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Do magnetars emit audible LW AM radio waves that can be heard on receivers?
On Jul 14, 4:11 pm, "George Dishman" wrote:
The relevant maths is: http://www.sosmath.com/trig/prodform/prodform.html The above link says nothing about amplitude-modulation |
#22
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Do magnetars emit audible LW AM radio waves that can be heard onreceivers?
Radium wrote: On Jul 13, 2:15 pm, wrote: In rec.radio.amateur.space Radium wrote: Hi: Do magnetars emit AM radio waves below the medium-wave range? If so, how do we detect these waves? Can these waves be heard on the AM radio? If so, what do they sound like? Frequencies above approximately 100 MHz almost always get through the ionization layers. Frequencies in the approximate range of 10 MHz to 100 MHz sometimes get through Frequencies below approximately 10 MHz almost never get through. So, if by "the AM radio" you mean a Broadcast Band radio which runs from about .5 MHz to 1.2 MHz, not a chance in hell of ever hearing anything from off the planet. Try again. Okay. But what if this is a supercooled AM radio receiver on a spaceship orbiting Earth? If I am on a space station like MIR and this station has a supercooled AM radio 44.1 KHz frequency receiver, will I hear anything specific of magnetars? Nothing "specific". Thats the whole point. What exactly did you hope to hear that you think is significant? Obviously you have something in mind. KLM 44.1 KHz is the carrier-frequency this hypothetical receiver receives. I place the frequency of this hypothetical AM radio carrier wave at 44.1 KHz for the same reason CDs use a sample rate of 44.1 KHz -- it is the minimum required to prevent aliasing. AFAIK, space station orbit earth above the ionosphere so the limitations [preventing long-waves from outer space from reaching the Earth's surface] do not apply. |
#23
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Do magnetars emit audible LW AM radio waves that can be heard on receivers?
wrote in message news In rec.radio.amateur.space Chris L Peterson wrote: On Sun, 15 Jul 2007 03:45:01 GMT, wrote: Spread spectrum technology uses discrete frequency hopping, not a broad band signal as a carrier. That is correct, it is a narrow band carrier which moves. That's one spread spectrum method. Not the only one. But regardless, it still presents as a broad band carrier. Nope, all spread spectrum is based on discrete frequencies with frequency hopping of some sort. Not always, consider the use of a frequency-shifted fast PRBS as the carrier. Of course it is more usual to use the PRBS to define the hop sequence in the style you describe above but as you say your background is communications, I'm sure you are aware of the relationships between hop rate and carrier spacing which lead to a band-limited white spectrum. AM is a variation in amplitude of some signal- any signal- with time. Nope, mathematically AM is defined as a single carrier frequency multipled by the modulation frequency. That you get a variation in amplitude is an effect, not a definition. It is a bit of a stretch to call a signal comprised of every frequency over a 100 GHz span AM. Consider applying audio (with a DC bias) to a light bulb and receiving it with a photocell. The carrier is much more than 100 GHz wide, but I would still call that AM, YMMV. I'm afraid my background IS communications ... Mine too ;-) George |
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Do magnetars emit audible LW AM radio waves that can be heard on receivers?
"Radium" wrote in message ps.com... On Jul 14, 4:11 pm, "George Dishman" wrote: The relevant maths is: http://www.sosmath.com/trig/prodform/prodform.html The above link says nothing about amplitude-modulation It says: sin(a)sin(b) = 1/2 * [ cos(a-b) - cos(a+b) ] Take a carrier at frequency fc: Vc = sin(2*pi*fc*t) and a typical modulating signal at fm: Vm = sin(2*pi*fm*t) Amplitude modulation involves multiplying those together with an offset so that there is always some level of carrier so the transmitted signal is: Vt = Vc * (1 + M * Vm) where 0 M 1 You get components at cos(2*pi*(fc-fm)*t) and cos(2*pi*(fc+fm)*t) as well as the carrier at fc. George |
#25
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Do magnetars emit audible LW AM radio waves that can be heard on receivers?
"Radium" wrote in message oups.com... On Jul 14, 4:11 pm, "George Dishman" wrote: 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. So an fm of 10 KHz would work on an fc of 10 KHz? fc fm means fc should be greater than fm, not the same. For fm = 10,000Hz and fc = 10,001Hz you get a lower sideband at 1Hz and an upper sideband at 20,001Hz. If you modulate 10kHz with 10Khz, the lower sideband becomes 0Hz or DC. The value of that depends on the phase of the modulating signal relative to the carrier (which is now constant since they are at the same frequency). Of course sending DC to an antenna won't give you a transmitted signal but it doesn't produce an alias either. If you modulate 10,000Hz with 10,001Hz then your lower sideband becomes -1Hz, and of course sin(-x) = sin(x) so that is identical to a frequency of 1Hz which you would get if you modulated with 9,999Hz. That ambiguity is why we call such a signal an "alias", the 10,001Hz signal appears after modulation then demodulation masquerading as a signal of 9,999Hz. George |
#27
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Do magnetars emit audible LW AM radio waves that can be heard on receivers?
In rec.radio.amateur.space George Dishman wrote:
wrote in message news In rec.radio.amateur.space Chris L Peterson wrote: On Sun, 15 Jul 2007 03:45:01 GMT, wrote: Spread spectrum technology uses discrete frequency hopping, not a broad band signal as a carrier. That is correct, it is a narrow band carrier which moves. That's one spread spectrum method. Not the only one. But regardless, it still presents as a broad band carrier. Nope, all spread spectrum is based on discrete frequencies with frequency hopping of some sort. Not always, consider the use of a frequency-shifted fast PRBS as the carrier. Of course it is more usual to use the PRBS to define the hop sequence in the style you describe above but as you say your background is communications, I'm sure you are aware of the relationships between hop rate and carrier spacing which lead to a band-limited white spectrum. If you frequency or phase modulate, the resultant spectrum may be quite broad, but the carrier frequency is still discreate no matter what you modulate with. It may look like band limited white noise on a spectrum analyser, but if you decompose in the time domain, it isn't. AM is a variation in amplitude of some signal- any signal- with time. Nope, mathematically AM is defined as a single carrier frequency multipled by the modulation frequency. That you get a variation in amplitude is an effect, not a definition. It is a bit of a stretch to call a signal comprised of every frequency over a 100 GHz span AM. Consider applying audio (with a DC bias) to a light bulb and receiving it with a photocell. The carrier is much more than 100 GHz wide, but I would still call that AM, YMMV. Got me there. I'm afraid my background IS communications ... Mine too ;-) George -- Jim Pennino Remove .spam.sux to reply. |
#28
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Do magnetars emit audible LW AM radio waves that can be heard on receivers?
In rec.radio.amateur.space Chris L Peterson wrote:
On Sun, 15 Jul 2007 05:05:01 GMT, wrote: Nope, all spread spectrum is based on discrete frequencies with frequency hopping of some sort. I would not consider that to be an accurate description for a variety of direct sequence techniques, where the carrier itself is phase or frequency modulated by a pseudorandom sequence. Such a signal, viewed on a spectrum analyzer, looks no different than many natural, moderately narrowband sources. And there would be nothing stopping somebody from amplitude modulating such a signal. If you frequency or phase modulate, the spectrum does get broad, but there is still a discreat carrier frequency. While it may look like band limited white noise on a vanilla spectrum analyzer, it isn't. Nope, mathematically AM is defined as a single carrier frequency multipled by the modulation frequency. That you get a variation in amplitude is an effect, not a definition. Reference? I think you are confusing a single definition of AM with all other definitions of the term. How about this one: http://www.rfcafe.com/references/ele...modulation.htm I'm afraid my background IS communications so I have to say astronomers are arm waving when they call astronomical signals AM unless ET is phoning home. As an astronomer, I could as easily say you are arm waving by trying to restrict the meaning of AM to a narrow definition used within your field. The simple fact is that astronomers _do_ refer to signals that vary in amplitude as a function of time as "amplitude modulated". Some of those signals are broadband, and others are not (there are, for example, amplitude modulated natural masers). This is normal usage within the astronomical community, and it causes no confusion at all. So, is the square root of -1 j or i? -- Jim Pennino Remove .spam.sux to reply. |
#29
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Do magnetars emit audible LW AM radio waves that can be heard on receivers?
In rec.radio.amateur.space KLM wrote:
Radium wrote: On Jul 13, 2:15 pm, wrote: In rec.radio.amateur.space Radium wrote: Hi: Do magnetars emit AM radio waves below the medium-wave range? If so, how do we detect these waves? Can these waves be heard on the AM radio? If so, what do they sound like? Frequencies above approximately 100 MHz almost always get through the ionization layers. Frequencies in the approximate range of 10 MHz to 100 MHz sometimes get through Frequencies below approximately 10 MHz almost never get through. So, if by "the AM radio" you mean a Broadcast Band radio which runs from about .5 MHz to 1.2 MHz, not a chance in hell of ever hearing anything from off the planet. Try again. Okay. But what if this is a supercooled AM radio receiver on a spaceship orbiting Earth? If I am on a space station like MIR and this station has a supercooled AM radio 44.1 KHz frequency receiver, will I hear anything specific of magnetars? Nothing "specific". Thats the whole point. What exactly did you hope to hear that you think is significant? Obviously you have something in mind. KLM What makes you think there is anything in that mind other than a bunch of technical words and terms strung together in a random manner? -- Jim Pennino Remove .spam.sux to reply. |
#30
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Do magnetars emit audible LW AM radio waves that can be heard on receivers?
On Jul 15, 3:35 am, "George Dishman" wrote:
fc fm means fc should be greater than fm, not the same. For fm = 10,000Hz and fc = 10,001Hz you get a lower sideband at 1Hz and an upper sideband at 20,001Hz. Sorry. I didn't read it correctly. If you modulate 10kHz with 10Khz, the lower sideband becomes 0Hz or DC. The value of that depends on the phase of the modulating signal relative to the carrier (which is now constant since they are at the same frequency). Of course sending DC to an antenna won't give you a transmitted signal but it doesn't produce an alias either. If you modulate 10,000Hz with 10,001Hz then your lower sideband becomes -1Hz, and of course sin(-x) = sin(x) so that is identical to a frequency of 1Hz which you would get if you modulated with 9,999Hz. That ambiguity is why we call such a signal an "alias", the 10,001Hz signal appears after modulation then demodulation masquerading as a signal of 9,999Hz. Does this mean an fm of 10 KHz would work on an fc of 10.0000000000000000000001 KHz? If so, then the minimum frequency required for my "project" would be only 20.0000000000000000001 KHz. Or just anything above 20 KHz, even if it's just an extremely extremely small number above 20,000. Right? I apologize if readers find my question annoying. To all: I have a neurological disability called Asperger's Syndrome. I would like to give you some information about my disability. The reason I am posting this message about Asperger's is to help avoid any potential misunderstandings [though it's probably too late]. I have been diagnosed with Asperger's Syndrome (AS). AS is a neurological condition that causes significant impairment in social interactions. People with AS see the world differently and this can often bring them in conflict with conventional ways of thinking. They have difficulty in reading body language, and interpreting subtle cues. In my situation, I have significant difficulty with natural conversation, reading social cues, and maintaining eye contact. This can lead to a great deal of misunderstanding about my intent or my behavior. For example, I may not always know what to say in social situations, so I may look away or may not say anything. I also may not always respond quickly when asked direct questions, but if given time I am able express my ideas. On Usenet, the text-equivalent of my disability is probably noticed. I do apologize profusely, for any inconvenience it causes. Thank you very much in advance for your understanding, cooperation, and assistance. |
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