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#191
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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? |
#192
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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? |
#193
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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. |
#194
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AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
"Rich Grise" wrote in message news 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. |
#195
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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 |
#196
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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. |
#197
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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. |
#198
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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 |
#199
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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 |
#200
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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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