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George Dishman says Karl Uppiano is wrong about AM radio, carrier-frequencies, and aliasing. Who should I believe? Why?
In article ,
wrote: search for AM modulation You don't need to write "AM modulation", since "AM" means "amplitude modulation". Therefore "AM modulation" becomes "amplitude modulation modulation" ...... :-) But perhaps you were considering adding some subcarrier to the AM? :-))))))))) -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
George Dishman says Karl Uppiano is wrong about AM radio, carrier-frequencies, and aliasing. Who should I believe? Why?
"Paul Schlyter" wrote in message ... : In article , : wrote: : : search for AM modulation : : You don't need to write "AM modulation", since "AM" means : "amplitude modulation". Therefore "AM modulation" becomes : "amplitude modulation modulation" ...... :-) : : But perhaps you were considering adding some subcarrier to the AM? :-))))))))) Alabama is a US state. :-) |
George Dishman says Karl Uppiano is wrong about AM radio, carrier-frequencies, and aliasing. Who should I believe? Why?
In rec.radio.amateur.antenna Paul Schlyter wrote:
In article , wrote: search for AM modulation You don't need to write "AM modulation", since "AM" means "amplitude modulation". Therefore "AM modulation" becomes "amplitude modulation modulation" ...... :-) But perhaps you were considering adding some subcarrier to the AM? :-))))))))) No, I was considering the fact that "am" is a common english word and adding "modulation" to the search disambiguates the search. Google AM: 1,680,000,000 hits starting with "I Am Bored - Sites for when you're bored." Google AM modulation 16,200,000 hits Google AM modulation equation 1,940,000 hits It's called narrowing the search. Or didn't you bother to read the part about "done a Google for" before you started spouting? -- Jim Pennino Remove .spam.sux to reply. |
George Dishman says Karl Uppiano is wrong about AM radio, carrier-frequencies, and aliasing. Who should I believe? Why?
On Jul 14, 10:57 pm, Radium wrote:
George Dishman says Karl Uppiano is wrong about AM radio, carrier- frequencies, and aliasing. Who should I believe and why? On Jul 14, 4:11 pm, "George Dishman" wrote inhttp://groups.google.com/group/sci.astro.amateur/msg/1d3b52bbf05843c0... : "Radium" wrote in message roups.com... On Jul 14, 1:17 am, "George Dishman" wrote: "Radium" wrote in message groups.com... .. Isn't it true that the carrier-frequency must be at least 2x the highest intended frequency of the modulator signal? No. Karl Uppiano sharply disagrees. Karl Uppiano explained in http://groups.google.com/group/sci.e...cea47a5?hl=en& He is wrong. The basis of AM is that the sine wave carrier is multiplied by another signal which can be treated as a sum of sines. The relevant maths is: http://www.sosmath.com/trig/prodform/prodform.html If the carrier frequency if fc and the modulation has frequencies up to fm then you get sidebands like this: http://en.wikipedia.org/wiki/Image:Am-sidebands.png If you multiply 44.1kHz by a band from 20Hz to 20kHz, you get an upper sideband given 44.12kHz to 64.1kHz and a lower sideband from 44.08kHz down to 24.1kHz The highest modulating frequency for AM must be less than 1/2 the carrier frequency. Conversely, the lowest carrier frequency must be twice the highest modulating frequency. Period. I don't care what specific frequencies and/or energies and/or colors you propose. If you want to modulate at 20KHz, the carrier must be at least 40KHz. It is no coincidence that CD audio uses a 44.1KHz sample rate. It is essentially the same principle. If you exceed the Nyquist criterion, the sidebands overlap the baseband (i.e., aliasing occurs) and you cannot unambiguously decode the original modulation. Nyquist applies to sampling. So who is right and who is wrong? Look at the maths, it is never wrong. Modulating fc with fm gives a lowest frequency of fc-fm so as long as fc fm, you don't get aliasing. George So is it possible for me to receive a 10 KHz audio sine-wave tone on a 1 Hz AM radio receiver? If not, why? My guess is it violates Nyquist/ Shannon. Right?- Hide quoted text - - Show quoted text - Depends on what you mean by a "10 KHz audio sine-wave", a "1 Hz AM radio", and on what you mean by "receive". |
George Dishman says Karl Uppiano is wrong about AM radio, carrier-frequencies,and aliasing. Who should I believe? Why?
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George Dishman says Karl Uppiano is wrong about AM radio, carrier-frequencies, and aliasing. Who should I believe? Why?
wrote ...
Depends on what you mean by a "10 KHz audio sine-wave", a "1 Hz AM radio", and on what you mean by "receive". He doesn't mean *anything* by them. He is a troll. He apparently threads technical terms together with some sort of random-phrase generator and gullible people fall for it. |
George Dishman says Karl Uppiano is wrong about AM radio, carrier-frequencies, and aliasing. Who should I believe? Why?
On Jul 15, 3:57 am, Radium wrote:
George Dishman says Karl Uppiano is wrong about AM radio, carrier- frequencies, and aliasing. Who should I believe and why? On Jul 14, 4:11 pm, "George Dishman" wrote inhttp://groups.google.com/group/sci.astro.amateur/msg/1d3b52bbf05843c0... : "Radium" wrote in message roups.com... On Jul 14, 1:17 am, "George Dishman" wrote: "Radium" wrote in message groups.com... .. Isn't it true that the carrier-frequency must be at least 2x the highest intended frequency of the modulator signal? No. Karl Uppiano sharply disagrees. Karl Uppiano explained in http://groups.google.com/group/sci.e...cea47a5?hl=en& He is wrong. The basis of AM is that the sine wave carrier is multiplied by another signal which can be treated as a sum of sines. The relevant maths is: http://www.sosmath.com/trig/prodform/prodform.html If the carrier frequency if fc and the modulation has frequencies up to fm then you get sidebands like this: http://en.wikipedia.org/wiki/Image:Am-sidebands.png If you multiply 44.1kHz by a band from 20Hz to 20kHz, you get an upper sideband given 44.12kHz to 64.1kHz and a lower sideband from 44.08kHz down to 24.1kHz The highest modulating frequency for AM must be less than 1/2 the carrier frequency. Conversely, the lowest carrier frequency must be twice the highest modulating frequency. Period. I don't care what specific frequencies and/or energies and/or colors you propose. If you want to modulate at 20KHz, the carrier must be at least 40KHz. It is no coincidence that CD audio uses a 44.1KHz sample rate. It is essentially the same principle. If you exceed the Nyquist criterion, the sidebands overlap the baseband (i.e., aliasing occurs) and you cannot unambiguously decode the original modulation. Nyquist applies to sampling. So who is right and who is wrong? Look at the maths, it is never wrong. Modulating fc with fm gives a lowest frequency of fc-fm so as long as fc fm, you don't get aliasing. George So is it possible for me to receive a 10 KHz audio sine-wave tone on a 1 Hz AM radio receiver? If not, why? My guess is it violates Nyquist/ Shannon. Right? er i dont know any AM radio or any reciever that will recieve at 1Hz you surely mean 1 MHz which means that a 10 KHz tone would be easily modulated at that frequency |
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