|
AM recption notes.
I found this web page while looking for a nifty audio filter I found
last year. At the very least it gives food for thought. http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf Terry |
AM recption notes.
|
AM recption notes.
Steve wrote: wrote: I found this web page while looking for a nifty audio filter I found last year. At the very least it gives food for thought. http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf Terry There are some helpful hints here, though I'm puzzled by the gripe this fellow has with synchronous detection. I personally wouldn't spend a lot of dough on any receiver that lacked it. I think a lot of people are sour on synchronous detection because they've bought and/or used a receiver that had a very poor implementation of it. When sync detection is done right, as it is on Drake's R8B, then it will sometimes do more to aid reception than all of these hints put together. But the good news is that we don't have to choose between synchronous detection and this fellow's helpful hints. We can have all of these tools at our disposal. Steve My first expousre to SAM was with an AOR7030+. My first impression was that "great". That lead me down a long path toward building my own SAM+ outboard detector. Along the way I had a chance to test a Kiwa, MAOP and the Sherwood SE-3. Both are good and both are much better then the AOR. I tried several designs and settled on a variation of Pete's AD607 SAM. Again at first I was very impressed. However after using it for several months the glammor started to dull. For better then 99% of my AM listening, which in truth is a very small part of my SWL activity as I am into utility, I ofund the 3 OpAmp simple "improved detector" to be the equal or the match for any of the SAMs I had on hand. I was not able to compare the MAP or SE-3 for any extened period and while both are great units, they do have differences. On balance I like the sound quality of the MAP over the SE3, but I liked teh SE3's ability to track rapid, deep fades, espcially with nearby AM signals. I had my feet held to the fire for my posts about Dallas Lankfords observations about the utility of a sharp LP audio filter that chops every thing above ~3 or 4KHz. Exact break point depends on individual choice. Now that I have a R8B, I must admit that this is the best implentation of a SAM I have yet experienced. However in many situations it too can benefit from the AF LP filter. Perhaps I expected too much from SAM detectors. They aren't magic and are far from perfect. The home.worldnet.att.net/~wa1sov/technical/sync_det.html page is no longer up, but Peter C. McNulty, WA1SOV, offered an additional OpAmp fitler design that was reported to allow the AD607 to fully reject unwanted signals via I and Q difference and summing. I don;t have my printed copy in front of me so I can't relate the math. The design appeard to be valid, and several other EEs agreed with his reasoning. However I was never able to get that part of the design to work. I wrote if off in part to the 50Hz minimum tuning step the R2000 offers. His design is clearly worthy of study and I suspect that for someone with more time it could be a winner. At this point I am most interested in reducing the local RF noise, improving my antennas and getting to understand how to get the most from my phaser. Oh, and I am still after the Holly Grail" of a perfect 12V audio amp. Terry |
AM recption notes.
|
AM recption notes.
On Thu, 30 Nov 2006 20:59:40 GMT, Bart Bailey wrote:
In ups.com posted on 30 Nov 2006 06:06:29 -0800, Steve wrote: Begin wrote: I found this web page while looking for a nifty audio filter I found last year. At the very least it gives food for thought. http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf Terry There are some helpful hints here, though I'm puzzled by the gripe this fellow has with synchronous detection. I personally wouldn't spend a lot of dough on any receiver that lacked it. I think a lot of people are sour on synchronous detection because they've bought and/or used a receiver that had a very poor implementation of it. When sync detection is done right, as it is on Drake's R8B, then it will sometimes do more to aid reception than all of these hints put together. But the good news is that we don't have to choose between synchronous detection and this fellow's helpful hints. We can have all of these tools at our disposal. Steve At least the guy gave a thumbs up to the Drake designed SAM in the E1, although it wasn't referred to in his comments about pass band tuning. I use both when conditions are rough, as is sometimes the case with KGO (810) at night, the narrowest 2.3kc IF bandwidth filter combined with a PBT shift of +1.2kc and a USB sync, which allows complete rejection of the local XESPN (800) and shifts the audio to a more balanced sound. The use of wider bandwidth IF filters work fine with SAM on easy conditions like Radio Australia but in a crowd the extra bandwidth tends to allow more of an AGC reduction from the then included but undesirable signals. This is especially true if I'm trying to pick off KKOB (770) from the side of the local powerhouse KFMB (760). FWIW: Local is San Diego and the target stations are; KGO (810) - San Francisco CA KKOB (770) - Albuquerque NM The other local interference station XESPN (800) is in Tijuana MX KFMB 760 S9+15 KKOB 770 S9+10 KKOH 780 S9+15 KABC 790 (out of night pattern) XESPN 800 S9+12 KGO 810 S9+15 All coming in beautifully (except KABC) R8B PreAmp Off 50' Random Wire Lang Station, CA |
AM recption notes.
) writes:
wrote: I found this web page while looking for a nifty audio filter I found last year. At the very least it gives food for thought. http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf Terry Eh, the author confuses DSB and AM. I wouldn't put much faith in his/her analysis. Huh? IN what way? 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. Some of the problem with AM reception discussion is that it was defined in a certain set of terms, for decades and then even for beginners up till recent times (and maybe even today). So they'd define AM as a signal that is amplitude modulated, and that sets things up for the vision that the carrier amplitude goes up and down. Then when SSB became commonplace, instead of going back from the beginning and redefining it all, a separate set of definitions gets tacked on. This leaves people thinking they AM and SSB are two different things, when they are basically the same. Then when discussion of "low distortion AM detectors" comes along, it isn't even clear what people are talking about. Because one is not using a certain type of detector for AM (ie 2 sidebands with a carrier), and a different type for SSB. The talk of "Amplitude Modulation" invokes a vision of a detector that is following the voltage variations of the signal. But that's not the case at all. The carrier mixes with the sideband in the "envelope detector" and that beating is what brings the modulation back down to "baseband". It's just not a good mixer. Listen to an SSB signal without a carrier or BFO. That's the sound of the envelope varying according to the modulating signal, and there's no way to make sense of it without a carrier. No differing loads on the dioded detector, no precision half wave detector (with the diode in a feedback loop), no forward biasing of the diode, can ever make up for the lack of carrier. The carrier of an AM signal is needed to beat with the sidebands and get it back to audio. If the carrier fades in comparison with the sidebands, you start hearing things like that SSB with an "envelope detector", because the carrier is no longer strong enough to mix the sidebands down to audio, and the "envelope detector" is actually following the envelope of the signal. The basic concept of demodulation is no different whether the signal is AM (with carrier), DSB (with no carrier) or SSB (with no carrier). They all need the carrier, or a locally synthesized equivalent, to beat the sideband(s) down to audio. If things were spoken of that way from the beginning, then there'd be less of a leap to the "synchronous detector". No only would a universal set of concepts be applied to all modes, but the point of a synchronous modulator would become clear. A single diode is a lousy mixer. On the other hand, since the carrier of an AM signal comes in with the sidebands, there's no reason for having a second and isolated input for that carrier. But, long ago, people would mess with "exalted carrier reception", which would be the first step up from those "envelope detectors". They'd turn on the Q-multiplier, which had a narrow peak but a wide skirt, and that would boost the incoming carrier in reference to the sidebands, so there was a stronger carrier feeding into the "mixer". It seems that only when SSB came along, and there were design reasons to go to better mixers for the demodulation, that two input mixers started being used, commonly called "product detectors". There were design reasons for going to those, but the basic concept of a locally generated carrier did not require anything more than the single diode "envelope detector". Indeed, the concept had been there back in the days of regen receivers, and every superhet that could be used for CW had a BFO that would feed into the "envelope detector", to give to provide a beat with the incoming signal. I should point out that when the synchronous detector was described in CQ magazine in the late fifties, the actual mixers were single diodes. But once you had product detectors, that opened things up. The notion of boosting the incoming carrier for better mixing action became more clear. I've said before, there was an article in QST about an advanced receiver in the fifties, and it had two parallel IF chains. One wide for voice, the other narrow for CW. But, it also allowed the output of the narrow chain to feed the product detector, and there was the "quasi-synchronous detector" before anyone came up with the name. For AM (with carrier), you had two choices. You could strip off the extra sideband and carrier, then the incoming signal was the same as an SSB signal, and then demodulate it as an SSB signal. This saw a lot of useage in the sixties, when SSB only ham rigs hit the market, and yet AM was still common. People needed a means of demodulating the AM signals, and that worked. While I think it got discussed in the fifties as a better means of AM demodulation, nobody in the sixties was talking that way. It was just a means of demodulating AM signals when there was no means of doing so. (Not only did the SSB-only receivers have narrow IF filters, but often there was no way of turning off the BFO, and the product detectors were a type of mixer that required having that second signal at the second input; without it, you'd get little or no output even with an AM signal that brought it's own carrier.) But if you didn't want to do that, you had to deal with getting the "locally generated carrier" in the right place. Not just so it wouldn't beat against the incoming carrier (when it was strong enough) but if it wasn't placed in the right place, the sidebands would not be translated back to audio in the same places. (So if you sent a 1KHz tone, and the "locally generated carrier" was not right in the middle between those sidebands, one sideband would translate down so that 1KHz tone was 1010Hz while the other would translated down to 990Hz, which would obviously clash with each other.) That's what the "synchronous" bit is about. It's about putting the same sort of BFO that you'd use with SSB (which would feed the same sort of product detector used for SSB), with the addition of circuitry to synchronize the BFO with the carrier of the incoming AM Signal. If the discussion had started with the AM detector as a mixer, then there'd be little magic about "synchronous detectors". The whole process is simply about getting the "carrier" strong in reference to the sidebands, so good mixing happens in the detector. The "synchronous" bit is only a secondary thing, a need because you want the locally generated carrier in the right place. There have always been various means of getting better mixing action at the demodulator. But the important thing has always been about doing that. Michael |
AM recption notes.
Michael Black wrote: ) writes: wrote: I found this web page while looking for a nifty audio filter I found last year. At the very least it gives food for thought. http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf Terry Eh, the author confuses DSB and AM. I wouldn't put much faith in his/her analysis. Huh? IN what way? 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. DSB never has a carrier. There is no such thing as DSB and DSB without a carrier, just DSB. Think of a mixer. If the signal are zero mean, you get DSB. If there is a DC offset on the modulating signal, you get AM. Some of the problem with AM reception discussion is that it was defined in a certain set of terms, for decades and then even for beginners up till recent times (and maybe even today). So they'd define AM as a signal that is amplitude modulated, and that sets things up for the vision that the carrier amplitude goes up and down. Then when SSB became commonplace, instead of going back from the beginning and redefining it all, a separate set of definitions gets tacked on. This leaves people thinking they AM and SSB are two different things, when they are basically the same. No, AM and SSB are different. Then when discussion of "low distortion AM detectors" comes along, it isn't even clear what people are talking about. Because one is not using a certain type of detector for AM (ie 2 sidebands with a carrier), and a different type for SSB. The talk of "Amplitude Modulation" invokes a vision of a detector that is following the voltage variations of the signal. But that's not the case at all. The carrier mixes with the sideband in the "envelope detector" and that beating is what brings the modulation back down to "baseband". It's just not a good mixer. Listen to an SSB signal without a carrier or BFO. That's the sound of the envelope varying according to the modulating signal, and there's no way to make sense of it without a carrier. No differing loads on the dioded detector, no precision half wave detector (with the diode in a feedback loop), no forward biasing of the diode, can ever make up for the lack of carrier. And when did I comment about SSB? The carrier of an AM signal is needed to beat with the sidebands and get it back to audio. If the carrier fades in comparison with the sidebands, you start hearing things like that SSB with an "envelope detector", because the carrier is no longer strong enough to mix the sidebands down to audio, and the "envelope detector" is actually following the envelope of the signal. The basic concept of demodulation is no different whether the signal is AM (with carrier), DSB (with no carrier) or SSB (with no carrier). They all need the carrier, or a locally synthesized equivalent, to beat the sideband(s) down to audio. If things were spoken of that way from the beginning, then there'd be less of a leap to the "synchronous detector". No only would a universal set of concepts be applied to all modes, but the point of a synchronous modulator would become clear. A single diode is a lousy mixer. On the other hand, since the carrier of an AM signal comes in with the sidebands, there's no reason for having a second and isolated input for that carrier. But, long ago, people would mess with "exalted carrier reception", which would be the first step up from those "envelope detectors". They'd turn on the Q-multiplier, which had a narrow peak but a wide skirt, and that would boost the incoming carrier in reference to the sidebands, so there was a stronger carrier feeding into the "mixer". It seems that only when SSB came along, and there were design reasons to go to better mixers for the demodulation, that two input mixers started being used, commonly called "product detectors". There were design reasons for going to those, but the basic concept of a locally generated carrier did not require anything more than the single diode "envelope detector". Indeed, the concept had been there back in the days of regen receivers, and every superhet that could be used for CW had a BFO that would feed into the "envelope detector", to give to provide a beat with the incoming signal. I should point out that when the synchronous detector was described in CQ magazine in the late fifties, the actual mixers were single diodes. But once you had product detectors, that opened things up. The notion of boosting the incoming carrier for better mixing action became more clear. I've said before, there was an article in QST about an advanced receiver in the fifties, and it had two parallel IF chains. One wide for voice, the other narrow for CW. But, it also allowed the output of the narrow chain to feed the product detector, and there was the "quasi-synchronous detector" before anyone came up with the name. For AM (with carrier), you had two choices. You could strip off the extra sideband and carrier, then the incoming signal was the same as an SSB signal, and then demodulate it as an SSB signal. This saw a lot of useage in the sixties, when SSB only ham rigs hit the market, and yet AM was still common. People needed a means of demodulating the AM signals, and that worked. While I think it got discussed in the fifties as a better means of AM demodulation, nobody in the sixties was talking that way. It was just a means of demodulating AM signals when there was no means of doing so. (Not only did the SSB-only receivers have narrow IF filters, but often there was no way of turning off the BFO, and the product detectors were a type of mixer that required having that second signal at the second input; without it, you'd get little or no output even with an AM signal that brought it's own carrier.) But if you didn't want to do that, you had to deal with getting the "locally generated carrier" in the right place. Not just so it wouldn't beat against the incoming carrier (when it was strong enough) but if it wasn't placed in the right place, the sidebands would not be translated back to audio in the same places. (So if you sent a 1KHz tone, and the "locally generated carrier" was not right in the middle between those sidebands, one sideband would translate down so that 1KHz tone was 1010Hz while the other would translated down to 990Hz, which would obviously clash with each other.) That's what the "synchronous" bit is about. It's about putting the same sort of BFO that you'd use with SSB (which would feed the same sort of product detector used for SSB), with the addition of circuitry to synchronize the BFO with the carrier of the incoming AM Signal. If the discussion had started with the AM detector as a mixer, then there'd be little magic about "synchronous detectors". The whole process is simply about getting the "carrier" strong in reference to the sidebands, so good mixing happens in the detector. The "synchronous" bit is only a secondary thing, a need because you want the locally generated carrier in the right place. There have always been various means of getting better mixing action at the demodulator. But the important thing has always been about doing that. Michael Christ all mighty, what is with the verbal diarrhea? You are trying to analyze modulation by looking at demodulation. This is wrong thinking. You analyze modulation by looking at modulators. AM: One mixer. Feed it a carrier and signal. The carrier is zero mean. The signal has a DC bias sufficient that the signal always remains positive. Congrats, you gave birth to AM. DSB: One mixer: Feed it zero mean carrier and signal. Out pops DSB. SSB: Slightly more complicated since it involves Hilbert transformers and quadrature mixers. I can do an explanation, but it might take a paragraph. My original comment still stands. The author of the paper confused AM and DSB. |
AM recption notes.
In article .com,
"Steve" wrote: wrote: I found this web page while looking for a nifty audio filter I found last year. At the very least it gives food for thought. http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf Terry There are some helpful hints here, though I'm puzzled by the gripe this fellow has with synchronous detection. I personally wouldn't spend a lot of dough on any receiver that lacked it. I think a lot of people are sour on synchronous detection because they've bought and/or used a receiver that had a very poor implementation of it. When sync detection is done right, as it is on Drake's R8B, then it will sometimes do more to aid reception than all of these hints put together. But the good news is that we don't have to choose between synchronous detection and this fellow's helpful hints. We can have all of these tools at our disposal. Some of it is regional reception patterns, ax grinding, ignorance, and some of it is just plain nut case thinking focusing on the negative aspects because the sync circuit in radios are not perfect and ignoring the good performance that results most of the time. Listening to AMBCB in the car where I don't have a sync detector and home where I do sure makes me wish I had it in the car. I'm not talking about some small improvement I'm talking huge. Without sync you can have a strong but completely unintelligible signal for a few seconds to a few minutes a lot of the time in the evenings on any station not right in town or more than 50 miles away or in other words most stations. Usually the distortion is more like a few seconds length on SW but whether you miss a few words or miss whole paragraphs of the conversation it is very annoying. It depends on conditions of course but when you have selective fading turning on the sync detector makes an absolutely huge difference in reception even with the Sony 7600 portable. And of course if you have side band selectable sync detection with another station or local noise source generating interference to one side of a station you want to receive usually results in near 100% rejection of the offender by selecting the opposite side band. It's as close to a magic improvement in reception you are going to get on a radio. Again this results in a huge non-arguable difference in reception quality. The improvement in reception most radios have with sync detection is huge not small and so the improvement is not open to argument. People that argue about it are being stupid. People can write anything on Usenet or on a web page and a lot of it is crapola. -- Telamon Ventura, California |
AM recption notes.
In article ,
"Brenda Ann" wrote: "Michael Black" wrote in message ... ) writes: wrote: I found this web page while looking for a nifty audio filter I found last year. At the very least it gives food for thought. http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf Terry Eh, the author confuses DSB and AM. I wouldn't put much faith in his/her analysis. Huh? IN what way? 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. Some of the problem with AM reception discussion is that it was defined in a certain set of terms, for decades and then even for beginners up till recent times (and maybe even today). So they'd define AM as a signal that is amplitude modulated, and that sets things up for the vision that the carrier amplitude goes up and down. Then when SSB became commonplace, instead of going back from the beginning and redefining it all, a separate set of definitions gets tacked on. This leaves people thinking they AM and SSB are two different things, when they are basically the same. Then when discussion of "low distortion AM detectors" comes along, it isn't even clear what people are talking about. Because one is not using a certain type of detector for AM (ie 2 sidebands with a carrier), and a different type for SSB. The talk of "Amplitude Modulation" invokes a vision of a detector that is following the voltage variations of the signal. But that's not the case at all. The carrier mixes with the sideband in the "envelope detector" and that beating is what brings the modulation back down to "baseband". It's just not a good mixer. Listen to an SSB signal without a carrier or BFO. That's the sound of the envelope varying according to the modulating signal, and there's no way to make sense of it without a carrier. No differing loads on the dioded detector, no precision half wave detector (with the diode in a feedback loop), no forward biasing of the diode, can ever make up for the lack of carrier. The carrier of an AM signal is needed to beat with the sidebands and get it back to audio. If the carrier fades in comparison with the sidebands, you start hearing things like that SSB with an "envelope detector", because the carrier is no longer strong enough to mix the sidebands down to audio, and the "envelope detector" is actually following the envelope of the signal. The basic concept of demodulation is no different whether the signal is AM (with carrier), DSB (with no carrier) or SSB (with no carrier). They all need the carrier, or a locally synthesized equivalent, to beat the sideband(s) down to audio. If things were spoken of that way from the beginning, then there'd be less of a leap to the "synchronous detector". No only would a universal set of concepts be applied to all modes, but the point of a synchronous modulator would become clear. A single diode is a lousy mixer. On the other hand, since the carrier of an AM signal comes in with the sidebands, there's no reason for having a second and isolated input for that carrier. But, long ago, people would mess with "exalted carrier reception", which would be the first step up from those "envelope detectors". They'd turn on the Q-multiplier, which had a narrow peak but a wide skirt, and that would boost the incoming carrier in reference to the sidebands, so there was a stronger carrier feeding into the "mixer". It seems that only when SSB came along, and there were design reasons to go to better mixers for the demodulation, that two input mixers started being used, commonly called "product detectors". There were design reasons for going to those, but the basic concept of a locally generated carrier did not require anything more than the single diode "envelope detector". Indeed, the concept had been there back in the days of regen receivers, and every superhet that could be used for CW had a BFO that would feed into the "envelope detector", to give to provide a beat with the incoming signal. I should point out that when the synchronous detector was described in CQ magazine in the late fifties, the actual mixers were single diodes. But once you had product detectors, that opened things up. The notion of boosting the incoming carrier for better mixing action became more clear. I've said before, there was an article in QST about an advanced receiver in the fifties, and it had two parallel IF chains. One wide for voice, the other narrow for CW. But, it also allowed the output of the narrow chain to feed the product detector, and there was the "quasi-synchronous detector" before anyone came up with the name. For AM (with carrier), you had two choices. You could strip off the extra sideband and carrier, then the incoming signal was the same as an SSB signal, and then demodulate it as an SSB signal. This saw a lot of useage in the sixties, when SSB only ham rigs hit the market, and yet AM was still common. People needed a means of demodulating the AM signals, and that worked. While I think it got discussed in the fifties as a better means of AM demodulation, nobody in the sixties was talking that way. It was just a means of demodulating AM signals when there was no means of doing so. (Not only did the SSB-only receivers have narrow IF filters, but often there was no way of turning off the BFO, and the product detectors were a type of mixer that required having that second signal at the second input; without it, you'd get little or no output even with an AM signal that brought it's own carrier.) But if you didn't want to do that, you had to deal with getting the "locally generated carrier" in the right place. Not just so it wouldn't beat against the incoming carrier (when it was strong enough) but if it wasn't placed in the right place, the sidebands would not be translated back to audio in the same places. (So if you sent a 1KHz tone, and the "locally generated carrier" was not right in the middle between those sidebands, one sideband would translate down so that 1KHz tone was 1010Hz while the other would translated down to 990Hz, which would obviously clash with each other.) That's what the "synchronous" bit is about. It's about putting the same sort of BFO that you'd use with SSB (which would feed the same sort of product detector used for SSB), with the addition of circuitry to synchronize the BFO with the carrier of the incoming AM Signal. If the discussion had started with the AM detector as a mixer, then there'd be little magic about "synchronous detectors". The whole process is simply about getting the "carrier" strong in reference to the sidebands, so good mixing happens in the detector. The "synchronous" bit is only a secondary thing, a need because you want the locally generated carrier in the right place. There have always been various means of getting better mixing action at the demodulator. But the important thing has always been about doing that. Michael Damn good explanation, Michael. And 100% accurate. He always writes good posts. -- Telamon Ventura, California |
AM recption notes.
On Fri, 01 Dec 2006 08:43:43 GMT, Bart Bailey wrote:
Interesting that KABC (790) isn't heard in your area. Not as strong as KNX (1070) but definitely good copy here. What do you hear at 1MHz? KCEO - Escondido or KOMO - Seattle You're between them. I can only get a co-channel mix here in town but if I go up to Mt Laguna, about 40 miles east, then the loop separates them nicely. Also on occasions there's an unknown co-channel MX station under KGO that the loop can't separate from here. Haven't tried it on the hill yet. I can hear KABC, plus another station and they fight with each other and the KABC skywave. KOMO 1000 is always there, almost like fringe groundwave. I think it may be ducting along the coast. There's a ''TIS'' station at UCLA on 810; more of a problem than the Mexican. |
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 |
AM recption notes.
|
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 |
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 |
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 |
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 |
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 |
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 |
AM recption notes.
|
AM recption notes.
Michael Black wrote: ) 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? It is not sematics, but generally agreed upon definitions. 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. I just don't buy the argument that nobody thought about DSB. DSB is naturally generated from a mixer if the audio signal is zero mean. [Again, it is best to talk about modulation schemes by discussion modulators.] Remember, AM exists because the demod is cheaper, not because it is any easier to generate that say DSB. AM and DSB use the same hardware. Michael To get to the meat of the problem, the only utility in any of these demod schemes is if you can narrow band the signal. That is, just because you can build a demodulator that can use both sidebands without need of the carrier, it doesn't mean the quality of the signal will be any better. Wider bandwidth signals are more prone to atmospheric effects, i.e. fading. Thus if you are going to do synchronous detection, you need to receive one side band, period. |
AM recption notes.
Brenda Ann wrote: wrote in message ups.com... 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. No arguments from me. That was how I was taught in college, though ISB was never a topic. ISB (with carrier) has been around for a while. It was used in one of the original AM Stereo experiments. I believe it was Kahn that was using it. The only station I know of personally that used it commercially was XETRA, and it actually didn't do too badly, but you needed either a special receiver or two radios to tune the two sidebands to receive stereo. It was not a compatible system though in the sense that on a single standard AM radio, you only heard the channel (perhaps with some spillover depending on tuning) that the radio was designed to demodulate. When you study communications in a university, it tends to be pure theory rather than some specific protocol. While this seems counter-intuitive, understanding the theory means you can figure out some proprietary standard when the time comes. The only exceptions that come to mind would be something like duobinary modulation, which I think was a GTE patent, though it was treated as something generic. So getting back to ISB, it never came up, though by your description it is a matter of pulling out the sideband independently. So if you understand SSB, ISB would follow. |
AM recption notes.
On Sun, 03 Dec 2006 01:10:52 GMT, Telamon
wrote: clarification. Looks to me that acronym DSB does not define the carrier condition. That's why the dash and more letters. FCC EMISSION DESIGNATORS Detailed List Last Rev. 1998 WARC-79, the World Administrative Radio Conference that rewrote many of the world's radio regulations, adopted a new system of emission classification. The traditional A (Amplitude), F (Frequency), and P (Pulse) was intuitive, but limited and clumsy when dealing with new modes. The world's radio bodies, including the FCC, gradually phased in the new system until today it completely replaces the old one. The formula for the new designations, loosely from ITU radio regulations 264 through 273, and Appendix 6, Part A, is: [BBBB]MNI[DM], where [] means optional when writing emission specs. [BBBB] = Necessary Bandwidth (shown in FCC records, but is often omitted elsewhere) Uses a letter and three numbers. The letter goes where the decimal point should be placed, and denotes a magnitude: H Hz K kHz M MHz G GHz Some common bandwidths a 400 Hz 400H 2.4 kHz 2K40 12.5 kHz 12K5 6 MHz 6M00 M = Modulation Type N None A AM (Amplitude Modulation), double sideband, full carrier H AM, single sideband, full carrier R AM, single sideband, reduced or controlled carrier J AM, single sideband, suppressed carrier B AM, independent sidebands C AM, vestigial sideband (commonly analog TV) F Angle-modulated, straight FM G Angle-modulated, phase modulation (common; sounds like FM) D Carrier is amplitude and angle modulated P Pulse, no modulation K Pulse, amplitude modulation (PAM, PSM) L Pulse, width modulation (PWM) M Pulse, phase or position modulation (PPM) Q Pulse, carrier also angle-modulated during pulse W Pulse, two or more modes used X All cases not covered above N = Nature of modulating signal 0 None 1 Digital, on-off or quantized, no modulation 2 Digital, with modulation 3 Single analog channel 7 Two or more digital channels 8 Two or more analog channels 9 Composite, one or more digital channel, one or more analog X All cases not covered above I = Information type N None A Aural telegraphy, for people (Morse code) B Telegraphy for machine copy (RTTY, fast Morse) C Analog fax D Data, telemetry, telecommand E Telephony, voice, sound broadcasting F Video, television W Combinations of the above X All cases not covered above [DM] = additional details, not used by FCC, optional elsewhere D = Detail RTTY/modems: A Two condition code, differing numbers or durations (Morse) B Two condition code, same number and duration, no error check C Two condition code, same num & dur, error check D Four condition code, 1 or more bits per condition E Multi condition code, 1 or more bits per condition F Multi condition code, conditions may combine Audio: G Broadcast quality (mono) H Broadcast quality (stereo/multichannel) J Commercial quality K Commercial quality, analog freq inversion or band scrambling L Commercial quality, FM pilot tone (i.e. Lincomprex) Video: M Monochrome N Color W Combination X All cases not covered above M = Multiplex type N None C Code division F Frequency division T Time division W Combination of above X All other types ----------------------------------------------------------------------- Converting Between Old & New Systems ----------------------------------------------------------------------- USE OLD NEW Pure carrier A0,F0 N0N Morse telegraphy (by ear) A1 A1A Modulated CW Morse A2 A2A AM voice A3 A3E SSB, suppressed carrier A3J J3E SSB, reduced carrier A3R R3E SSB, full carrier A3H H3E Television A5 C3F RTTY (F.S.K.) F1 F1B RTTY (A.F.S.K.) F2 F2B FM voice (Narrowband) F3 F3E, 20K0F3E Packet Data/Teleprinters with Audio Sub-Carrier 20F2 20K0F2B Data with Audio Sub-carrier 3F2 3K00F2D 6F2 6K00F2D 20F2 20K0F2D Analog Voice 20F3 20K0F3E Digital Voice 20F3Y 20K0F1E Digital Facsimile without Audio Sub-Carrier 20F4 20K0F1C Digital Facsimile with Audio Sub-Carrier 20F4 20K0F2C Analog Facsimile 20F4 20K0F3C Composite of Digital & Analog Information 3F9 3K00F9W 6F9 6K00F9W 20F9 20K0F9W Packet Data/Teleprinters without Audio Sub-Carrier 20F9Y 20K0F1B Digital Data 20F9Y 20K0F1D LAND MOBILE EMISSIONS MICROWAVE EMISSIONS old new old new old new A0 N0N P0 P0N F9 F8W (If bw is less than A1 A1A P9 P0N 50 convert to F2D) A3 A3E A2J J2B F9Y F7W (If bw is less than A3J J3E A3H H3E 50 convert to F2D) A7J J8W A9J J9W F3 F3E A9 A9W P1 P1D A9Y A7W A9Y A1D F2Y F2D A5 A3F F0 N0N A0H H0N A9 A8W F1 F1B A7 A8D A5C C3F F2 F2D F7 F8D F2 F2D F3 F3E F5 F3F F3Y F1E F4 F3C F9 F9W F9Y F1D A2H H2D A2 A2D ---------------------------------------------------------------------- And here is the relevant section of FCC rules: ---------------------------------------------------------------------- From General Docket No. 80-739 Section 2.201 Emission, modulation, and transmission characteristics. The following system of designating emission, modulation, and transmission characteristics shall be employed. (a) Emissions are designated according to their classification and their necessary bandwidth. (b) A minimum of three symbols are used to describe the basic characteristics of radio waves. Emissions are classified and symbolized according to the following characteristics: (1) First symbol - type of modulation of the main carrier; (2) Second Symbol - nature of signal(s) modulating the main carrier; (3) Third symbol - type of information to be transmitted. NOTE: A fourth and fifth symbol are provided for additional information and are shown in Appendix 6, Part A of the ITU Radio Regulations. Use of the fourth and fifth symbol is optional. Therefore, the symbols may be used as described in Appendix 6, but are not required by the Commission. (c) First Symbol - types of modulation of the main carrier: (1) Emission of an unmodulated carrier N (2) Emission in which the main carrier is amplitude- modulated (including cases where sub-carriers are angle modulated): - Double-sideband A - Single-sideband, full carrier H - Single-sideband, reduced or variable level carrier R - Single-sideband, suppressed carrier J - Independent sidebands B - Vestigial sideband C (3) Emission in which the main carrier is angle-modulated: - Frequency modulation F - Phase modulation G NOTE: Whenever frequency modulation "F" is indicated, Phase modulation "G" is also acceptable. (4) Emission in which the main carrier is amplitude and angle-modulated either simultaneously or in a pre- established sequence D (5) Emission of pulses:* - Sequence of unmodulated pulses P - A sequence of pulses: - Modulated in amplitude K - Modulated in width/duration L - Modulated in position/phase M - In which the carrier is angle-modulated during the period of the pulse Q - Which is a combination of the foregoing or is produced by other means V (6) Cases not covered above, in which an emission consists of the main carrier modulated, either simultaneously or in a pre-established sequence, a combination of two or more of the following modes: amplitude, angle, pulse W (7) Cases not otherwise covered X *Emissions where the main carrier is directly modulated by a signal which has been coded into quantizied form (e.g., pulse code modulation) should be designated under (2) or (3). (d) Second Symbol- nature of signal(s) modulating the main carrier: (1) No modulating signal 0 (2) A single channel containing quantized or digital information without the use of a modulating sub- carrier, excluding time-division multiplex 1 (3) A single channel containing quantized or digital information with the use of a modulating sub-carrier, excluding time-division multiplex 2 (4) A single channel containing analogue information 3 (5) Two or more channels containing quantized or digital information 7 (6) Two or more channels containing analogue information 8 (7) Composite system with one or more channels containing quantized or digital information, to-gether with one or more channels containing analogue information 9 (8) Cases not otherwise covered X (e) Third Symbol - type of information to be transmitted: (1) No information transmitted N (2) Telegraphy - for aural reception A (3) Telegraphy - for automatic reception B (4) Facsimile C (5) Data transmission, telemetry, telecommand D (6) Telephony (including sound broadcasting) E (7) Television (video) F (8) Combination of the above W (9) Cases not otherwise covered X (f) Type B emission: As an exception to the above principles, damped waves are symbolized in the Commission's rules and regulations as type B emission. The use of type B emissions is forbidden. (g) Whenever the full designation of an emission is necessary, the symbol for that emission, as given above, shall be preceded by the necessary bandwidth of the emission as indicated in Section 2.202 (b) (1). Section 2.202 Bandwidths. (b) Necessary bandwidths. (1) The necessary bandwidth shall be expressed by three numerals and one letter. The letter occupies the position of the decimal point and represents the unit of bandwidth. The first character shall be neither zero nor K, M or G. - -end- |
AM recption notes.
In article . com,
wrote: I just don't buy the argument that nobody thought about DSB. DSB is naturally generated from a mixer if the audio signal is zero mean. [Again, it is best to talk about modulation schemes by discussion modulators.] Remember, AM exists because the demod is cheaper, not because it is any easier to generate that say DSB. AM and DSB use the same hardware. But there's something where a DSB local carrier has to be in phase with the signal, otherwise there some sort of canceling effect from the two sidebands. SSB doesn't have the problem, it just causes a pitch shift. The only DSB I know of, (that isn't just treated as a cheap form of SSB, where really only one sideband is used) is the L-R subcarrier in FM stereo where they double the pilot tone to get an in phase carrier. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) |
AM recption notes.
Mark Zenier wrote: In article . com, wrote: I just don't buy the argument that nobody thought about DSB. DSB is naturally generated from a mixer if the audio signal is zero mean. [Again, it is best to talk about modulation schemes by discussion modulators.] Remember, AM exists because the demod is cheaper, not because it is any easier to generate that say DSB. AM and DSB use the same hardware. But there's something where a DSB local carrier has to be in phase with the signal, otherwise there some sort of canceling effect from the two sidebands. SSB doesn't have the problem, it just causes a pitch shift. I've done DSB generation in a baseband signal for a telemetry application, similar to the FM stereo demod, i.e a pilot was provided. However, say you had no pilot and you were simply tuning by hand. Assume a simple mixer. If you were off a bit, the sound would be pretty ugly, i.e. 1000hz would be a combination of 999hz and 1001Hz if you were off by 1Hz in the local carrier. However, I could see this making tuning very easy since if you were off a little, it would be clear that the local carrier needed adjusting. The only DSB I know of, (that isn't just treated as a cheap form of SSB, where really only one sideband is used) is the L-R subcarrier in FM stereo where they double the pilot tone to get an in phase carrier. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) |
AM recption notes.
Miso:
Eh, the author confuses DSB and AM. I wouldn't put much faith in his/her analysis. I wouldn't put much faith in someone who is confused over the gender of the name 'Phil'. Ludicrous and a "poisoning the well" logic fallacy. DSB never has a carrier. There is no such thing as DSB and DSB without a carrier, just DSB. http://www.atis.org/tg2k/_double-sid...nsmission.html http://www.atis.org/tg2k/_double-sid...nsmission.html http://www.atis.org/tg2k/_amplitude_modulation.html Telamon: Listening to AMBCB in the car where I don't have a sync detector and home where I do sure makes me wish I had it in the car. See my article "ferrite rods make poor car antennas". The improvement in reception most radios have with sync detection is huge not small and so the improvement is not open to argument. Is SAM on your RX340 a huge improvement over SSB? (Yes it's a trap.) Happy Holidays! phil :) http://groups.yahoo.com/group/phils_radio_articles/ [Files Only] |
AM recption notes.
In article .com,
wrote: Miso: Eh, the author confuses DSB and AM. I wouldn't put much faith in his/her analysis. I wouldn't put much faith in someone who is confused over the gender of the name 'Phil'. Ludicrous and a "poisoning the well" logic fallacy. DSB never has a carrier. There is no such thing as DSB and DSB without a carrier, just DSB. http://www.atis.org/tg2k/_double-sid...nsmission.html http://www.atis.org/tg2k/_double-sid...nsmission.html http://www.atis.org/tg2k/_amplitude_modulation.html Telamon: Listening to AMBCB in the car where I don't have a sync detector and home where I do sure makes me wish I had it in the car. See my article "ferrite rods make poor car antennas". Where? At Yahoo? I'm not a member. The improvement in reception most radios have with sync detection is huge not small and so the improvement is not open to argument. Is SAM on your RX340 a huge improvement over SSB? (Yes it's a trap.) SSB on the RX340 is superb. SAM works great most of the time. The SAM does have the locking problem when you encounter rapid deep fades the AGC system in the radio can't seem to handle properly. In those cases you can usually fiddle with the programmable AGC settings to get an acceptable response. Only other solution is to use an antenna less susceptible to rapid fading. That would be one with larger cross sectional area. The SAM can lock on very weak signals and is side band selectable so with DSP filtering it usually makes adjacent channel splatter disappear. SAM usually works like a champ. You really get really excellent sound from this radio as you can increase the bandwidth as conditions allow for SSB or AM. -- Telamon Ventura, California |
AM recption notes.
wrote: Miso: Eh, the author confuses DSB and AM. I wouldn't put much faith in his/her analysis. I wouldn't put much faith in someone who is confused over the gender of the name 'Phil'. Ludicrous and a "poisoning the well" logic fallacy. "phil" is in the file name, not the document. DSB never has a carrier. There is no such thing as DSB and DSB without a carrier, just DSB. Oh sure, you read it on the net, so it must be right. I stand by my statements. Just because a few people get it wrong on the net, doesn't make it right. I've seen DSBAM used for AM, DSBSC used for DSB. Check out this college text: http://www.utdallas.edu/~mtacca/cour...-2006/Exp3.pdf In the equation, you would have to add a DC bias in x(t) to produce AM. Hence they are producing DSB, pure and simple. http://www.atis.org/tg2k/_double-sid...nsmission.html http://www.atis.org/tg2k/_double-sid...nsmission.html http://www.atis.org/tg2k/_amplitude_modulation.html Telamon: Listening to AMBCB in the car where I don't have a sync detector and home where I do sure makes me wish I had it in the car. See my article "ferrite rods make poor car antennas". The improvement in reception most radios have with sync detection is huge not small and so the improvement is not open to argument. Is SAM on your RX340 a huge improvement over SSB? (Yes it's a trap.) Happy Holidays! phil :) http://groups.yahoo.com/group/phils_radio_articles/ [Files Only] |
AM recption notes.
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AM recption notes.
Just because a few people get it wrong on the net, doesn't make it
right. I've seen DSBAM used for AM, DSBSC used for DSB. Check out this college text: i agree: version 2 will use "DSBc". why the logic fallacy? if you can find errors in my analysis e-mail me. ~phil :) PS my name -is- in the paper and 999/1001 Hz tones sound the -same-. |
AM recption notes.
Michael Black wrote: ) writes: Just because a few people get it wrong on the net, doesn't make it right. I've seen DSBAM used for AM, DSBSC used for DSB. Check out this college text: http://www.utdallas.edu/~mtacca/cour...-2006/Exp3.pdf In the equation, you would have to add a DC bias in x(t) to produce AM. Hence they are producing DSB, pure and simple. The only reason you'd need a DC bias on the transmitting mixer is if the mixer was of a balanced type. IN that case, the DC bias unbalances the mixer, allowing for the carrier to get through to the output. But, long before balanced mixers came along, there were lots of mixers that let the carrier through. Hence to get DSBc you'd either need an inherently unbalanced mixer at the transmitter end, or if it is a balanced mixer of some sort, unbalance it, with a DC bias or messing with the balance of the circuit. (It is often easier to apply a DC voltage, but it's not the only way). Of course, you don't even need a balanced mixer to send DSBsc. You could notch out the carrier at the output of the mixer. Just put a very sharp filter there, that only gets rid of the carrier but not the sidebands. Not even close to a common practice, but I've seen it played with. I've also seen SSB transmitters that started with a balanced mixer, but also used a single crystal notch filter at the output of that mixer, to increase carrier suppression; in the days of tubes the balance of the mixer sometimes varied with temperature (and wear) and the filter just guaranteed good carrier suppresion. Let's not forget that early experiments with SSB used a very low carrier frequency, and used the low bandwidth of the antenna to filter out the carrier and the extra sideband. Obviously a filter (the antenna) was used to get rid of the unwanted sideband, but it was also used to get rid of the carrier. The transmitter was simply a DSBc transmitter, as seen on the "AM broadcast band" today. Michael It never ever ends. You do not need to talk about mixer designs to describe modulation. It is handy since most people that studies communications can look at a signal flow graph and visualize the modulation. However, you can explain double side band simply from trig identities. In communications, you do the theory, then build the hardware. Those who do it backwards eventually get screwed. cos(a)*cos(b)=0.5*(cos(a-b) +cos(a+b)) Make cos(a) here is the message, while cos(b) is the carrier. In this case you get two tones, i.e. the sum and difference frequencies that are located above and below the carrier. Why, it's like, dare I say, double sideband! Hence DSB is all you need. There is no carrier to suppress. |
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