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AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
"John Smith I" wrote in message ... Ron Baker, Pluralitas! wrote: ... 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? Lots of BS here ... The signal ends up looking like a 1Mhz signal contained within the walls of the .1Mhz signal ... and simply said, the 1Mhz signal is enclosed in the envelope of a .1Mhz signal--the "walls" of this .1Mhz signal being referred to as "sidebands." Is that for both cases? Where did the 1 MHz component in your result come from? |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
Ron Baker, Pluralitas! wrote:
Where did the 1 MHz component in your result come from? From your original question; hell to get old and experience Alzheimers', huh? What, you have never seen rf in a modulation envelope before? JS |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
Ron Baker, Pluralitas! wrote:
Where did the 1 MHz component in your result come from? From your original question; hell to get old and experience Alzheimers', huh? What, you have never seen rf in a modulation envelope before? JS |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
"John Smith I" wrote in message ... Ron Baker, Pluralitas! wrote: Where did the 1 MHz component in your result come from? From your original question; hell to get old and experience Alzheimers', huh? Says the fellow who hit the send button twice. :) What, you have never seen rf in a modulation envelope before? JS What is the difference between AM and DSB? |
AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
In message , isw
writes In article , Rich Grise wrote: 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? Sure. (In a previous life, I designed AM and FM transmitters for RCA). Just get a short-wave radio, locate yourself fairly close to a standard AM transmitter, and tune to the harmonics. you'll find, in every case, that the audio sounds just the same as if you were listening to the fundamental. Works for FM, too, but the situation is somewhat more complex. Isaac Yes, I think I'm missing something obvious here. Let me have another think (aloud).... If you FM modulate a 1MHz carrier with a 1kHz tone, you get a spectrum consisting of a 1MHz carrier in the middle, plus a family of sidebands harmonically spaced at 1kHz, 2kHz, 3kHz etc (to infinity). [One obvious difference between the FM spectrum and that of an AM signal is that the AM spectrum only has sidebands at 1kHz, and the amplitude of the carrier does not vary with modulation depth. With the FM signal, the amplitudes of the carrier and each pair of sideband do vary with the amount of modulation.] So, if you FM modulate a 1MHz carrier with a 1kHz tone, you get a 1Mhz carrier and the family of 1kHz 'harmonic' sidebands. Demodulated it, and you hear a 1kHz tone. Now double the signal to 2MHz. You might expect the sidebands to appear at 2, 4, 6kHz etc. However, if you demodulated the signal, you still hear the original 1kHz tone (which should now be double the amplitude of the original 1MHz signal). You definitely don't hear 2kHz. This at least proves that the original 1kHz FM modulation is preserved during the doubling process. So, would it be simplistically correct to consider that, during the doubling process, the original family of 1kHz sidebands also mix with the new 2MHz carrier, and create a family of 1kHz sidebands centred on 2MHz? Or, alternatively, does the original family of 1kHz sidebands (on the 1MHz signal) mix with the original 1MHz carrier to produce a family of baseband 1kHz 'harmonic' signals, and these then mix with the new 2MHz carrier to create the family of 1kHz sidebands centred on 2MHz? Or are both equally valid (invalid)? A possible flaw in my simplistic 'explanations' is that I would have thought that, while the doubling process occurs as a result of 2nd-order intermodulation, surely the two-step process in both 'explanations' is really 4th-order intermodulation? However, my explanations work equally well (?) for FM and AM. Am I wrong, or am I wrong? Ian. -- |
AM electromagnetic waves: 20 KHzmodulationfrequencyonanastronomically-low carrier frequency
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. |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
On 7/5/07 11:51 PM, in article , "Ron
Baker, Pluralitas!" wrote: (snip) What is the difference between AM and DSB? You asked this identical question in another post, and it was answered. |
AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
Ron Baker, Pluralitas! wrote:
... What is the difference between AM and DSB? This is your last question of 1001 questions: Since the information (modulation/voice) is repeated in both sides of the modulation envelope in am, ssb "chops off" one half of the envelope. The receiver is responsible for "mirroring" the other and reproducing the information on that end--this allows for almost doubling the effective range of am. Get off the drugs, get a job and become a productive citizen! JS |
AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
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, but also its exact phase. Absent some sort of "pilot" to get things synchronized, this makes reception very difficult. Isaac |
AM electromagnetic waves: 20 KHzmodulationfrequencyonanastronomically-low carrier frequency
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