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

"Radium" wrote in message
ups.com...
On Jun 30, 3:46 pm, Jeff Liebermann wrote:

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?


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

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

On Jun 30, 7:43 pm, Jeff Liebermann wrote:

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.]

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

On 6/30/07 7:01 PM, in article
, "Radium"
wrote:

On Jun 30, 3:46 pm, Jeff Liebermann wrote:

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?

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.

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

On 6/30/07 7:31 PM, in article , "John Smith I"
wrote:

Radium wrote:

...
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.)

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

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

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

On 6/30/07 7:43 PM, in article ,
"Jeff Liebermann" wrote:

Radium hath wroth:

On Jun 30, 3:46 pm, Jeff Liebermann wrote:

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?

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.



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

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

On 6/30/07 8:01 PM, in article
, "Radium"
wrote:

On Jun 30, 7:43 pm, Jeff Liebermann wrote:

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.

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

Don Bowey wrote:

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


Listen to a "strong--pure am signal" on an fm receiver, turn up the
volume on the fm receiver, something is responsible for that ... repeat
experiment with the reverse ... "imperfect world theory" proof!

In new equip (I started out decades ago, remember) voltage regulation,
filters, suppressors have much improved ... digital processing is king
and allows what analog never could achieve ...

Regards,
JS

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

On 6/30/07 8:29 PM, in article , "John Smith I"
wrote:

Don Bowey wrote:

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


Listen to a "strong--pure am signal" on an fm receiver, turn up the
volume on the fm receiver, something is responsible for that ... repeat
experiment with the reverse ... "imperfect world theory" proof!

You are hearing the effects of the sidebands, not the Carrier.


In new equip (I started out decades ago, remember) voltage regulation,
filters, suppressors have much improved ... digital processing is king
and allows what analog never could achieve ...

Regards,
JS

In a properly designed transmitter the Carrier amplitude does not change
with modulation. I have better tools than FM receivers to prove that fact
and theory agree for AM.

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

Radium hath wroth:

On Jun 30, 7:43 pm, Jeff Liebermann wrote:

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.

Brilliant. Yes, if there is no signal input, there's no change in
output.

Incidentally, in an AM system, the carrier does NOT change. You can
see that on a spectrum analyzer. Modulate all you want and the
carrier stays put at 50% of the total power output. The rest of the
power is split between the upper and lower side bands. If there is no
modulation input, then the side bands disappear, but the carrier just
stays there.

As someone mentioned, there is usually some residual FM on the carrier
usually caused by sloppy power supply regulation. Also, some
synthesizer noise. A well designed AM broadcast transmitter doesn't
have much of this junk present. The problem is that the FM that
appears on the carrier also appears on all the side bands. It doesn't
hurt if the carrier has a little residual FM, but any such junk on the
sidebands will result in a substantial increase in audible noise by
mixing with the audio.

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.

That was me.

This is not true.

Prove it. I explained how it works and why quite adequately. I
didn't even need to resort to formulas and calculations. The
multiplier (mixer) modulator inputs are symmetrical and identical.
Therefore the inputs are also symmetrical and indistinguishable. I
also provided a simple audio test you can do in your spare time to
demonstrate how it works.

Now, convince me that the multiplier (mixer) waveform would be
different depending on which input was the carrier or modulation.

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.

I give up. What you've done is created a word salad. That's where
you have a mess of buzzwords, shredded together, mixed with some
window dressing, and served in a manner to imply that you have a clue
what you're disgorging. Even the most basic concepts are not sinking
in. You've also ignored multiple suggestions to read some very fine
sources on how RF and modulation works. Open book, insert face, and
come back when you have a clue as to the basics.

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.

Wrong. With AM it's easy. The higher frequency is always the
carrier. Can you give me a diagram or a commonly used communications
system where the reverse might be true? I can't.

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.]

Yawn...

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

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

Don Bowey wrote:

...
You are hearing the effects of the sidebands, not the Carrier.

DUH! And, you only have the sidebands as a result of the
carrier/modulation ...

In a properly designed transmitter the Carrier amplitude does not change
with modulation. I have better tools than FM receivers to prove that fact
and theory agree for AM.

And the time to argue the insignificant ... sharpen that razor blade,
you can then successfully split much narrower hairs ...

JS