Radium

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?


Thanks,

Radium

Sam Wormley

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?
>

Why would you expect a star to generate amplitude modulation?

Chris L Peterson

On Fri, 13 Jul 2007 20:04:13 GMT, Sam Wormley <swormley1@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

jimp@specsol.spam.sux.com

In rec.radio.amateur.space Radium <glucegen1@gmail.com> 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.

--
Jim Pennino

Remove .spam.sux to reply.

Radium

On Jul 13, 2:15 pm, j...@specsol.spam.sux.com wrote:
> In rec.radio.amateur.space Radium <gluceg...@gmail.com> 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?

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.

jimp@specsol.spam.sux.com

In rec.radio.amateur.space Radium <glucegen1@gmail.com> wrote:
> On Jul 13, 2:15 pm, j...@specsol.spam.sux.com wrote:
> > In rec.radio.amateur.space Radium <gluceg...@gmail.com> 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?

Generally, super cooled electronic components stop working.

Try again.

> 44.1 KHz is the carrier-frequency this hypothetical receiver receives.

A super stupid frequency to pick. Generally for listening for natural
phenomena, you want a wide as possible bandwidth given the noise
floor.

> 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.

Yeah, for digitized, audible music, you twit.

Are you expecting to hear alien rock and roll?

An AM receiver isn't digitizing anything, sample rates don't apply,
and aliasing doesn't apply.

Try again, idiot.

> 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.

Probably the only thing you got right.

--
Jim Pennino

Remove .spam.sux to reply.

Radium

On Jul 13, 4:55 pm, j...@specsol.spam.sux.com wrote:

> In rec.radio.amateur.space Radium <gluceg...@gmail.com> wrote:

> > 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?

> Generally, super cooled electronic components stop working.

Isn't a super cooled receiver less vulnerable to thermal noise than a
receiver of a higher temperature? This is why SETI super-cools their
radio receivers. So that the heat will not generate electric currents
that would drown-out the intended signals in hiss.

> > 44.1 KHz is the carrier-frequency this hypothetical receiver receives.

> A super stupid frequency to pick. Generally for listening for natural
> phenomena, you want a wide as possible bandwidth given the noise
> floor.

But humans only hear from 20 to 20,000 Hz. So why use a higher
frequency?

>From what you think, what is the best frequency for listening to
magnetars and other natural phenomena?

> > 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.

> An AM receiver isn't digitizing anything, sample rates don't apply,
> and aliasing doesn't apply.

Isn't it true that the carrier-frequency must be at least 2x the
highest intended frequency of the modulator signal?

I am not talking about sample rates. I am talking about carrier
frequency. From the answers to my previous questions regarding carrier
frequencies, I thought it was established that you mathematically
can't have a modulator frequency more than 0.5x the carrier-frequency.
What happened?

Since humans hear up to 20 KHz it is mathematically-required that the
carrier frequency be at least 40 KHz or 2 x 20 KHz. Due to physical
factors it would be most practical to use a carrier frequency slightly
higher than 2x the maximum intended modulator frequency -- hence 44.1
KHz.

jimp@specsol.spam.sux.com

In rec.radio.amateur.space Radium <glucegen1@gmail.com> wrote:
> On Jul 13, 4:55 pm, j...@specsol.spam.sux.com wrote:

> > In rec.radio.amateur.space Radium <gluceg...@gmail.com> wrote:

> > > 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?

> > Generally, super cooled electronic components stop working.

> Isn't a super cooled receiver less vulnerable to thermal noise than a
> receiver of a higher temperature? This is why SETI super-cools their
> radio receivers. So that the heat will not generate electric currents
> that would drown-out the intended signals in hiss.

> > > 44.1 KHz is the carrier-frequency this hypothetical receiver receives.

> > A super stupid frequency to pick. Generally for listening for natural
> > phenomena, you want a wide as possible bandwidth given the noise
> > floor.

> But humans only hear from 20 to 20,000 Hz. So why use a higher
> frequency?

> >From what you think, what is the best frequency for listening to
> magnetars and other natural phenomena?

> > > 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.

> > An AM receiver isn't digitizing anything, sample rates don't apply,
> > and aliasing doesn't apply.

> Isn't it true that the carrier-frequency must be at least 2x the
> highest intended frequency of the modulator signal?

> I am not talking about sample rates. I am talking about carrier
> frequency. From the answers to my previous questions regarding carrier
> frequencies, I thought it was established that you mathematically
> can't have a modulator frequency more than 0.5x the carrier-frequency.
> What happened?

> Since humans hear up to 20 KHz it is mathematically-required that the
> carrier frequency be at least 40 KHz or 2 x 20 KHz. Due to physical
> factors it would be most practical to use a carrier frequency slightly
> higher than 2x the maximum intended modulator frequency -- hence 44.1
> KHz.

If you had the slightest bit of education or common sense, you would
be asking a question that makes sense instead of going on forever
about the minutiae of what makes your questions idiotic.

Here's a question that makes sense:

Are there any sources of RF energy outside our solar system that
could possiblely be detected given an environment free of the
constraints of the ionsphere and man made noise?

If so, what frequecy or frequencies would they be seen at and what
would be the general characteristics of such a signal?

Also, the same question but operating from the Earth's surface.

And this is an astronomy/astro-physics question, not an electromagnetics
question.

Notice there is nothing in there about "supercooling", modulation
type, sampling rates, or any of the other nonsense in your question.

Babbling twit.


--
Jim Pennino

Remove .spam.sux to reply.

George Dishman

"Radium" <glucegen1@gmail.com> wrote in message
news:1184373407.506861.132200@m37g2000prh.googlegr oups.com...
...
> Isn't it true that the carrier-frequency must be at least 2x the
> highest intended frequency of the modulator signal?

No.

> I am not talking about sample rates. I am talking about carrier
> frequency. From the answers to my previous questions regarding carrier
> frequencies, I thought it was established that you mathematically
> can't have a modulator frequency more than 0.5x the carrier-frequency.

No. You can't have a sampling rate less than twice the highest
frequency in the source without aliasing, but that refers only
to sampling.

> What happened?

At a guess, you misunderstood the context of the answers to
your previous questions, or those who answered misunderstood
the context of your questions.

HTH
George

Andrew Smallshaw

On 2007-07-14, jimp@specsol.spam.sux.com wrote:
>
> If you had the slightest bit of education or common sense, you would
> be asking a question that makes sense instead of going on forever
> about the minutiae of what makes your questions idiotic.

This is Radium's usual posting style - to produce some random,
obvious ideas as if no one has ever considered them before, and
then to lightly dismiss any practical difficulties anyone points
out as trivial. After all, he's the genius, you're expected to
put in all the leg work to make a ridiculous idea actually work.

I've seen him all to many times before on the likes of
alt.comp.hardware.homebuilt. It's worth looking at the Goggle
archives to see just what nonsense he comes up with. My favourite
example is Radium's understanding of semiconductors:

> Why is silicon needed in the 1st place? For that matter, why any semi-
> conductor? Why not just use the copper electric circuits? Semi-
> conductors are half-way between conductor and insulator?

I think that that says it all.

--
Andrew Smallshaw
andrews@sdf.lonestar.org

Radium

On Jul 14, 1:17 am, "George Dishman" <geo...@briar.demon.co.uk> wrote:
> "Radium" <gluceg...@gmail.com> wrote in message
>
> news:1184373407.506861.132200@m37g2000prh.googlegr oups.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&
:

> 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.

So who is right and who is wrong? I am so interested yet so frustrated
over this!

I keep getting conflicting answers about this topic. Its driving me
crazy!!!!!!!!!!!!!!!!!

WTF is going on here??????????????????!!!!!!!!!!!!!!!!!!!!?!?!?!?! ?!

jimp@specsol.spam.sux.com

In rec.radio.amateur.space Radium <glucegen1@gmail.com> wrote:
> On Jul 14, 1:17 am, "George Dishman" <geo...@briar.demon.co.uk> wrote:
> > "Radium" <gluceg...@gmail.com> wrote in message
> >
> > news:1184373407.506861.132200@m37g2000prh.googlegr oups.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&
> :

> > 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.

> So who is right and who is wrong? I am so interested yet so frustrated
> over this!

> I keep getting conflicting answers about this topic. Its driving me
> crazy!!!!!!!!!!!!!!!!!

> WTF is going on here??????????????????!!!!!!!!!!!!!!!!!!!!?!?!?!?! ?!

WTF is going on is that you can't ask a meaningful question.

Here's some reality:

Q: Do extra terrestrial objects generate radio signals that can be heard
on Earth?

A. Yes, thousands and thousands of them. The field is called Radio
Astronomy. Google for more information.

Q: What frequency do they generate?

A: Basically, all of them. Most natural sources of RF are broad band
generators much like an electric arc.

Q: Where would one listen for signal?

A: Usually from around 1 GHz to hundreds of GHz. Some objects in the
solar system generate signals down into the tens of MHz but antenna
size and the ionosphere place a practical lower limit of around 100 MHz.

Q: Is the signal AM or FM or what?

A: None of the above. Modulation implies a carrier with information.
Natural objects generate broad band RF noise.

Q: Don't some of the sources vary in some way?

A: Some of them vary in magnitude over time, i.e. they get louder
and weaker periodically. Some sources are "bursty", i.e. most of
the time the are not there, then for some period of time they are.

Q: Do magnetars generate signals?

A: Some do, some don't seem to.

Q: Are these signals audible?

A: Depends on what you mean. If you hooked a speaker to a radio telescope,
you would hear white noise, i.e. a hissing sound much like what you
hear on an FM radio between stations.




--
Jim Pennino

Remove .spam.sux to reply.

George Dishman

"Radium" <glucegen1@gmail.com> wrote in message
news:1184446739.705444.308660@i38g2000prf.googlegr oups.com...
> On Jul 14, 1:17 am, "George Dishman" <geo...@briar.demon.co.uk> wrote:
>> "Radium" <gluceg...@gmail.com> wrote in message
>>
>> news:1184373407.506861.132200@m37g2000prh.googlegr oups.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

Sam Wormley

Chris L Peterson wrote:
> On Fri, 13 Jul 2007 20:04:13 GMT, Sam Wormley <swormley1@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


Amplitude modulation, in the communications world, has a definite
structure--I suspect that magnetar spectra don't exhibit amplitude
modulation characteristics.

However, I see, that amplitude modulation is appropriate in
astrophysics--for example...

Double Mode Cepheids with Amplitude Modulation
http://sait.oat.ts.astro.it/MSAIt770.....77..563M.pdf

Chris L Peterson

On Sat, 14 Jul 2007 23:36:08 GMT, Sam Wormley <swormley1@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

jimp@specsol.spam.sux.com

In rec.radio.amateur.space Sam Wormley <swormley1@mchsi.com> wrote:
> Chris L Peterson wrote:
> > On Fri, 13 Jul 2007 20:04:13 GMT, Sam Wormley <swormley1@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


> Amplitude modulation, in the communications world, has a definite
> structure--I suspect that magnetar spectra don't exhibit amplitude
> modulation characteristics.

> However, I see, that amplitude modulation is appropriate in
> astrophysics--for example...

> Double Mode Cepheids with Amplitude Modulation
> http://sait.oat.ts.astro.it/MSAIt770.....77..563M.pdf

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.

--
Jim Pennino

Remove .spam.sux to reply.

Chris L Peterson

On Sun, 15 Jul 2007 00:55:01 GMT, jimp@specsol.spam.sux.com 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.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Radium

On Jul 14, 4:11 pm, "George Dishman" <geo...@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?

jimp@specsol.spam.sux.com

In rec.radio.amateur.space Chris L Peterson <clp@alumni.caltech.edu> wrote:
> On Sun, 15 Jul 2007 00:55:01 GMT, jimp@specsol.spam.sux.com 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?

If the side lobes of a search radar are big enough, you can receive
them no matter where the radar points. The signal strength goes up
and down and goes up dramatically when you are swept by the main
lobe. Would you call that AM?

--
Jim Pennino

Remove .spam.sux to reply.

jimp@specsol.spam.sux.com

In rec.radio.amateur.space Radium <glucegen1@gmail.com> wrote:
> On Jul 14, 4:11 pm, "George Dishman" <geo...@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.

Radium

On Jul 14, 4:11 pm, "George Dishman" <geo...@briar.demon.co.uk> wrote:

> The relevant maths is:
>
> http://www.sosmath.com/trig/prodform/prodform.html
>

The above link says nothing about amplitude-modulation

KLM

Radium wrote:

> On Jul 13, 2:15 pm, j...@specsol.spam.sux.com wrote:
> > In rec.radio.amateur.space Radium <gluceg...@gmail.com> 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.

George Dishman

<jimp@specsol.spam.sux.com> wrote in message
news8mom4-on8.ln1@mail.specsol.com...
> In rec.radio.amateur.space Chris L Peterson <clp@alumni.caltech.edu>
> wrote:
>> On Sun, 15 Jul 2007 03:45:01 GMT, jimp@specsol.spam.sux.com 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

George Dishman

"Radium" <glucegen1@gmail.com> wrote in message
news:1184475933.510251.28100@j4g2000prf.googlegrou ps.com...
> On Jul 14, 4:11 pm, "George Dishman" <geo...@briar.demon.co.uk> 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

George Dishman

"Radium" <glucegen1@gmail.com> wrote in message
news:1184468634.242671.140830@i38g2000prf.googlegr oups.com...
> On Jul 14, 4:11 pm, "George Dishman" <geo...@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?

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

jimp@specsol.spam.sux.com

In rec.radio.amateur.space KLM <milk@mchsi.com> wrote:


> Radium wrote:

> > On Jul 13, 2:15 pm, j...@specsol.spam.sux.com wrote:
> > > In rec.radio.amateur.space Radium <gluceg...@gmail.com> 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.

Radium

On Jul 15, 3:35 am, "George Dishman" <geo...@briar.demon.co.uk> 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.

jimp@specsol.spam.sux.com

In rec.radio.amateur.space Radium <glucegen1@gmail.com> wrote:
> On Jul 15, 3:35 am, "George Dishman" <geo...@briar.demon.co.uk> 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?

Since all you are going to hear from astronomical sources is white
noise, it doesn't matter.

Aliasing is irrelevant.

The bigger issue with the frequency (other than plain stupidity) you
have choosen is that to be able to say you are hearing signals from
something specific in the sky as opposed to everything in the sky,
you need to have antenna directivity.

At a frequency of 44 KHz that means an antenna about 500 miles in
diameter and there isn't much that can be done to make it smaller.

--
Jim Pennino

Remove .spam.sux to reply.

Radium

On Jul 15, 10:05 am, j...@specsol.spam.sux.com wrote:

> The bigger issue with the frequency (other than plain stupidity) you
> have choosen is that to be able to say you are hearing signals from
> something specific in the sky as opposed to everything in the sky,
> you need to have antenna directivity.
>
> At a frequency of 44 KHz that means an antenna about 500 miles in
> diameter and there isn't much that can be done to make it smaller.

Why does it need to be around 500 miles? Atomic-clock wrist-watches
receive extremely long wavelengths and are able to do so with their
tiny sizes. Couldn't something similar be done for my 'application'?
If not, then why?