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AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
isw wrote:
What is the difference between AM and DSB? AM is a process. DSB (double sideband), with carrier, is it's most simple result. DSB without carrier (suppressed carrier dsb) requires using, at least, a balanced mixer as the AM multiplier. And requires, for proper reception, that a carrier be recreated at the receiver which has not only the amplitude of the original, but also its exact phase. Absent some sort of "pilot" to get things synchronized, this makes reception very difficult. Isaac Try a Costas loop. |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
On Thu, 05 Jul 2007 00:00:45 -0700, Ron Baker, Pluralitas! wrote:
Suppose you have a 1 MHz sine wave whose amplitude is multiplied by a 0.1 MHz sine wave. What would it look like on an oscilloscope? This is close, but not to scale: http://en.wikipedia.org/wiki/Amplitude_modulation The animation shows the "envelope". What would it look like on a spectrum analyzer? One vertical "spike" at 1 MHz with smaller spikes at .9 and 1.1 MHz. The height of the two side spikes, depends on the depth of modulation. In this case, the carrier is in the middle, and the sidebands are on the sides. Then suppose you have a 1.1 MHz sine wave added to a 0.9 MHz sine wave. What would that look like on an oscilloscope? whatever 0.9 MHz superimposed on 1.1 MHz looks like. ;-) What would that look like on a spectrum analyzer? One spike at each input frequency, 0.9 and 1.1 MHz. If they're mixed nonlinearly, then you get modulation, as above. Hope This Helps! Rich |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Thu, 05 Jul 2007 20:02:15 -0600, Bob Myers wrote:
"John Fields" wrote in message You missed my point, which was that in a mixer (which the ear is, since its amplitude response is nonlinear) as the two carriers approach each other the difference frequency will go to zero and the sum frequency will go to the second harmonic of either carrier, making it largely appear to vanish into the fundamental. Sorry, John - while the ear's amplitude response IS nonlinear, it does not act as a mixer. "Mixing" (multiplication) occurs when a given nonlinear element (in electronics, a diode or transistor, for example) is presented with two signals of different frequencies. But the human ear doesn't work in that manner - there is no single nonlinear element which is receiving more than one signal. Sure there is - the cochlea. (well, the whole middle ear/inner ear system.) What would the output look like if you summed a 300Hz tone and a 400Hz tone and sent the sum to a log amp and spectrum analyzer/fft? Thanks, Rich |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
On 7/4/07 8:42 PM, in article , "Ron
Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 10:16 AM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 7:52 AM, in article , "Ron Baker, Pluralitas!" wrote: snip cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b]) Basically: multiplying two sine waves is the same as adding the (half amplitude) sum and difference frequencies. No, they aren't the same at all, they only appear to be the same before they are examined. The two sidebands will not have the correct phase relationship. What do you mean? What is the "correct" relationship? One could, temporarily, mistake the added combination for a full carrier with independent sidebands, however. (For sines it is sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b]) = 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees]) = 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees]) ) -- rb When AM is correctly accomplished (a single voiceband signal is modulated The questions I posed were not about AM. The subject could have been viewed as DSB but that wasn't the specific intent either. You should take some time to more carefully frame your questions. Do you understand that a DSB signal *is* AM? Post your intention; it might help. onto a carrier via a non-linear process), at an envelope detector the two sidebands will be additive. But if you independe ntly place a carrier at frequency ( c ), another carrier at ( c-1 khz) and another carrier at (c+ 1 kHz), the composite can look like an AM signal, but it is not, and only by the most extreme luck will the sidebands be additive at the detector. They would probably cycle between additive and subtractive since they have no real relationship and were not the result of amplitude modulation. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Rich Grise" wrote in message ... Sorry, John - while the ear's amplitude response IS nonlinear, it does not act as a mixer. "Mixing" (multiplication) occurs when a given nonlinear element (in electronics, a diode or transistor, for example) is presented with two signals of different frequencies. But the human ear doesn't work in that manner - there is no single nonlinear element which is receiving more than one signal. Sure there is - the cochlea. (well, the whole middle ear/inner ear system.) Nope - the point had to do with the inner workings of the cochlea. You can't consider it as a single element, as the inner workings consists of what are essentially thousands of very narrowband individual sensors. There is no *single* nonlinear element in which mixing of, say, the hypothetical 300 Hz and 400 Hz tones would take place. John responded that the eardrum (typmanic membrane) would act as such an element, but I would suggest that any mixing which might in theory go on here is not a signifcant factor in how we perceive such tones. The evidence for this is obvious - if presented with, say, a pure 440 Hz "A" from a tuning fork, and the note from the slightly flat instrument we're trying to tune (let's say 438 Hz), we DO hear the 2 Hz "beat" that results from the interference (in the air) between these two sounds. What we do NOT hear to any significant degree is the 878 Hz sum that would be expected if there were much contribution from a multiplicative ("mixing") process. Bob M. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
Jim Kelley wrote:
On Jul 5, 9:38 pm, John Fields wrote: Sure enough, I heard the beat even though it came from different sources, but I couldn't quite get it down to DC even with the scope's trace at 0V. Of course you heard beats. What you didn't hear is the sum of the frequencies. I've had the same setup on my bench for several months. It's also one of the experiments the students do in the first year physics labs. Someone had made the claim a while back that what we hear is the 'average' of the two frequencies. Didn't make any sense so I did the experiment. The results are as I have explained. We hear the average of two frequencies if both frequencies are indistinguishably close, say with a difference of some few hertz. For example, the combination of a 220 Hz signal and a 224 Hz signal with the same amplitude will be perceived as a 4 Hz beat of a 222 Hz tone. gr, Hein |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
Tommy Tootles wrote: Uh, John...respectfully, I have to wonder just who is on drugs. The original poster *ASKED* about *DSB* vs. AM YOU *ANSWERED* about *SSB*. Here is the correct answer... There are two broad types of DSB (double sideband) transmission: DSB-RC and DSB-SC, meaning BOTH sidebands are transmitted, but with either a (R)educed (C)arrier or a (S)urpressed (C)arrier. AM sends both sidebands and full carrier. Hope that answers the OP's question John Smith I wrote: Yeah, you just discovered that for all intents and purposes double sideband is am, and suppressed carrier is just like suppressed carrier am? Oh well, better late than never ... JS What *I* discovered is -not- the point. And for all intents and purposes, "AM" and DSB are two distinct (but certainly related) things. Different hardware to create (balanced modulator for DSB vs high level plate modulation for 'classic' AM), more power required for AM and finally, back in the day, the FCC had -different- emission designators for AM vs DSB. Now, if they were the same, why would you think the FCC gave them -different- emission designators? What IS the point is: 1) The original poster asked a question about "x". 2) You gave a half-assed answer to "y". And then, you had the bare faced gall to accuse the original poster of being on drugs! Look at the good news--even though you gave a partially wrong answer to a question that wasn't even asked, you at least resolved the issue of which of the two of you is on drugs... ;-) |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-lowcarrier frequency
Ron Baker, Pluralitas! wrote:
What is the difference between AM and DSB? The two actually describe different properties, so a signal can be be AM, DSB, neither, or both. And here we run into some trouble between technical correctness and common usage. DSB stands for Double SideBand. Although I suppose an FM signal could be called DSB because it has two *sets* of sidebands, and a narrowband FM signal has only one significant pair like an AM signal, in my experience the term DSB virtually always refers to a signal generated by amplitude modulation. AM is Amplitude Modulation. Straightforward amplitude modulation such as done for AM broadcasting produces a carrier and two sidebands, or DSB with carrier. Either the carrier or one sideband, or both, can be suppressed. If you suppress the carrier (or don't generate it in the first place), you get DSB with suppressed carrier, or DSB-SC. If you suppress one sideband, you get SSB. Usually, but not always, the carrier is also suppressed along with the one sideband, resulting in SSB-SC. NTSC television transmission is VSB -- AM with a carrier and "vestigial" or partially suppressed sideband and a full second sideband. Partial suppression of the carrier is also done for some broadcast purposes. So a commercial AM broadcast station broadcasts a signal that's both AM and DSB. A typical amateur or military SSB transmission is AM but not DSB. A QPSK signal is neither. And, as I mentioned, some signals like FM could be considered DSB but not AM (although this isn't common usage). In common amateur parlance, however, "AM" usually means AM with two sidebands and carrier. "DSB" usually means AM with two sidebands and suppressed carrier "SSB" usually means AM with a single sideband and suppressed carrier Roy Lewallen, W7EL |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... snip After you get done talking about modulation and sidebands, somebody might want to take a stab at explaining why, if you tune a receiver to the second harmonic (or any other harmonic) of a modulated carrier (AM or FM; makes no difference), the audio comes out sounding exactly as it does if you tune to the fundamental? That is, while the second harmonic of the carrier is twice the frequency of the fundamental, the sidebands of the second harmonic are *not* located at twice the frequencies of the sidebands of the fundamental, but rather precisely as far from the second harmonic of the carrier as they are from the fundamental. Isaac Whoa. I thought you were smoking something but my curiosity is piqued. I tried shortwave stations and heard no harmonics. But that could be blamed on propagation. There is an AM station here at 1.21 MHz that is s9+20dB. Tuned to 2.42 MHz. Nothing. Generally the lowest harmonics should be strongest. Then I remembered that many types of non-linearity favor odd harmonics. Tuned to 3.63 MHz. Holy harmonics, batman. There it was and the modulation was not multiplied! Voices sounded normal pitch. When music was played the pitch was the same on the original and the harmonic. One clue is that the effect comes and goes rather abruptly. It seems to switch in and out rather than fade in an out. Maybe the coming and going is from switching the audio material source? This is strange. If a signal is multiplied then the sidebands should be multiplied too. Maybe the carrier generator is generating a harmonic and the harmonic is also being modulated with the normal audio in the modulator. But then that signal would have to make it through the power amp and the antenna. Possible, but why would it come and go? Strange. Hint: Modulation is a "rate effect". Isaac Please elaborate. I am so eager to hear the explanation. The sidebands only show up because there is a rate of change of the carrier -- amplitude or frequency/phase, depending; they aren't separate, stand-alone signals. Since the rate of change of the amplitude of the second harmonic is identical to that of the fundamental, the sidebands show up the same distance away, not twice as distant. Isaac That doesn't explain why the effect would come and go. I don't understand what effect you're referring to here. When I was tuned to the 3rd harmonic sometimes I would hear it and sometimes not. It would come and go rather abruptly. It didn't seem to be gradual fading. But once again you have surprised me. Your explanation of the non-multiplied sidebands, while qualitative and incomplete, is sound. I'm a physicist/engineer, and have been for a long time. I have always The you understand Fourier transforms and convolution. maintained that if the only way one can understand physical phenomena is by solving the differential equations that describe them, then one does not understand the phenomena at all. If you can express a thing in words, such that a person with little mathematical ability can understand what's going on, *then* you have a good grasp of it. I too am a fan of the intuitive approach. But I find that theory is often irreplacable. It looks to me that the tripple frequency sidebands are there but the basic sidebands dominate. Especially at lower modulation indexes. I don't understand what you are saying here either. And in my experience, the term "modulation index" is more likely to show up in a discussion of FM or PM than AM; are you using it interchangeably with "modulation percentage"? http://en.wikipedia.org/wiki/Amplitu...dulation_index Isaac |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
In article ,
Don Bowey wrote: On 7/6/07 12:15 PM, in article , "isw" wrote: In article , Don Bowey wrote: On 7/6/07 9:36 AM, in article , "isw" wrote: In article , Don Bowey wrote: On 7/5/07 10:27 PM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/5/07 12:00 AM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 8:42 PM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 10:16 AM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 7:52 AM, in article , "Ron Baker, Pluralitas!" wrote: snip cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b]) Basically: multiplying two sine waves is the same as adding the (half amplitude) sum and difference frequencies. No, they aren't the same at all, they only appear to be the same before they are examined. The two sidebands will not have the correct phase relationship. What do you mean? What is the "correct" relationship? One could, temporarily, mistake the added combination for a full carrier with independent sidebands, however. (For sines it is sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b]) = 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees]) = 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees]) ) -- rb When AM is correctly accomplished (a single voiceband signal is modulated The questions I posed were not about AM. The subject could have been viewed as DSB but that wasn't the specific intent either. What was the subject of your question? Copying from my original post: Suppose you have a 1 MHz sine wave whose amplitude is multiplied by a 0.1 MHz sine wave. What would it look like on an oscilloscope? What would it look like on a spectrum analyzer? Then suppose you have a 1.1 MHz sine wave added to a 0.9 MHz sine wave. What would that look like on an oscilloscope? What would that look like on a spectrum analyzer? So the first (1) is an AM question and the second (2) is a non-AM question...... What is the difference between AM and DSB? AM is a process. DSB (double sideband), with carrier, is it's most simple result. DSB without carrier (suppressed carrier dsb) requires using, at least, a balanced mixer as the AM multiplier. And requires, for proper reception, that a carrier be recreated at the receiver which has not only the amplitude of the original, There is no need at all to match the carrier amplitude of the original signal. You can use an excessively high carrier injection amplitude with no detrimental affect, but if the injected carrier is too little, the demodulated signal will be over modulated and sound distorted. but also its exact phase. Exact, not required. The closer the better, however. Well, OK, the phase must at least bear a constant relationship to the one that created the signal. If you inject a carrier that has a quadrature relationship to the one that created the DSB signal, the output will be PM (phase modulation). In between zero and 90 degrees, the output is a combination of the two. If the injected carrier is not at precisely the proper frequency, the phase will roll around and the output will be unintelligible. Not unintelligible.... Donald Duckish. I think you are confusing *single* sideband, for which that is correct, and *double* sideband (which we were discussing), for which it is not true. On a more practical side, however, most receiver filters for ssb will essentially remove one sideband if there are two, and can attenuate a carrier so the local product detector can do it's job resulting in improved receiving conditions. But this is more advanced than the Ops questions. Doing it that way will work, but it's not "fair", because you are not actually demodulating a DSB signal (which was the subject of the discussion). Isaac |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
In article ,
Roy Lewallen wrote: Ron Baker, Pluralitas! wrote: What is the difference between AM and DSB? The two actually describe different properties, so a signal can be be AM, DSB, neither, or both. And here we run into some trouble between technical correctness and common usage. DSB stands for Double SideBand. Although I suppose an FM signal could be called DSB because it has two *sets* of sidebands Um, actually, it has a lot more than that. A carrier FM modulated by a single sine wave has an infinite number of sidebands. If the modulating signal is more complex, then things get really complicated. Isaac |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
"isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "John Fields" wrote in message ... On Thu, 5 Jul 2007 00:00:45 -0700, "Ron Baker, Pluralitas!" snip When AM is correctly accomplished (a single voiceband signal is modulated The questions I posed were not about AM. The subject could have been viewed as DSB but that wasn't the specific intent either. What was the subject of your question? Copying from my original post: Suppose you have a 1 MHz sine wave whose amplitude is multiplied by a 0.1 MHz sine wave. What would it look like on an oscilloscope? What would it look like on a spectrum analyzer? Then suppose you have a 1.1 MHz sine wave added to a 0.9 MHz sine wave. What would that look like on an oscilloscope? What would that look like on a spectrum analyzer? --- The first example is amplitude modulation precisely _because_ of the Is there multiplication in DSB? (double sideband) Yes, and in fact, that multiplication referred to above creates a DSB-suppressed-carrier signal. To get "real" AM, you need to add back the carrier *at the proper phase*. So does the multiplication in the first example really make it amplitude modulation? FWIW, if you do the multiplication and then add back a carrier which is in quadrature (90 degrees) to the one you started with, what you get is phase modulation, a "close relative" of FM, and indistinguishable from it for the most part. A true DSB-suppressed carrier signal is rather difficult to receive precisely because of the absolute phase requirement; tuning a receiver to the right frequency isn't sufficient -- the phase has to match, too, and that's really difficult without some sort of reference. A SSB-suppressed carrier signal is a lot simpler to detect because an error in the frequency of the regenerated carrier merely produces a similar error in the frequency of the detected audio (the well-known "Donald Duck" effect). Isaac |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
"Tommy Tootles" wrote in message t... Tommy Tootles wrote: Uh, John...respectfully, I have to wonder just who is on drugs. The original poster *ASKED* about *DSB* vs. AM YOU *ANSWERED* about *SSB*. Here is the correct answer... There are two broad types of DSB (double sideband) transmission: DSB-RC and DSB-SC, meaning BOTH sidebands are transmitted, but with either a (R)educed (C)arrier or a (S)urpressed (C)arrier. AM sends both sidebands and full carrier. Hope that answers the OP's question John Smith I wrote: Yeah, you just discovered that for all intents and purposes double sideband is am, and suppressed carrier is just like suppressed carrier am? Oh well, better late than never ... JS What *I* discovered is -not- the point. And for all intents and purposes, "AM" and DSB are two distinct (but certainly related) things. Different hardware to create (balanced modulator for DSB vs high level plate modulation for 'classic' AM), more power required for AM and finally, back in the day, the FCC had -different- emission designators for AM vs DSB. Now, if they were the same, why would you think the FCC gave them -different- emission designators? You make good, relevant points there. What IS the point is: 1) The original poster asked a question about "x". 2) You gave a half-assed answer to "y". And then, you had the bare faced gall to accuse the original poster of being on drugs! Look at the good news--even though you gave a partially wrong answer to a question that wasn't even asked, you at least resolved the issue of which of the two of you is on drugs... ;-) I would agree with the above also, but don't wish to be provocative. ;) |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
Tommy Tootles wrote:
[chit] Hmmm, why be a half-assed-idiot when you can be a full fledged one? I see your point ... Point is, DSB IS AM, you can receive it on any am receiver, get a life, get off drugs and certainly get off the news groups, you are ill suited to be here ... JS |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: snip While it might not be obvious, the two cases I described are basically identical. And this situation occurs in real life, i.e. in radio signals, oceanography, and guitar tuning. The beat you hear during guitar tuning is not modulation; there is no non-linear process involved (i.e. no multiplication). Isaac In short, the human auditory system is not linear. It has a finite resolution bandwidth. It can't resolve two tones separted by a few Hertz as two separate tones. (But if they are separted by 100 Hz they can easily be separated without hearing a beat.) Two tones 100 Hz apart may or may not be perceived separately; depends on a lot of other factors. MP3 encoding, for example, depends on the ear's (very predictable) inability to discern tones "nearby" to other, louder ones. I'll remember that the next time I'm tuning an MP3 guitar. The same affect can be seen on a spectrum analyzer. Give it two frequencies separated by 1 Hz. Set the resolution bandwidth to 10 Hz. You'll see the peak rise and fall at 1 Hz. Yup. And the spectrum analyzer is (hopefully) a very linear system, producing no intermodulation of its own. Isaac What does a spectrum analyzer use to arive at amplitude values? An envelope detector? Is that linear? I'm sure there's more than one way to do it, but I feel certain that any Which of them is linear? A well-designed filter running into a bolometer would be. You can make the filter narrow enough to respond to only one frequency component at Any real spectrum analyzer has a lower limit to its resolution bandwidth, does it not? The resolution bandwidth of the human ear is non-zero and not really adjustable, is it not? the time, and a bolometer just turns the signal power into heat; nothing nonlinear there... Really? You said you are a physicist/engineer. What does "linear" mean? |
AM electromagnetic waves: 20 KHzmodulationfrequencyonanastronomically-low carrier frequency
On 7/6/07 8:21 PM, in article
, "isw" wrote: In article , Don Bowey wrote: On 7/6/07 12:15 PM, in article , "isw" wrote: In article , Don Bowey wrote: On 7/6/07 9:36 AM, in article , "isw" wrote: In article , Don Bowey wrote: On 7/5/07 10:27 PM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/5/07 12:00 AM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 8:42 PM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 10:16 AM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 7:52 AM, in article , "Ron Baker, Pluralitas!" wrote: snip cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b]) Basically: multiplying two sine waves is the same as adding the (half amplitude) sum and difference frequencies. No, they aren't the same at all, they only appear to be the same before they are examined. The two sidebands will not have the correct phase relationship. What do you mean? What is the "correct" relationship? One could, temporarily, mistake the added combination for a full carrier with independent sidebands, however. (For sines it is sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b]) = 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees]) = 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees]) ) -- rb When AM is correctly accomplished (a single voiceband signal is modulated The questions I posed were not about AM. The subject could have been viewed as DSB but that wasn't the specific intent either. What was the subject of your question? Copying from my original post: Suppose you have a 1 MHz sine wave whose amplitude is multiplied by a 0.1 MHz sine wave. What would it look like on an oscilloscope? What would it look like on a spectrum analyzer? Then suppose you have a 1.1 MHz sine wave added to a 0.9 MHz sine wave. What would that look like on an oscilloscope? What would that look like on a spectrum analyzer? So the first (1) is an AM question and the second (2) is a non-AM question...... What is the difference between AM and DSB? AM is a process. DSB (double sideband), with carrier, is it's most simple result. DSB without carrier (suppressed carrier dsb) requires using, at least, a balanced mixer as the AM multiplier. And requires, for proper reception, that a carrier be recreated at the receiver which has not only the amplitude of the original, There is no need at all to match the carrier amplitude of the original signal. You can use an excessively high carrier injection amplitude with no detrimental affect, but if the injected carrier is too little, the demodulated signal will be over modulated and sound distorted. but also its exact phase. Exact, not required. The closer the better, however. Well, OK, the phase must at least bear a constant relationship to the one that created the signal. If you inject a carrier that has a quadrature relationship to the one that created the DSB signal, the output will be PM (phase modulation). In between zero and 90 degrees, the output is a combination of the two. If the injected carrier is not at precisely the proper frequency, the phase will roll around and the output will be unintelligible. Not unintelligible.... Donald Duckish. I think you are confusing *single* sideband, for which that is correct, and *double* sideband (which we were discussing), for which it is not true. What do you propose the term be for the output of a slightly de-tuned demodulator of a DSB sans carrier, signal? On a more practical side, however, most receiver filters for ssb will essentially remove one sideband if there are two, and can attenuate a carrier so the local product detector can do it's job resulting in improved receiving conditions. But this is more advanced than the Ops questions. Doing it that way will work, but it's not "fair", because you are not actually demodulating a DSB signal (which was the subject of the discussion). I don't believe the OP stated whether the DSB signal was with or without carrier. If without carrier, demodulation is certainly called for. If with carrier, it hardly merits discussion. Isaac |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
On 7/6/07 7:15 PM, in article
, "Tommy Tootles" wrote: Tommy Tootles wrote: Uh, John...respectfully, I have to wonder just who is on drugs. The original poster *ASKED* about *DSB* vs. AM YOU *ANSWERED* about *SSB*. Here is the correct answer... There are two broad types of DSB (double sideband) transmission: DSB-RC and DSB-SC, meaning BOTH sidebands are transmitted, but with either a (R)educed (C)arrier or a (S)urpressed (C)arrier. AM sends both sidebands and full carrier. Hope that answers the OP's question John Smith I wrote: Yeah, you just discovered that for all intents and purposes double sideband is am, and suppressed carrier is just like suppressed carrier am? Oh well, better late than never ... JS What *I* discovered is -not- the point. And for all intents and purposes, "AM" and DSB are two distinct (but certainly related) things Different hardware to create (balanced modulator for DSB vs high level plate modulation for 'classic' AM), more power required for AM and finally, back in the day, the FCC had -different- emission designators for AM vs DSB. Now, if they were the same, why would you think the FCC gave them -different- emission designators? You are confusing FCC use codes and technical processes. Do you believe the FCC Designator of "J" for ssbsc says HOW to do it. Not for an instant. What IS the point is: 1) The original poster asked a question about "x". 2) You gave a half-assed answer to "y". And then, you had the bare faced gall to accuse the original poster of being on drugs! Look at the good news--even though you gave a partially wrong answer to a question that wasn't even asked, you at least resolved the issue of which of the two of you is on drugs... ;-) |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-lowcarrier frequency
isw wrote:
In article , Roy Lewallen wrote: . . . DSB stands for Double SideBand. Although I suppose an FM signal could be called DSB because it has two *sets* of sidebands Um, actually, it has a lot more than that. A carrier FM modulated by a single sine wave has an infinite number of sidebands. If the modulating signal is more complex, then things get really complicated. Sometimes it's difficult to communicate. A "set" can consist of more than one. In the case of FM, each set includes an infinite number, although only a limited number contain a significant amount of energy. The remainder can be ignored without any substantial degradation of received signal quality. This is true regardless of the complexity of the modulating signal. Roy Lewallen, W7EL |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
John 'Half-way' Smith I wrote:
Point is, DSB IS AM, you can receive it on any am receiver, Well, another of your half-assed answers. You can receive *DSB-RC* on any AM receiver because the carrier, although reduced, allows reception via a simple envelope detector. On the other hand, DSB-SC requires a product detector, a coherent detector or a Costas Loop, detectors NOT available on "any" AM receiver. So, yet another "half-an-answer" on your part. get off drugs and certainly get off the news groups, you are ill suited to be here ... A person asks about "a", *you* give them an answer to "b", then accuse -them- of being on drugs and say -they- are ill-suited to be here. May I suggest that you look in the mirror if you are concerned about suitability... Your thought processes and (lack of) logic seem quite odd. Odd enough to question who the drug user might be. |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
Tommy Tootles wrote:
What *I* discovered is -not- the point. And for all intents and purposes, "AM" and DSB are two distinct (but certainly related) things Different hardware to create (balanced modulator for DSB vs high level plate modulation for 'classic' AM), more power required for AM and finally, back in the day, the FCC had -different- emission designators for AM vs DSB. Now, if they were the same, why would you think the FCC gave them -different- emission designators? Don Bowey wrote: You are confusing FCC use codes and technical processes. Do you believe the FCC Designator of "J" for ssbsc says HOW to do it. Not for an instant. Don, I believe you are misinterpreting or misunderstanding what I wrote--and my apologies if I wasn't clear enough in my statement above. Let me clarify... I was NOT confusing FCC use codes and technical processes. I made two separate, *stand-alone* statements: Statement 1 ( technical processes)--low level balanced modulator vs.high level plate modulation. A true statement. Statement 2 ( FCC emission designators)-- that the FCC had different emission designators for AM, DSB-SC and DSB-RC *BACK IN THE DAY*. A true statement. By "back in the day", I was referring to the late 50s and early 60s when sideband (of all varieties) was just coming in to usage in the ham radio world. Everything was so new that SSB hadn't yet emerged as the mode of choice. Some rigs back then were capable of both SSB and the two flavors of DSB. The FCC (AT THAT TIME--"back in the day") had designators for all of the above. The FCC emission designators have changed at least once (and maybe more) since those days. In any event, they were meant to be two stand-alone statements, with -no- implication intended that the designator tells how to do it. So, either you need to read more carefully, I need to write more carefully or all of the above... :-) |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
In article ,
Don Bowey wrote: --bunch of stuff trimmed off-- Well, OK, the phase must at least bear a constant relationship to the one that created the signal. If you inject a carrier that has a quadrature relationship to the one that created the DSB signal, the output will be PM (phase modulation). In between zero and 90 degrees, the output is a combination of the two. If the injected carrier is not at precisely the proper frequency, the phase will roll around and the output will be unintelligible. Not unintelligible.... Donald Duckish. I think you are confusing *single* sideband, for which that is correct, and *double* sideband (which we were discussing), for which it is not true. What do you propose the term be for the output of a slightly de-tuned demodulator of a DSB sans carrier, signal? I'm not sure it has a name. The output is constantly swishing around between AM and PM, at a rate determined by the frequency error of the reinjected carrier. Most detectors will have a problem with it. Isaac |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
In article ,
"Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: snip While it might not be obvious, the two cases I described are basically identical. And this situation occurs in real life, i.e. in radio signals, oceanography, and guitar tuning. The beat you hear during guitar tuning is not modulation; there is no non-linear process involved (i.e. no multiplication). Isaac In short, the human auditory system is not linear. It has a finite resolution bandwidth. It can't resolve two tones separted by a few Hertz as two separate tones. (But if they are separted by 100 Hz they can easily be separated without hearing a beat.) Two tones 100 Hz apart may or may not be perceived separately; depends on a lot of other factors. MP3 encoding, for example, depends on the ear's (very predictable) inability to discern tones "nearby" to other, louder ones. I'll remember that the next time I'm tuning an MP3 guitar. The same affect can be seen on a spectrum analyzer. Give it two frequencies separated by 1 Hz. Set the resolution bandwidth to 10 Hz. You'll see the peak rise and fall at 1 Hz. Yup. And the spectrum analyzer is (hopefully) a very linear system, producing no intermodulation of its own. Isaac What does a spectrum analyzer use to arive at amplitude values? An envelope detector? Is that linear? I'm sure there's more than one way to do it, but I feel certain that any Which of them is linear? A well-designed filter running into a bolometer would be. You can make the filter narrow enough to respond to only one frequency component at Any real spectrum analyzer has a lower limit to its resolution bandwidth, does it not? The resolution bandwidth of the human ear is non-zero and not really adjustable, is it not? the time, and a bolometer just turns the signal power into heat; nothing nonlinear there... Really? You said you are a physicist/engineer. What does "linear" mean? Let's not get too far off the subject here. We were discussing whether the "tuning beat" that you use to tune a musical instrument involved a nonlinear process (ie. "modulation"). I said that it does not, and that it could be detected by instrumentation which was proveably linear (i.e. not "perfectly" linear, because that's not required, but certainly linear enough to discount the requirement for "modulation"). That's all. Isaac |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
In article ,
"Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "John Fields" wrote in message ... On Thu, 5 Jul 2007 00:00:45 -0700, "Ron Baker, Pluralitas!" snip When AM is correctly accomplished (a single voiceband signal is modulated The questions I posed were not about AM. The subject could have been viewed as DSB but that wasn't the specific intent either. What was the subject of your question? Copying from my original post: Suppose you have a 1 MHz sine wave whose amplitude is multiplied by a 0.1 MHz sine wave. What would it look like on an oscilloscope? What would it look like on a spectrum analyzer? Then suppose you have a 1.1 MHz sine wave added to a 0.9 MHz sine wave. What would that look like on an oscilloscope? What would that look like on a spectrum analyzer? --- The first example is amplitude modulation precisely _because_ of the Is there multiplication in DSB? (double sideband) Yes, and in fact, that multiplication referred to above creates a DSB-suppressed-carrier signal. To get "real" AM, you need to add back the carrier *at the proper phase*. So does the multiplication in the first example really make it amplitude modulation? Yes, because the output signal varies in amplitude with modulation. For suppressed carrier SSB or DSB, the output is zero when there's no modulating signal, while for "traditional AM", the output is 50% for no modulation. Compare to FM or PM, where the output is constant regardless of the modulation level. True, FM has a lot of sidebands that vary in amplitude, but if you add them all together, the output is constant. Run an SSB, DSB, or AM rig into a dummy load and it'll get hotter with modulation, while with FM the temperature won't change. -- But recall that if you take that DSB signal you got by multiplication, and reinject the carrier in quadrature, you no longer have amplitude modulation. Isaac |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: "isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: snip While it might not be obvious, the two cases I described are basically identical. And this situation occurs in real life, i.e. in radio signals, oceanography, and guitar tuning. The beat you hear during guitar tuning is not modulation; there is no non-linear process involved (i.e. no multiplication). Isaac In short, the human auditory system is not linear. It has a finite resolution bandwidth. It can't resolve two tones separted by a few Hertz as two separate tones. (But if they are separted by 100 Hz they can easily be separated without hearing a beat.) Two tones 100 Hz apart may or may not be perceived separately; depends on a lot of other factors. MP3 encoding, for example, depends on the ear's (very predictable) inability to discern tones "nearby" to other, louder ones. I'll remember that the next time I'm tuning an MP3 guitar. The same affect can be seen on a spectrum analyzer. Give it two frequencies separated by 1 Hz. Set the resolution bandwidth to 10 Hz. You'll see the peak rise and fall at 1 Hz. Yup. And the spectrum analyzer is (hopefully) a very linear system, producing no intermodulation of its own. Isaac What does a spectrum analyzer use to arive at amplitude values? An envelope detector? Is that linear? I'm sure there's more than one way to do it, but I feel certain that any Which of them is linear? A well-designed filter running into a bolometer would be. You can make the filter narrow enough to respond to only one frequency component at Any real spectrum analyzer has a lower limit to its resolution bandwidth, does it not? The resolution bandwidth of the human ear is non-zero and not really adjustable, is it not? the time, and a bolometer just turns the signal power into heat; nothing nonlinear there... Really? You said you are a physicist/engineer. What does "linear" mean? Let's not get too far off the subject here. We were discussing whether the "tuning beat" that you use to tune a musical instrument involved a nonlinear process (ie. "modulation"). Then linearity is at the core of the matter. What does "linear" (or "nonlinear") mean to you? I said that it does not, and that it could be detected by instrumentation which was proveably linear (i.e. not "perfectly" linear, because that's not required, but certainly linear enough to discount the requirement for "modulation"). No nonlinearity is necessary in order to hear a beat? Where does the beat come from? That's all. Isaac |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Ron Baker, Pluralitas!" wrote in message ... First of all, do you think you could possibly learn to trim your posts? No nonlinearity is necessary in order to hear a beat? Where does the beat come from? An audible beat tone is produced by the constructive and destructive interference between two sound waves in air. Look at a pictorial representation (in the time domain) of the sum of sine waves,of similar amplitudes, one at, say, 1000 Hz and the other at 1005, and you'll see it. Bob M. |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
Tommy Tootles wrote:
[stuff] Your expansion of the original and simple question into a convoluted and obfuscated mess shows an outstanding knack for skills related to the psychotic ... however, it also shows you to be an idiot. Hey, are you attempting to fake a mental disorder so you can get off welfare and onto SSI? Sharpen your razor blade, return to the mental hospital--begin splitting hairs ... JS |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
On Jul 7, 12:44 pm, John Smith I wrote:
Tommy Tootles wrote: [stuff] Your expansion of the original and simple question into a convoluted and obfuscated mess shows an outstanding knack for skills related to the psychotic ... however, it also shows you to be an idiot. Hey, are you attempting to fake a mental disorder so you can get off welfare and onto SSI? Sharpen your razor blade, return to the mental hospital--begin splitting hairs ... JS Ah the War-of-the-Words continues ~ RHF |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
In article ,
"Ron Baker, Pluralitas!" wrote: --snippage-- That doesn't explain why the effect would come and go. I don't understand what effect you're referring to here. When I was tuned to the 3rd harmonic sometimes I would hear it and sometimes not. It would come and go rather abruptly. It didn't seem to be gradual fading. Especially if the RF field is strong, there are a lot of mechanisms which can create harmonics after the signal leaves the transmitter -- rusty fencing, or tooth fillings, for example. I can see how one of those could be intermittent. But once again you have surprised me. Your explanation of the non-multiplied sidebands, while qualitative and incomplete, is sound. I'm a physicist/engineer, and have been for a long time. I have always The you understand Fourier transforms and convolution. I suppose so; I've spent over fifteen years poking around in the entrails of MPEG... I don't understand what you are saying here either. And in my experience, the term "modulation index" is more likely to show up in a discussion of FM or PM than AM; are you using it interchangeably with "modulation percentage"? As I suspected -- just different words for the same thing. So: It looks to me that the tripple frequency sidebands are there but the basic sidebands dominate. Especially at lower modulation indexes. With well-designed gear (or theoretically), for AM there will be no other frequencies present except for the carrier and the ones represented by the Fourier spectrum of the modulation -- one set either side of the carrier. That is only true, of course, as long as there is no overmodulation; that creates a *lot* of other junk, because there are periods where the carrier is entirely cut off. So I still don't understand what you mean by "triple frequency sidebands" or "basic sidebands". As I said in another post, modulation is a "rate effect", so there never should be any frequencies generated at multiples of the sidebands surrounding the fundamental; instead they are always identically as far from the harmonics as they are from the fundamental. Is that what you are calling "triple frequency sidebands"? Isaac |
What Was "Radium's" Original Question ? -and- Has It Been Answered ? AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
On Jun 29, 7:41 pm, Radium wrote:
Hi: Please don't be annoyed/offended by my question as I decreased the modulation frequency to where it would actually be realistic. I have a very weird question about electromagnetic radiation, carriers, and modulators. Is it mathematically-possible to carry a modulator signal [in this case, a pure-sine-wave-tone] with a frequency of 20 KHz and an amplitude of 1-watt-per-meter-squared on a AM carrier signal whose frequency is 10^-(1,000,000,000-to-the-power-10^1,000,000,000) nanocycle* every 10^1,000,000,000-to-the-power-10^1,000,000,000 giga- eons and whose amplitude is a minimum of 10^1,000,000,000-to-the- power-10^1,000,000,000 gigaphotons per 10^-(1,000,000,000-to-the- power-10^1,000,000,000) nanosecond? If it is not mathematically-possible, then please explain why. 10^-(1,000,000,000-to-the-power-10^1,000,000,000) second is an extremely short amount of time. 10^-(1,000,000,000-to-the- power-10^1,000,000,000) nanosecond is even shorter because a nanosecond is shorter than a second. Giga-eon = a billion eons Eon = a billion years *nanocycle = billionth of a cycle Gigaphoton = a billion photons 10^1,000,000,000-to-the-power-10^1,000,000,000 -- now that is one large large number. 10^1,000,000,000 = 10-to-the-power-1,000,000,000 So you get: (10-to-the-power-1,000,000,000) to the power (10-to-the- power-1,000,000,000) 10^-(1,000,000,000-to-the-power-10^1,000,000,000) = 10^-(10-to-the- power-1,000,000,000)-to-the-power-(10-to-the-power-1,000,000,000) 10^-(10-to-the-power-1,000,000,000) to the power (10-to-the- power-1,000,000,000) is an extremely small number at it equals 10-to- the-power-NEGATIVE-[(10-to-the-power-1,000,000,000) to the power (10- to-the-power-1,000,000,000)] No offense but please respond with reasonable answers & keep out the jokes, off-topic nonsense, taunts, insults, and trivializations. I am really interested in this. Thanks, Radium WHAT WAS "RADIUM'S" ORIGINAL QUESTION ? -and- HAS IT BEEN ANSWERED ? Hi: Please don't be annoyed/offended by my question as I decreased the modulation frequency to where it would actually be realistic. I have a very weird question about electromagnetic radiation, carriers, and modulators. Is it mathematically-possible to carry a modulator signal [in this case, a pure-sine-wave-tone] with a frequency of 20 KHz and an amplitude of 1-watt-per-meter-squared on a AM carrier signal whose frequency is 10^-(1,000,000,000-to-the-power-10^1,000,000,000) nanocycle* every 10^1,000,000,000-to-the-power-10^1,000,000,000 giga- eons and whose amplitude is a minimum of 10^1,000,000,000-to-the- power-10^1,000,000,000 gigaphotons per 10^-(1,000,000,000-to-the- power-10^1,000,000,000) nanosecond? If it is not mathematically-possible, then please explain why. 10^-(1,000,000,000-to-the-power-10^1,000,000,000) second is an extremely short amount of time. 10^-(1,000,000,000-to-the- power-10^1,000,000,000) nanosecond is even shorter because a nanosecond is shorter than a second. Giga-eon = a billion eons Eon = a billion years *nanocycle = billionth of a cycle Gigaphoton = a billion photons 10^1,000,000,000-to-the-power-10^1,000,000,000 -- now that is one large large number. 10^1,000,000,000 = 10-to-the-power-1,000,000,000 So you get: (10-to-the-power-1,000,000,000) to the power (10-to-the- power-1,000,000,000) 10^-(1,000,000,000-to-the-power-10^1,000,000,000) = 10^-(10-to-the- power-1,000,000,000)-to-the-power-(10-to-the-power-1,000,000,000) 10^-(10-to-the-power-1,000,000,000) to the power (10-to-the- power-1,000,000,000) is an extremely small number at it equals 10-to- the-power-NEGATIVE-[(10-to-the-power-1,000,000,000) to the power (10- to-the-power-1,000,000,000)] No offense but please respond with reasonable answers & keep out the jokes, off-topic nonsense, taunts, insults, and trivializations. I am really interested in this. Thanks, Radium |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Bob Myers" wrote in message ... "Ron Baker, Pluralitas!" wrote in message ... First of all, do you think you could possibly learn to trim your posts? No nonlinearity is necessary in order to hear a beat? Where does the beat come from? An audible beat tone is produced by the constructive and destructive interference between two sound waves in air. Look at a pictorial representation (in the time domain) of the sum of sine waves,of similar amplitudes, one at, say, 1000 Hz and the other at 1005, and you'll see it. Bob M. How come you don't hear a 200 Hz beat with a 1000 Hz tone and a 1200 Hz tone? |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Bob Myers" wrote in message ... "Ron Baker, Pluralitas!" wrote in message ... "Bob Myers" wrote in message ... "Ron Baker, Pluralitas!" wrote in message ... First of all, do you think you could possibly learn to trim your posts? Apparently, no, you can't. Too lazy to take the trouble to perform this common courtesy, or what? You could always plonk me. An audible beat tone is produced by the constructive and destructive interference between two sound waves in air. Look at a pictorial representation (in the time domain) of the sum of sine waves,of similar amplitudes, one at, say, 1000 Hz and the other at 1005, and you'll see it. Bob M. How come you don't hear a 200 Hz beat with a 1000 Hz tone and a 1200 Hz tone? For the simple reason that there isn't actually a "tone" involved - in other words, there is no actual signal at the difference frequency. There can't be, since there is no "mixing" (multiplication) of the two original tones. There is no multiplication of 1000 Hz and 1005 Hz either, is there? Why don't you hear 1000 Hz and 1005 Hz rather than a single tone varying in amplitude? The "beat" is really just the perception of the amplitude variation caused by the interference previously mentioned. You cannot sense such variations if they occur rapidly enough, any more than you can detect the flicker of a light source which is varying rapidly enough. Bob M. Could it be that the human auditory system is not linear? |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
"Don Bowey" wrote in message ... On 7/4/07 8:42 PM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 10:16 AM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 7:52 AM, in article , "Ron Baker, Pluralitas!" wrote: snip cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b]) Basically: multiplying two sine waves is the same as adding the (half amplitude) sum and difference frequencies. No, they aren't the same at all, they only appear to be the same before they are examined. The two sidebands will not have the correct phase relationship. What do you mean? What is the "correct" relationship? One could, temporarily, mistake the added combination for a full carrier with independent sidebands, however. (For sines it is sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b]) = 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees]) = 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees]) ) -- rb When AM is correctly accomplished (a single voiceband signal is modulated The questions I posed were not about AM. The subject could have been viewed as DSB but that wasn't the specific intent either. You should take some time to more carefully frame your questions. Do you understand that a DSB signal *is* AM? So all the AM broadcasters are wasting money by generating a carrier? Post your intention; it might help. onto a carrier via a non-linear process), at an envelope detector the two sidebands will be additive. But if you independe ntly place a carrier at frequency ( c ), another carrier at ( c-1 khz) and another carrier at (c+ 1 kHz), the composite can look like an AM signal, but it is not, and only by the most extreme luck will the sidebands be additive at the detector. They would probably cycle between additive and subtractive since they have no real relationship and were not the result of amplitude modulation. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Rich Grise" wrote in message ... On Tue, 03 Jul 2007 22:42:20 -0700, isw wrote: After you get done talking about modulation and sidebands, somebody might want to take a stab at explaining why, if you tune a receiver to the second harmonic (or any other harmonic) of a modulated carrier (AM or FM; makes no difference), the audio comes out sounding exactly as it does if you tune to the fundamental? That is, while the second harmonic of the carrier is twice the frequency of the fundamental, the sidebands of the second harmonic are *not* located at twice the frequencies of the sidebands of the fundamental, but rather precisely as far from the second harmonic of the carrier as they are from the fundamental. Have you ever actually observed this effect? Thanks, Rich I have. I tuned to the third harmonic of a strong local AM broadcast station. There it was. Quite a surprise. It is a bit distorted but intelligible. Another odd thing is that it comes and goes somewhat abruptly. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
In article ,
"Ron Baker, Pluralitas!" wrote: --snippety-snip-- You said you are a physicist/engineer. What does "linear" mean? Let's not get too far off the subject here. We were discussing whether the "tuning beat" that you use to tune a musical instrument involved a nonlinear process (ie. "modulation"). Then linearity is at the core of the matter. What does "linear" (or "nonlinear") mean to you? OK, if you insist -- *in this case* it means "linear enough to not produce IM products of significant amplitude". I said that it does not, and that it could be detected by instrumentation which was proveably linear (i.e. not "perfectly" linear, because that's not required, but certainly linear enough to discount the requirement for "modulation"). No nonlinearity is necessary in order to hear a beat? Where does the beat come from? As the phase of the two nearly equal waves move past each other, there is simple vector summation which varies the amplitude. Consider two sine waves of precisely the same frequency, where one of them is adjustable in phase -- use a goniometer, for instance. Use a set of resistors to sum the two signals, and observe the summing point with a 'scope or a loudspeaker. By altering the phase of one source, you can get any amplitude you want from zero up to twice the amplitude of either one. Now just twiddle that phase knob around and around as fast as you can. You've just slightly altered the instantaneous frequency of one of the generators (but only while you twiddle), and accomplished pretty much the same effect as listening to the beat between two guitar strings at nearly zero frequency offset. With no nonlinear processes in sight. Isaac |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
On 7/7/07 9:17 PM, in article , "Ron
Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 8:42 PM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 10:16 AM, in article , "Ron Baker, Pluralitas!" wrote: "Don Bowey" wrote in message ... On 7/4/07 7:52 AM, in article , "Ron Baker, Pluralitas!" wrote: snip cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b]) Basically: multiplying two sine waves is the same as adding the (half amplitude) sum and difference frequencies. No, they aren't the same at all, they only appear to be the same before they are examined. The two sidebands will not have the correct phase relationship. What do you mean? What is the "correct" relationship? One could, temporarily, mistake the added combination for a full carrier with independent sidebands, however. (For sines it is sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b]) = 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees]) = 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees]) ) -- rb When AM is correctly accomplished (a single voiceband signal is modulated The questions I posed were not about AM. The subject could have been viewed as DSB but that wasn't the specific intent either. You should take some time to more carefully frame your questions. Do you understand that a DSB signal *is* AM? So all the AM broadcasters are wasting money by generating a carrier? You are an ignorant, useless troll, and not worth my time Post your intention; it might help. onto a carrier via a non-linear process), at an envelope detector the two sidebands will be additive. But if you independe ntly place a carrier at frequency ( c ), another carrier at ( c-1 khz) and another carrier at (c+ 1 kHz), the composite can look like an AM signal, but it is not, and only by the most extreme luck will the sidebands be additive at the detector. They would probably cycle between additive and subtractive since they have no real relationship and were not the result of amplitude modulation. |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
"Ron Baker, Pluralitas!" wrote in message ... Do you understand that a DSB signal *is* AM? So all the AM broadcasters are wasting money by generating a carrier? How did you jump to that conclusion. |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
Ron Baker, Pluralitas! wrote:
Could it be that the human auditory system is not linear? No. Humans had to evolve to incorporate a non linear response to sound when the electronics manufacturers started supplying ONLY non linear potentiometers for audio equipment use. This mutation, which is now the norm, was completely unknown before the start of the twentieth century. We, here at Densa Labs, call it Darwinian Decibelism mike |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
On Jul 7, 9:56 pm, "Dana" wrote:
"Ron Baker, Pluralitas!" wrote in om... Do you understand that a DSB signal *is* AM? - - - So all the AM broadcasters are wasting money by - - generating a carrier? - - How did you jump to that conclusion. Somewhere between the Original Post #1 and the 236 Replies to date. ~ RHF |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"isw" wrote in message ... In article , "Ron Baker, Pluralitas!" wrote: --snippety-snip-- You said you are a physicist/engineer. What does "linear" mean? Let's not get too far off the subject here. We were discussing whether the "tuning beat" that you use to tune a musical instrument involved a nonlinear process (ie. "modulation"). Then linearity is at the core of the matter. What does "linear" (or "nonlinear") mean to you? OK, if you insist -- *in this case* it means "linear enough to not produce IM products of significant amplitude". Good enough. Then spectrum analyzers and the human auditory system are not linear. Stay with me here. I said that it does not, and that it could be detected by instrumentation which was proveably linear (i.e. not "perfectly" linear, because that's not required, but certainly linear enough to discount the requirement for "modulation"). No nonlinearity is necessary in order to hear a beat? Where does the beat come from? As the phase of the two nearly equal waves move past each other, there is simple vector summation which varies the amplitude. Consider two sine waves of precisely the same frequency, where one of them is adjustable in phase -- use a goniometer, for instance. Use a set of resistors to sum the two signals, and observe the summing point with a 'scope or a loudspeaker. By altering the phase of one source, you can get any amplitude you want from zero up to twice the amplitude of either one. Now just twiddle that phase knob around and around as fast as you can. You've just slightly altered the instantaneous frequency of one of the generators (but only while you twiddle), and accomplished pretty much the same effect as listening to the beat between two guitar strings at nearly zero frequency offset. With no nonlinear processes in sight. Isaac You put some effort into that. I give you credit for that. The socratic thing isn't working, so here you go. Is an envelope detector linear? The answer is no. But how can that be? If you put in a sine wave of amplitude A you get A volts out (assuming its gain is 1). If you put in a sine wave of amplitude 2A and you get 2A volts out. Linear, right? Now you put in a sine wave of amplitude A at 455 kHz plus a sine wave of amplitude A at 456 kHz. (Consider the envelope detector of a typical AM radio here.) What do you get out? A sine wave of amplitude A/2 at 1 kHz. Intermodulation. An envelope detector is not linear. No envelope/ amplitude detector is linear. The typical envelope detector is a diode rectifier followed by a lowpass filter. The diode rectifier is obviously nonlinear and gives you all sorts of intermoduation. With a single sine wave input you get a DC term and various harmonics of the sine wave. The lowpass filter filters out all the harmonics and leaves the DC. If you put in two sine waves (assuming their frequencies are above the cutoff of the subsequent lowpass and their difference is within the lowpass) again the diode nonlinearity results in intermodulation. You get a DC component, the difference frequency, the sum, and various higher frequencies. The filter leaves only the difference frequency and the DC. In an AM receiver the DC is subsequently blocked too. Do you see how this applies to spectrum analyzers and the human auditory system? |
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