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AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency

R

RHF

Jan 1, 1970
0
Radium:

Use simple logic, you can modulate a dc (0 Hz) with higher freq (voice),
(hint, your telephone line is an example) right?

However, when you get into RF--possible, usable, desirable are seperate
and distinct things.

Again, with simple logic, modulating a 30 CPS signal with limited voice
freq (say 5K wide) is going to create a LOT of harmonics and mixed
signals, ain't it? Suggesting a very wide band receiver would be needed
to begin with ... in my humble opinion, and for various reasons, NO, it
is NOT possible ...

Regards,
JS
 
R

RHF

Jan 1, 1970
0
["Followup-To:" header set to sci.electronics.basics.]
Radium wrote:
WTF are you thinking when you describe the 20 Khz signal as, "a
pure-sine-wave-tone] with a frequency of 20 KHz and an
amplitude of 1-watt-per-meter-squared"

Candela

Admittedly an odd unit to use for radiation at that frequency.

Bye.
Jasen
 
R

RHF

Jan 1, 1970
0
- "Radium" is a well known "Troll".
- When he runs low/out of meds and tin foil he will
- post this techo-babble crap all over usenet.
- Just add him to your killfile list.
- "Radium" is a "Throw-away"....a complete waste of time......

PT - Then why waste your time replying to his posts ?

IMHO - In another life "Radium" would have made
a great High School Science Teacher :
Who's Students when on to do great things with
their lives :
Because "Radium" Touched Them With A Thirst
For Knowledge And A Quest For Answers.

-but- These NewsGroups are NOT a High School
Science Class -and- "Radium" is just being 'radium'.
http://en.wikipedia.org/wiki/Radium

-alas- Our "Radium's" Half-Life of Readable Interest
http://en.wikipedia.org/wiki/Half-life
is at best about 16.04 Seconds ~ RHF
 
R

RHF

Jan 1, 1970
0
RADIUM,

IMHO - In another life "Radium" you would have
made a great High School Science Teacher :
Who's Students when on to do great things with
their lives :
Because You "Radium" Touched Them With A
Thirst For Knowledge And A Quest For Answers.

-but- These NewsGroups are NOT a High School
Science Class -and- "Radium" you are just being
'radium'. => http://en.wikipedia.org/wiki/Radium
decaying into a gas and dispersing into nothingness.
http://en.wikipedia.org/wiki/Radon

-alas- "Radium" Your Half-Life of Readable Interest
http://en.wikipedia.org/wiki/Half-life
is at best about 16.04 Seconds ~ RHF
 
J

John Smith I

Jan 1, 1970
0
RHF said:
...
Because "Radium" Touched Them With A Thirst
For Knowledge And A Quest For Answers.
...

I don't know, according to any instructor I have ever had respect for:
"There are NO stupid questions, only stupid people who are afraid to ask
questions."

Depends ... I guess.

JS
 
D

Don Bowey

Jan 1, 1970
0
Why not?

I am getting conflicting answers. Some say it's possible to modulate a
carrier frequency at a frequency higher than the carrier frequency,
others say it isn't.

Partly it's because you formulate piss poor questions.
Who is right?

Neither if stated as an "absolute rule," a.k.a. a Universal Generalization.
It depends on what you want as a result. However, IMHO opinion, I believe
it is best to have the Carrier at a higher frequency than the modulating
frequency.

If you are amplitude modulating a Carrier with a voice band signal, then it
is mandatory, for a reasonable result, that the Carrier have a much higher
frequency than the modulating frequency.

If you are AM modulating (a.k.a. RF mixing or converting) two signals for
the purpose of creating sum and difference "Carriers" in, for example, a
synthesizer, you could use the low frequency to "modulate" the high
frequency frequency, but I don¹t recommend it unless some special effect is
desired.


Start with the question of what is it you wish to accomplish then ask real
questions, not some far-out hypothetical drivel.
 
R

RHF

Jan 1, 1970
0
Partly it's because you formulate piss poor questions.




Neither if stated as an "absolute rule," a.k.a. a Universal Generalization.
It depends on what you want as a result. However, IMHO opinion, I believe
it is best to have the Carrier at a higher frequency than the modulating
frequency.

If you are amplitude modulating a Carrier with a voice band signal, then it
is mandatory, for a reasonable result, that the Carrier have a much higher
frequency than the modulating frequency.

If you are AM modulating (a.k.a. RF mixing or converting) two signals for
the purpose of creating sum and difference "Carriers" in, for example, a
synthesizer, you could use the low frequency to "modulate" the high
frequency frequency, but I don¹t recommend it unless some special effect is
desired.

Start with the question of what is it you wish to accomplish then ask real
questions, not some far-out hypothetical drivel.

.
 
M

Mike Kaliski

Jan 1, 1970
0
Radium said:
Why not?

I am getting conflicting answers. Some say it's possible to modulate a
carrier frequency at a frequency higher than the carrier frequency,
others say it isn't.

Who is right?
Radium

Me

Read my entire earlier reply. Then go to the library and spend several years
reading through the electronics section with particular emphasis on the
origins of electrical technology and early wireless. Then take a technical
biased university course incorporating logic and critical analysis and all
will become clear.

Without a basic knowledge of the subject, you are unable to make any form of
critical judgement as to the accuracy or correctness of what people are
telling you and all your questions become valueless because you do not have
the nous to evaluate the answers you receive.

Start with the basics and then try working up from there. Many inadvisable
things are technically possible, putting a dead short across the mains will
generate a pretty good example of electromagnetic pulse, but it is far
better to use a capacitive discharge circuit to do the same job. You could
try modulating carriers at all different sorts of frequencies to generate
harmonics, far better to use a square wave generator. You get the idea.

Regards

Mike G0ULI
 
J

Jeff Liebermann

Jan 1, 1970
0
Radium said:

Unfortunately, this is a good question and literally the first and
probably only good question you've asked so far. Yes, it's possible,
but you won't get the results you're expecting. See below.
I am getting conflicting answers. Some say it's possible to modulate a
carrier frequency at a frequency higher than the carrier frequency,
others say it isn't.

Who is right?

What does my politics have to do with anything? For what it's worth,
I'm politically somewhat left of center on most of my views.

An AM modulator is just a simple multiplier (mixer). The modulator
takes two signals, multiplies (or mixes) them together, and produces
an amplitude modulated output. For one of about 10 assorted JAVA
applets Google found that illustrate the waveforms see:
<http://cnyack.homestead.com/files/modulation/modam.htm>
Lots more at:
<http://www.educypedia.be/electronics/javamodulation.htm>

Note that a simple multiplier (mixer) doesn't care which frequency is
the carrier and which is the modulation. The two input ports are
essentially identical. The carrier is always higher in fequency than
the modulation input. If your derranged experiment somehow causes the
modulation input frequency to exceed the carrier frequency, the
multiplier produces exactly the same output as if the frequencies were
reversed. The modulation frequency becomes the carrier, and the
carrier frequency becomes the modulation input. In other words, with
AM it doesn't matter which input is the higher frequency, the output
is exactly the same.

If you happen to own some audio test equipment, you can easily
demonstrate this with two audio oscillators, a mixer of some sorts,
and an oscilloscope. Setup the equipment with two different input
frequencies and look at the output waveform. Now, swap inputs and
look again. It's the same. There's no question of which input is
modulating which other input. With AM, it's ALWAYS the high frequency
that acts as the carrier and the lower that acts as the modulation.

Now, please go back to your cave and read something on the basics of
modulation. If words confuse you, see the above JAVA applets which
will do it with pictures.
 
C

cledus

Jan 1, 1970
0
Radium said:
Hi:

Please don't be annoyed/offended by my question as I decreased the
modulation frequency to where it would actually be realistic.

I have a very weird question about electromagnetic radiation,
carriers, and modulators.

Is it mathematically-possible to carry a modulator signal [in this
case, a pure-sine-wave-tone] with a frequency of 20 KHz and an
amplitude of 1-watt-per-meter-squared on a AM carrier signal whose
frequency is 10^-(1,000,000,000-to-the-power-10^1,000,000,000)
nanocycle* every 10^1,000,000,000-to-the-power-10^1,000,000,000 giga-
eons and whose amplitude is a minimum of 10^1,000,000,000-to-the-
power-10^1,000,000,000 gigaphotons per 10^-(1,000,000,000-to-the-
power-10^1,000,000,000) nanosecond?

If it is not mathematically-possible, then please explain why.

10^-(1,000,000,000-to-the-power-10^1,000,000,000) second is an
extremely short amount of time. 10^-(1,000,000,000-to-the-
power-10^1,000,000,000) nanosecond is even shorter because a
nanosecond is shorter than a second.

Giga-eon = a billion eons

Eon = a billion years

*nanocycle = billionth of a cycle

Gigaphoton = a billion photons

10^1,000,000,000-to-the-power-10^1,000,000,000 -- now that is one
large large number.

10^1,000,000,000 = 10-to-the-power-1,000,000,000

So you get:

(10-to-the-power-1,000,000,000) to the power (10-to-the-
power-1,000,000,000)

10^-(1,000,000,000-to-the-power-10^1,000,000,000) = 10^-(10-to-the-
power-1,000,000,000)-to-the-power-(10-to-the-power-1,000,000,000)

10^-(10-to-the-power-1,000,000,000) to the power (10-to-the-
power-1,000,000,000) is an extremely small number at it equals 10-to-
the-power-NEGATIVE-[(10-to-the-power-1,000,000,000) to the power (10-
to-the-power-1,000,000,000)]

No offense but please respond with reasonable answers & keep out the
jokes, off-topic nonsense, taunts, insults, and trivializations. I am
really interested in this.


Thanks,

Radium


The fundamental answer is no, it is not possible to generate AM where
the baseband signal is a pure 20 kHz sinewave and Fc<20kHz. The reason
is that the modulated waveform consists of the sum of a sinewave at Fc,
a sinewave at Fc+20kHz, and a sinewave at Fc-20kHz. If Fc<20kHz then
one of the components becomes a "negative" frequency. So the carrier
must be greater than the baseband signal to prevent this.

It is conceivable that you could make Fc a miniscule number higher than
20kHz. However, if you want to radiate the signal efficiently, you will
need an antenna that is miles long. That is why most radios operate
with carrier frequencies much higher than the audio range. Antennas
become much more practical at frequencies in the MHz range.

You might enjoy a good book that provides fundamentals of electronics
and radio. Pick up a copy of the ARRL Handbook (www.arrl.org), for
example. That should help you pick up some of these concepts.
 
R

Radium

Jan 1, 1970
0
With AM, it's ALWAYS the high frequency
that acts as the carrier
and the lower that acts as the modulation.

In AM, isn't the carrier the signal which always maintains a constant
frequency and only varies by amplitude?

If a carrier signal varies by anything other than just amplitude, then
it isn't AM. Right?
 
J

John Smith I

Jan 1, 1970
0
Radium said:
...
If a carrier signal varies by anything other than just amplitude, then
it isn't AM. Right?

Let logic be your guide, again. As was pointed out earlier, the voice
freqs which modulate the carrier will cause a variance in freq (a small
fm component.)

In fm, it is not unusual for a small "amplitude modulation" to be
generated, as the varying/spanning of freq(s) is caused by the
modulation, some changes in fm carrier can be generated.

In an imperfect world, nothing is "perfect."

Regards,
JS
 
J

Jeff Liebermann

Jan 1, 1970
0
In AM, isn't the carrier the signal which always maintains a constant
frequency and only varies by amplitude?

You really are clueless. The carrier does NOT vary in amplitude. If
it did, that would be modulating the carrier, which is the job of the
modulator, not whatever is producing the carrier. You could have two
modulators in series, that would make the circuit overly complicated.
Please re-read my highly simplified previous explanation about the
symmetry of the AM multiplier (mixer) input ports until it's absorbed
and understood by your porous brain.

Incidentally, the reason I keep using the term "multiplier (mixer)" is
to avoid confusion with a harmonic multiplier. An AM modulator is a
mixer, not a harmonic multiplier.

Also, the carrier might remain constant frequency, for a given FCC
channel assignment, but the modulation is all over the place. For
example, your voice goes from 300 to 3000Hz, all of which is fed to
the modulator for digestion.

Conventional TV is VSB (visidual side band) which is a form of AM with
one of the two side bands partially removed, usually by filtering.
There's a carrier 1.25MHz offset for the video, another carrier 4.5Mhz
offset for the audio, and whatever else they can throw in for low
speed data. Two more more carriers are required for TV+audio.

If you want to get really high-techy, the new digital modes (DRM,
iBiquity, HD Radio, etc) all have multiple carriers, each of which is
modulated individually. Same with various OFDM modes, which have
multiple carriers, individually modulated and positioned orthogonally
from each other to prevent mutual interference from adjacent modulated
carriers.
If a carrier signal varies by anything other than just amplitude, then
it isn't AM. Right?

Wrong. The carrier can also vary, such as in a sweep generator or
jammer. It's not commonly done but it's possible. Want to obliterate
the entire AM broadcast band? No problem. Just sweep the carrier
from 530KHz to 1650KHz, while modulating the 300 to 3000Hz audio with
a rendition of your incoherent ranting.

By the way, you're welcome.
 
M

Mike Kaliski

Jan 1, 1970
0
Radium said:
In AM, isn't the carrier the signal which always maintains a constant
frequency and only varies by amplitude?

If a carrier signal varies by anything other than just amplitude, then
it isn't AM. Right?

Essentially correct. The sidebands either side of the central carrier wave
contain the modulation information.

If the carrier wave were to shift in frequency then that would be frequency
modulation.

Before you ask, yes it is possible to have an AM signal modulating an FM one
and several other wonderful combinations involving phase transformations,
variable pulse widths and sideband(s) only. It is all detailed in the ARRL
Handbook, RSGB Handbook and many other prestigious publications.

Mike G0ULI
 
R

Radium

Jan 1, 1970
0
The carrier does NOT vary in amplitude. If
it did, that would be modulating the carrier, which is the job of the
modulator, not whatever is producing the carrier.

Exactly. The modulator signal modulates the carrier wave. If there is
no modulator signal, then the carrier does not vary by amplitude or by
anything.

One poster stated that the signal with the higher-frequency is
automatically the carrier wave while the signal with the lower-
frequency is automatically the modulator wave. This is not true. What
I was trying to say is that an AM radio carrier wave cannot vary
significantly by anything other than its amplitude [though, as one
poster pointed out, the AM carrier can experience extremely-negligible
variations in frequency]. If an AM radio signal has that restriction,
it is the carrier wave. If an AM radio signal does not have that
restriction, then it is the modulator wave. This is true, even if the
AM carrier wave is of a lower-frequency than the modulator wave.
That's what I was trying to say.

In AM radio, determining which is the carrier wave and which is the
modulator wave is not by which has the higher frequency but rather by
which has the restriction that I stated.

If there is no modulator signal, then no carrier signal of any type
[AM, FM, etc.] will vary by any quality [frequency, amplitude, phase,
etc.]
 
D

Don Bowey

Jan 1, 1970
0
In AM, isn't the carrier the signal which always maintains a constant
frequency and only varies by amplitude?

No! The Carrier amplitude is constant. Sidebands are generated in the
modulation process. At 100% modulation, each sideband has 25% as much power
as the Carrier. The sideband signals vary in amplitude, following the
modulation signal.

If a carrier signal varies by anything other than just amplitude, then
it isn't AM. Right?

You repeat yourself, and the answer is still no.
 
D

Don Bowey

Jan 1, 1970
0
Let logic be your guide, again. As was pointed out earlier, the voice
freqs which modulate the carrier will cause a variance in freq (a small
fm component.)

This will not happen in a properly designed transmitter. It is not a
characteristic of AM.
 
D

Don Bowey

Jan 1, 1970
0
You really are clueless. The carrier does NOT vary in amplitude. If
it did, that would be modulating the carrier, which is the job of the
modulator, not whatever is producing the carrier. You could have two
modulators in series, that would make the circuit overly complicated.
Please re-read my highly simplified previous explanation about the
symmetry of the AM multiplier (mixer) input ports until it's absorbed
and understood by your porous brain.

Incidentally, the reason I keep using the term "multiplier (mixer)" is
to avoid confusion with a harmonic multiplier. An AM modulator is a
mixer, not a harmonic multiplier.

Also, the carrier might remain constant frequency, for a given FCC
channel assignment, but the modulation is all over the place. For
example, your voice goes from 300 to 3000Hz, all of which is fed to
the modulator for digestion.

Conventional TV is VSB (visidual side band) which is a form of AM with
one of the two side bands partially removed, usually by filtering.
There's a carrier 1.25MHz offset for the video, another carrier 4.5Mhz
offset for the audio, and whatever else they can throw in for low
speed data. Two more more carriers are required for TV+audio.

If you want to get really high-techy, the new digital modes (DRM,
iBiquity, HD Radio, etc) all have multiple carriers, each of which is
modulated individually. Same with various OFDM modes, which have
multiple carriers, individually modulated and positioned orthogonally
from each other to prevent mutual interference from adjacent modulated
carriers.


Wrong. The carrier can also vary, such as in a sweep generator or
jammer. It's not commonly done but it's possible. Want to obliterate
the entire AM broadcast band? No problem. Just sweep the carrier
from 530KHz to 1650KHz, while modulating the 300 to 3000Hz audio with
a rendition of your incoherent ranting.

By the way, you're welcome.


You are getting far afield of classical AM, which is the subject of Radium's
post. He is confused and you aren't helping.
 
D

Don Bowey

Jan 1, 1970
0
The carrier does NOT vary in amplitude. If
it did, that would be modulating the carrier, which is the job of the
modulator, not whatever is producing the carrier.

Exactly. The modulator signal modulates the carrier wave. If there is
no modulator signal, then the carrier does not vary by amplitude or by
anything.

One poster stated that the signal with the higher-frequency is
automatically the carrier wave while the signal with the lower-
frequency is automatically the modulator wave. This is not true. What
I was trying to say is that an AM radio carrier wave cannot vary
significantly by anything other than its amplitude [though, as one
poster pointed out, the AM carrier can experience extremely-negligible
variations in frequency]. If an AM radio signal has that restriction,
it is the carrier wave. If an AM radio signal does not have that
restriction, then it is the modulator wave. This is true, even if the
AM carrier wave is of a lower-frequency than the modulator wave.
That's what I was trying to say.

In AM radio, determining which is the carrier wave and which is the
modulator wave is not by which has the higher frequency but rather by
which has the restriction that I stated.

If there is no modulator signal, then no carrier signal of any type
[AM, FM, etc.] will vary by any quality [frequency, amplitude, phase,
etc.]

You should just recall that post.
 
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