardless of the encoding need fast and precise (low jitter) edge times. Faster edges provide more timing margin. Fast edges have most of the energy in the odd harmonics 1, 3, 5, 7 etc. Most of the energy is in the lowest odd harmonics 1, 3 and 5 being the most important. This explanation only makes sense for a single carrier two level scheme. I do not know what BPL employs but I expect a high frequency scheme be used to reduce the coupling requirements across transformers in the power system. -- Telamon Ventura, California |
"Telamon" wrote in message ... No it just that since the data is sent without a clock the data stream regardless of the encoding need fast and precise (low jitter) edge times. Faster edges provide more timing margin. Fast edges have most of the energy in the odd harmonics 1, 3, 5, 7 etc. Most of the energy is in the lowest odd harmonics 1, 3 and 5 being the most important. This explanation only makes sense for a single carrier two level scheme. Let's say one of the BPL carriers is at 10 Mhz. Let's say it's modulated at 10 khz. If you're saying the modulation is making a channel which covers something like 9.960 Mhz to 10.040 Mhz, that sounds OK to me. If you're saying the modulation creates harmonics at 20, 30, 40 Mhz, I can't see how. I do not know what BPL employs but I expect a high frequency scheme be used to reduce the coupling requirements across transformers in the power system. -- Telamon Ventura, California Power pole transformers should have a nice grounded copper electrostactic shield between the primary and secondary windings. This reduces capacitive coupling between the windings to almost zero. The BPL company will have to bypass the shield with some sort of bandpass coupling. I suppose something as simple as a capacitor would do the job, but they probably have something more elaborate. Maybe they're using a small ferrite transformer with enough insulation to withstand the full primary voltage. Bypassing the power transformer's internal shield would be a lightning hazard. Frank Dresser |
Unfortunately there's no readily available description of
how BPL works, so none of us can really claim he knows exactly what he's talking about. My general understanding is that BPL uses a set of spaced carriers, each modulated at some reasonably low data rate. These carriers are arrayed, I think, over a range like 2MHz to 75 Mz or maybe 2 - 40 or something of that order of magnitude. The transmitted signal is not a pure digital baseband signal - anytime any wideband signal has to propagate over any appreciable distance this can't be used because the medium be it wire or "ether" has a response which varies in frequency, and is not flat enough over the passband of the entire signal bandwidth. There are two broad classes of approach to combatting this (very oversimplified). A single carrier approach takes the baseband signal and uses it to modulate a carrier. This moves the spectrum away from DC which most media don't like (including power lines as you note in the paragraph I've quoted below). The resulting signal would have a natural bandwidth of a modest multiple of the symbol rate as you have noted in another post. Even this is usually too wide in most applications, so the baseband pulses are shaped in time to concentrate them (around DC at baseband, but around the carrier when using the signal to modulate one). This pulse shaping causes the pulses to have very long time durations compared to the signalling interval, but a matched filter is used at the receiver, to re-concentrate the energy temporally. The other broad approach is to use a bunch of evenly spaced RF carriers (as Frank has suggested, and is what I think they actually do). The tones are spaced at frequency intervals of 1/(signalling interval), and the tradeoff between length and frequency spacing is a design decision depending on medium - it does not affect the overall data rate. You can key twice as fast but then carry only half as many tones in a given bandwidth. This is OFDM. In this case, since the signalling rate of each tone is only a small fraction of the total bandwidth the fact that the effective bandwidth of a rectangular pulse is 3 or 5 or whatever times the signalling frequency doesn't effect the total bandwidth by much since the total bandwidth is that of hundreds or thousands of tones. Again, like the case of single carrier, since each tone modulates an RF carrier, there is no LF energy in the resulting signal. Now the medium is roughly flat over the effective BW of each individual tone, and all is basically well. Lastly there was a confusion in the thread between harmonics and excess bandwidth. A randomly modulated square wave does not have discrete harmonics, because the modulation eliminates the periodicity. It does have excess BW as per your discussion of the need for sharp edges. Again in practice the pulses used are not rectangular so the spectrum does not have the ideal (sin(x)/x)^2 roll-off, but something that falls off much more quickly, but there is still significant energy beyond the Nyquist frequency. Oz Telamon wrote: I haven't read how BPL is supposed to work but is it reasonable to expect that a encoding scheme would be used that would shift the spectrum requirements downward so that increased coupling would be needed across the transformers in the power system? |
"Frank Dresser" wrote in message ... Bypassing the power transformer's internal shield would be a lightning hazard. I meant to say that bypassing the internal shield in a simple way could be a lightning hazard. I suppose some kind of opto-isolator would work well. Frank Dresser |
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