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#12
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AM recption notes.
Bob wrote: wrote: Hi Terry - Since you have a hard copy, this may not help that much, but perhaps in the future or for other items that were at this site that you don't have a copy of: There is a website that has archived versions of many websites. It is called the Internet Archive Way Back Machine, and is located at: http://www.archive.org/web/web.php You put in the address of the site and if it has versions of it (in this case it has several) they are displayed for selection. This can help on sites that are active as well. If you want to see something that is no longer there or see the previous version of something that has changed, it will sometimes be there in the archive. Maybe this is something you already know, but if so, maybe it will be helpful to somebody else reading the thread... Bob The archiver works for the firrst set of documents, the OpAmp fitler /combiner page is not found. That sectin had the math discribing the functions. Terry |
#13
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AM recption notes.
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#14
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AM recption notes.
Bob wrote: wrote: The archiver works for the firrst set of documents, the OpAmp fitler /combiner page is not found. That sectin had the math discribing the functions. Here? http://webpages.charter.net/wa1sov/t...s/allpass.html Not trying to be a PITA..... Bob THANKS! For those interested this is one of the most complete treatments of the subject I have found. Terry |
#15
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AM recption notes.
Michael Black wrote: I glanced at it and maybe missed something, but DSB is AM. And he certainly says it at the outset, and when he's talking about the components he's talking about 2 sidebands and a carrier. Now, "DSB" often has fallen into the meaning of "DSB with no carrier", but technically one should specifically define that there is no carrier. snip Michael Back in 1972 when I took my FFC 2nd and 1st class exams DSB was defined as the sidebands with a supressed carrier. A signal with both sidebands and the carrier was simply AM with a BW disgnator. .Now that diffintion may have slipped over the years, but from my perspective AM means both sidebands, with a carier DSB means both sidebands without the carrier, and ISB means two different sidebands with no carrier. I only have received the later, ISB, a very few times mainly on ancient STL links. It might be useful to check out what the ITU says these days about "AM", both sidebands with carrier", and for this conversation, "DSB" being both sidebands without the carrier. Terry |
#16
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AM recption notes.
wrote: Michael Black wrote: I glanced at it and maybe missed something, but DSB is AM. And he certainly says it at the outset, and when he's talking about the components he's talking about 2 sidebands and a carrier. Now, "DSB" often has fallen into the meaning of "DSB with no carrier", but technically one should specifically define that there is no carrier. snip Michael Back in 1972 when I took my FFC 2nd and 1st class exams DSB was defined as the sidebands with a supressed carrier. A signal with both sidebands and the carrier was simply AM with a BW disgnator. .Now that diffintion may have slipped over the years, but from my perspective AM means both sidebands, with a carier DSB means both sidebands without the carrier, and ISB means two different sidebands with no carrier. I only have received the later, ISB, a very few times mainly on ancient STL links. It might be useful to check out what the ITU says these days about "AM", both sidebands with carrier", and for this conversation, "DSB" being both sidebands without the carrier. Terry That high authority, Wikipedia, at http://en.wikipedia.org/wiki/DSB says, "in telecommunications, double-sideband transmission - see also double-sideband suppressed-carrier transmission (DSB-SC) and double-sideband reduced carrier transmission (DSB-RC)". That is supported by ATIS Telecom Glossary 2000 (ANSI approved) at http://www.atis.org/tg2k/ : "DSB: Abbreviation for double sideband. See double-sideband transmission." --- "double-sideband (DSB) transmission: AM transmission in which both sidebands and the carrier are transmitted." and "DSB-SC: Abbreviation for double-sideband suppressed carrier. See double-sideband suppressed-carrier transmission." --- "double-sideband suppressed-carrier (DSB-SC) transmission: Transmission in which (a) frequencies produced by amplitude modulation are symmetrically spaced above and below the carrier frequency and (b) the carrier level is reduced to the lowest practical level, ideally completely suppressed. Note: DSB-SC transmission is a special case of double-sideband reduced carrier transmission." Accordingly, DSB=AM unmodified and AM is the essential first step for its modified variants SSB, ISB, DSB-SC/DSB-RC. Tom |
#17
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AM recption notes.
Tom wrote: wrote: Michael Black wrote: I glanced at it and maybe missed something, but DSB is AM. And he certainly says it at the outset, and when he's talking about the components he's talking about 2 sidebands and a carrier. Now, "DSB" often has fallen into the meaning of "DSB with no carrier", but technically one should specifically define that there is no carrier. snip Michael Back in 1972 when I took my FFC 2nd and 1st class exams DSB was defined as the sidebands with a supressed carrier. A signal with both sidebands and the carrier was simply AM with a BW disgnator. .Now that diffintion may have slipped over the years, but from my perspective AM means both sidebands, with a carier DSB means both sidebands without the carrier, and ISB means two different sidebands with no carrier. I only have received the later, ISB, a very few times mainly on ancient STL links. It might be useful to check out what the ITU says these days about "AM", both sidebands with carrier", and for this conversation, "DSB" being both sidebands without the carrier. Terry That high authority, Wikipedia, at http://en.wikipedia.org/wiki/DSB says, "in telecommunications, double-sideband transmission - see also double-sideband suppressed-carrier transmission (DSB-SC) and double-sideband reduced carrier transmission (DSB-RC)". That is supported by ATIS Telecom Glossary 2000 (ANSI approved) at http://www.atis.org/tg2k/ : "DSB: Abbreviation for double sideband. See double-sideband transmission." --- "double-sideband (DSB) transmission: AM transmission in which both sidebands and the carrier are transmitted." and "DSB-SC: Abbreviation for double-sideband suppressed carrier. See double-sideband suppressed-carrier transmission." --- "double-sideband suppressed-carrier (DSB-SC) transmission: Transmission in which (a) frequencies produced by amplitude modulation are symmetrically spaced above and below the carrier frequency and (b) the carrier level is reduced to the lowest practical level, ideally completely suppressed. Note: DSB-SC transmission is a special case of double-sideband reduced carrier transmission." Accordingly, DSB=AM unmodified and AM is the essential first step for its modified variants SSB, ISB, DSB-SC/DSB-RC. Tom I guess that diffintions aren't static, er fixed. Thanks for the clarification. Terry |
#18
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AM recption notes.
) writes:
Michael Black wrote: I glanced at it and maybe missed something, but DSB is AM. And he certainly says it at the outset, and when he's talking about the components he's talking about 2 sidebands and a carrier. Now, "DSB" often has fallen into the meaning of "DSB with no carrier", but technically one should specifically define that there is no carrier. snip Michael Back in 1972 when I took my FFC 2nd and 1st class exams DSB was defined as the sidebands with a supressed carrier. A signal with both sidebands and the carrier was simply AM with a BW disgnator. .Now that diffintion may have slipped over the years, but from my perspective AM means both sidebands, with a carier DSB means both sidebands without the carrier, and ISB means two different sidebands with no carrier. I only have received the later, ISB, a very few times mainly on ancient STL links. It might be useful to check out what the ITU says these days about "AM", both sidebands with carrier", and for this conversation, "DSB" being both sidebands without the carrier. Terry Are you arguing semantics, or understanding? The post I replied to was almost outraged by that PDF's useage of "DSB". I couldn't figure out whether he was just fussing over words (and thus why was he so outraged?), or really does believe that DSB is not AM. Because people have become sloppy about the words, some of all these conversations about "better AM detectors" is limited. Because people are searching for something that really isn't all that different from what's already available. That PDF talks in terms of how synchronous detectors get too much hype, yet the author turns around and uses everything a "synchronous detector" has except the actual synchronization. But the synchronization isn't actually what provides the potentially improved reception, it's just a means of compensating for some side effects. I never got around to replying, but a few months ago someone started a thread here where he stated something like "So I gather the carrier is more likely to fade when selective fading is happening". I haven't a clue whether the carrier is more likely to fade than the sidebands, but once the carrier fades in relationship to the sidebands you're going to start having reception problems, and once the carrier completely fades you won't be able to recover the modulation. The carrier is the key part to demodulation. But a more universal understanding of "amplitude modulation" would show right away that you can't demodulate a DSB signal unless a carrier is sent along, or generated locally at the receiver end, and selective fading can mean that a DSBc signal sent from the transmitter may be a DSBsc (Double SIdeband suppressed carrier) by the time it reaches the receiver. So in this sort of talk, you'd better start being specific about what you are talking about. Since DSB (with or without a carrier) and SSB (with or without a carrier) are "AM", then you really need to stop using "AM" to only mean DSBc. Hence DSB in the PDF is more descriptive than AM. Is he confused? I don't think so. In his opening paragraph he says "Note: DSB (Double Sideband full-carrier) and SSB (single sideband suppressed carrier) are both amplitude modulation". He defines the term as he is about to use them, so there is no confusion. He needs to use the DSB rather than a more generic "AM" because he is very much thinking in terms of two sidebands (even if he turns around and removes one). The fact that there are two sidebands rather than one may be more significant than whether or not there is a carrier. Since he defined his terms to begin with, any subsequent useage of "DSB" is taken care of. But, again, even if that was not the case, his useage is fine, because whether or not a carrier is sent is irrelevant to his discussion. It's easy to get a locally generated "carrier", and if it's just one sideband it's done all the time, with a bit of mistuning. But with two sidebands, it's far harder. Hence you can either determine where the locally generated carrier needs to be from the the redundant sidebands, or strip off one sideband so it becomes SSB and placing the carrier becomes much easier. Maybe he should have gone with DSBc to show that he is talking about a DSB signal with carrier, but that is hardly a confusion of AM and DSB. As for common useage of so many of these terms, nobody had to specify how many sidebands and whether a carrier went with it until they started to use a subset of that stuff. Look in early articles about SSB and it was pretty common for them to be most specific, ie SSBsc (SSB suppressed carrier). It's only later that it simply became SSB. Nobody really thought of sending DSB without a carrier until SSB came along, and there too it was not uncommon to see it referred to as DSBsc. Michael |
#19
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AM recption notes.
In article . com,
wrote: Tom wrote: wrote: Michael Black wrote: I glanced at it and maybe missed something, but DSB is AM. And he certainly says it at the outset, and when he's talking about the components he's talking about 2 sidebands and a carrier. Now, "DSB" often has fallen into the meaning of "DSB with no carrier", but technically one should specifically define that there is no carrier. Snip Back in 1972 when I took my FFC 2nd and 1st class exams DSB was defined as the sidebands with a supressed carrier. A signal with both sidebands and the carrier was simply AM with a BW disgnator. .Now that diffintion may have slipped over the years, but from my perspective AM means both sidebands, with a carier DSB means both sidebands without the carrier, and ISB means two different sidebands with no carrier. I only have received the later, ISB, a very few times mainly on ancient STL links. It might be useful to check out what the ITU says these days about "AM", both sidebands with carrier", and for this conversation, "DSB" being both sidebands without the carrier. That high authority, Wikipedia, at http://en.wikipedia.org/wiki/DSB says, "in telecommunications, double-sideband transmission - see also double-sideband suppressed-carrier transmission (DSB-SC) and double-sideband reduced carrier transmission (DSB-RC)". That is supported by ATIS Telecom Glossary 2000 (ANSI approved) at http://www.atis.org/tg2k/ : "DSB: Abbreviation for double sideband. See double-sideband transmission." --- "double-sideband (DSB) transmission: AM transmission in which both sidebands and the carrier are transmitted." and "DSB-SC: Abbreviation for double-sideband suppressed carrier. See double-sideband suppressed-carrier transmission." --- "double-sideband suppressed-carrier (DSB-SC) transmission: Transmission in which (a) frequencies produced by amplitude modulation are symmetrically spaced above and below the carrier frequency and (b) the carrier level is reduced to the lowest practical level, ideally completely suppressed. Note: DSB-SC transmission is a special case of double-sideband reduced carrier transmission." Accordingly, DSB=AM unmodified and AM is the essential first step for its modified variants SSB, ISB, DSB-SC/DSB-RC. I guess that diffintions aren't static, er fixed. Thanks for the clarification. Looks to me that acronym DSB does not define the carrier condition. That's why the dash and more letters. -- Telamon Ventura, California |
#20
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AM recption notes.
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