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Author: RadiumRadium Date: Jul 14, 2007 13:58
On Jul 14, 1:17 am, "George Dishman" briar.demon.co.uk> wrote:>> Isn't it true that the carrier-frequency must be at least 2x the
>> highest intended frequency of the modulator signal?
>
> No.
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Author: jimpjimp Date: Jul 14, 2007 15:15
In rec.radio.amateur.space Radium gmail.com> wrote:> On Jul 14, 1:17 am, "George Dishman" briar.demon.co.uk> wrote:>>> 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.
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Author: George DishmanGeorge Dishman Date: Jul 14, 2007 16:11
> On Jul 14, 1:17 am, "George Dishman" briar.demon.co.uk> wrote:>>> Isn't it true that the carrier-frequency must be at least 2x the
>>> highest intended frequency of the modulator signal?
>>
>> No.
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Author: Sam WormleySam Wormley Date: Jul 14, 2007 16:36
Chris L Peterson wrote:
> On Fri, 13 Jul 2007 20:04:13 GMT, Sam Wormley mchsi.com>
> wrote:
> >> Why would you expect a star to generate amplitude modulation?
>
> Why would you expect it to generate anything else? These sorts of
> objects are rotating at high speed, which modulates the amplitude we
> receive. While there are probably other types of modulation as well, the
> amplitude variation is the dominant effect. Of course, magnetars are
> emitting mainly hard x-rays. I don't know that there's enough long
> wavelength energy to detect on any kind of ordinary radio.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
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Author: Chris L PetersonChris L Peterson Date: Jul 14, 2007 17:44
On Sat, 14 Jul 2007 23:36:08 GMT, Sam Wormley mchsi.com>
wrote:
> Amplitude modulation, in the communications world, has a definite
> structure--I suspect that magnetar spectra don't exhibit amplitude
> modulation characteristics.
A magnetar is a type of pulsar. You have a signal at some frequency (or
range frequencies) that varies in amplitude with time (as the object
spins). That's the very definition of amplitude modulation. Nearly every
radio source around shows some degree of amplitude modulation as the
result of spin. This includes objects radiating well out of the radio
band, as well. Optical binaries exhibit AM. Starspots show up as AM.
Rotating asteroids are AM. Cepheids. Cataclysmic variables. Etc.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Author: jimpjimp Date: Jul 14, 2007 17:55
In rec.radio.amateur.space Sam Wormley mchsi.com> wrote:> Chris L Peterson wrote:
>> On Fri, 13 Jul 2007 20:04:13 GMT, Sam Wormley mchsi.com>
>> wrote:
>> >>> Why would you expect a star to generate amplitude modulation?
>>
>> Why would you expect it to generate anything else? These sorts of
>> objects are rotating at high speed, which modulates the amplitude we
>> receive. While there are probably other types of modulation as well, the
>> amplitude variation is the dominant effect. Of course, magnetars are
>> emitting mainly hard x-rays. I don't know that there's enough long
>> wavelength energy to detect on any kind of ordinary radio.
>>
>> _________________________________________________
>>
>> Chris L Peterson
>> Cloudbait Observatory
>> http...
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Author: Chris L PetersonChris L Peterson Date: Jul 14, 2007 18:46
>The definitions for all types of modulation involve a carrier frequency.
>
>Since natural phenomena generate broad band noise, it is arm waving
>at best to call the variations in amplitude "amplitude modulation".
>
>What it is is a broad band source that periodically varies in signal
>strength.
There's nothing that defines how narrow a band need be to qualify as a
"carrier". Many modern communication systems are spread spectrum, which
means the carrier may be very broad. Such systems are certainly
modulated. Also, many astronomical sources are not broadband at all, but
radiate across a narrow spectrum.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Author: RadiumRadium Date: Jul 14, 2007 20:03
On Jul 14, 4:11 pm, "George Dishman" briar.demon.co.uk> 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?
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Author: jimpjimp Date: Jul 14, 2007 20:45
In rec.radio.amateur.space Chris L Peterson alumni.caltech.edu> wrote:>>The definitions for all types of modulation involve a carrier frequency.
>>
>>Since natural phenomena generate broad band noise, it is arm waving
>>at best to call the variations in amplitude "amplitude modulation".
>>
>>What it is is a broad band source that periodically varies in signal
>>strength.
> There's nothing that defines how narrow a band need be to qualify as a
> "carrier". Many modern communication systems are spread spectrum, which
> means the carrier may be very broad. Such systems are certainly
> modulated. Also, many astronomical sources are not broadband at all, but
> radiate across a narrow spectrum.
Spread spectrum technology uses discrete frequency hopping, not a
broad band signal as a carrier.
If I have a transmitter hooked to an antenna swaying in the breeze
such that the received signal strength is varying, would you call
that AM?
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Author: jimpjimp Date: Jul 14, 2007 20:45
In rec.radio.amateur.space Radium gmail.com> wrote:> On Jul 14, 4:11 pm, "George Dishman" briar.demon.co.uk> 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?
What part of "as long as fc is greater that fm" are you too blazingly
stupid to understand?
Is 10 KHz bigger than 10 KHz?
Idiot.
--
Jim Pennino
Remove .spam.sux to reply.
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