AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
 

In article ,
Don Bowey wrote:

On 7/6/07 12:15 PM, in article
, "isw"
wrote:

In article ,
Don Bowey wrote:

On 7/6/07 9:36 AM, in article
, "isw"
wrote:

In article ,
Don Bowey wrote:

On 7/5/07 10:27 PM, in article ,
"Ron Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/5/07 12:00 AM, in article
,
"Ron Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/4/07 8:42 PM, in article
,
"Ron
Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/4/07 10:16 AM, in article
,
"Ron Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/4/07 7:52 AM, in article
,
"Ron
Baker, Pluralitas!" wrote:

snip


cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b])

Basically: multiplying two sine waves is
the same as adding the (half amplitude)
sum and difference frequencies.

No, they aren't the same at all, they only appear to be the
same
before
they are examined. The two sidebands will not have the correct
phase
relationship.

What do you mean? What is the "correct"
relationship?


One could, temporarily, mistake the added combination for a full
carrier
with independent sidebands, however.




(For sines it is
sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b])
= 0.5 * (sin[a-b+90degrees] -
sin[a+b+90degrees])
= 0.5 * (sin[a-b+90degrees] +
sin[a+b-90degrees])
)

--
rb





When AM is correctly accomplished (a single voiceband signal is
modulated

The questions I posed were not about AM. The
subject could have been viewed as DSB but that
wasn't the specific intent either.

What was the subject of your question?

Copying from my original post:

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?
What would it look like on a spectrum analyzer?

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?
What would that look like on a spectrum analyzer?




So the first (1) is an AM question and the second (2) is a non-AM
question......

What is the difference between AM and DSB?




AM is a process. DSB (double sideband), with carrier, is it's most
simple
result. DSB without carrier (suppressed carrier dsb) requires using, at
least, a balanced mixer as the AM multiplier.

And requires, for proper reception, that a carrier be recreated at the
receiver which has not only the amplitude of the original,

There is no need at all to match the carrier amplitude of the original
signal. You can use an excessively high carrier injection amplitude with
no
detrimental affect, but if the injected carrier is too little, the
demodulated signal will be over modulated and sound distorted.

but also its exact phase.

Exact, not required. The closer the better, however.

Well, OK, the phase must at least bear a constant relationship to the
one that created the signal. If you inject a carrier that has a
quadrature relationship to the one that created the DSB signal, the
output will be PM (phase modulation). In between zero and 90 degrees,
the output is a combination of the two. If the injected carrier is not
at precisely the proper frequency, the phase will roll around and the
output will be unintelligible.

Not unintelligible.... Donald Duckish.

I think you are confusing *single* sideband, for which that is correct,
and *double* sideband (which we were discussing), for which it is not
true.

On a more practical side, however, most receiver filters for ssb will
essentially remove one sideband if there are two, and can attenuate a
carrier so the local product detector can do it's job resulting in improved
receiving conditions. But this is more advanced than the Ops questions.

Doing it that way will work, but it's not "fair", because you are not
actually demodulating a DSB signal (which was the subject of the
discussion).

Isaac

AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
 

In article ,
Roy Lewallen wrote:

Ron Baker, Pluralitas! wrote:

What is the difference between AM and DSB?

The two actually describe different properties, so a signal can be be
AM, DSB, neither, or both.

And here we run into some trouble between technical correctness and
common usage.

DSB stands for Double SideBand. Although I suppose an FM signal could be
called DSB because it has two *sets* of sidebands

Um, actually, it has a lot more than that. A carrier FM modulated by a
single sine wave has an infinite number of sidebands. If the modulating
signal is more complex, then things get really complicated.

Isaac

AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
 

"isw" wrote in message
...
In article ,
"Ron Baker, Pluralitas!" wrote:

"John Fields" wrote in message
...
On Thu, 5 Jul 2007 00:00:45 -0700, "Ron Baker, Pluralitas!"

snip


When AM is correctly accomplished (a single voiceband signal is
modulated

The questions I posed were not about AM. The
subject could have been viewed as DSB but that
wasn't the specific intent either.

What was the subject of your question?

Copying from my original post:

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?
What would it look like on a spectrum analyzer?

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?
What would that look like on a spectrum analyzer?

---
The first example is amplitude modulation precisely _because_ of the

Is there multiplication in DSB? (double sideband)

Yes, and in fact, that multiplication referred to above creates a
DSB-suppressed-carrier signal. To get "real" AM, you need to add back
the carrier *at the proper phase*.

So does the multiplication in the first example really make
it amplitude modulation?


FWIW, if you do the multiplication and then add back a carrier which is
in quadrature (90 degrees) to the one you started with, what you get is
phase modulation, a "close relative" of FM, and indistinguishable from
it for the most part.

A true DSB-suppressed carrier signal is rather difficult to receive
precisely because of the absolute phase requirement; tuning a receiver
to the right frequency isn't sufficient -- the phase has to match, too,
and that's really difficult without some sort of reference.

A SSB-suppressed carrier signal is a lot simpler to detect because an
error in the frequency of the regenerated carrier merely produces a
similar error in the frequency of the detected audio (the well-known
"Donald Duck" effect).

Isaac

AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-low carrier frequency
 

"Tommy Tootles" wrote in message
t...

Tommy Tootles wrote:

Uh, John...respectfully, I have to wonder just who is on drugs.

The original poster *ASKED* about *DSB* vs. AM

YOU *ANSWERED* about *SSB*. Here is the correct answer...

There are two broad types of DSB (double sideband) transmission:

DSB-RC and DSB-SC, meaning BOTH sidebands are transmitted, but with
either a (R)educed (C)arrier or a (S)urpressed (C)arrier. AM sends
both sidebands and full carrier.

Hope that answers the OP's question

John Smith I wrote:

Yeah, you just discovered that for all intents and purposes double
sideband is am, and suppressed carrier is just like suppressed
carrier am?

Oh well, better late than never ...

JS

What *I* discovered is -not- the point. And for all intents and purposes,
"AM" and DSB are two distinct (but certainly related) things. Different
hardware to create (balanced modulator for DSB vs high level plate
modulation for 'classic' AM), more power required for AM and finally, back
in the day, the FCC had -different- emission designators for AM vs DSB.
Now, if they were the same, why would you think the FCC gave
them -different- emission designators?

You make good, relevant points there.


What IS the point is:

1) The original poster asked a question about "x".

2) You gave a half-assed answer to "y".

And then, you had the bare faced gall to accuse the original poster of
being on drugs!

Look at the good news--even though you gave a partially wrong answer to a
question that wasn't even asked, you at least resolved the issue of which
of the two of you is on drugs... ;-)


I would agree with the above also, but don't
wish to be provocative. ;)

AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
 

Tommy Tootles wrote:

[chit]

Hmmm, why be a half-assed-idiot when you can be a full fledged one? I
see your point ...

Point is, DSB IS AM, you can receive it on any am receiver, get a life,
get off drugs and certainly get off the news groups, you are ill suited
to be here ...

JS

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

"isw" wrote in message
...
In article ,
"Ron Baker, Pluralitas!" wrote:

"isw" wrote in message
...
In article ,
"Ron Baker, Pluralitas!" wrote:

"isw" wrote in message
...
In article ,
"Ron Baker, Pluralitas!" wrote:

snip


While it might not be obvious, the two cases I
described are basically identical. And this
situation occurs in real life, i.e. in radio signals,
oceanography, and guitar tuning.

The beat you hear during guitar tuning is not modulation; there
is
no
non-linear process involved (i.e. no multiplication).

Isaac

In short, the human auditory system is not linear.
It has a finite resolution bandwidth. It can't resolve
two tones separted by a few Hertz as two separate tones.
(But if they are separted by 100 Hz they can easily
be separated without hearing a beat.)

Two tones 100 Hz apart may or may not be perceived separately;
depends
on a lot of other factors. MP3 encoding, for example, depends on the
ear's (very predictable) inability to discern tones "nearby" to
other,
louder ones.

I'll remember that the next time I'm tuning
an MP3 guitar.


The same affect can be seen on a spectrum analyzer.
Give it two frequencies separated by 1 Hz. Set the
resolution bandwidth to 10 Hz. You'll see the peak
rise and fall at 1 Hz.

Yup. And the spectrum analyzer is (hopefully) a very linear system,
producing no intermodulation of its own.

Isaac

What does a spectrum analyzer use to arive at
amplitude values? An envelope detector?
Is that linear?

I'm sure there's more than one way to do it, but I feel certain that
any

Which of them is linear?

A well-designed filter running into a bolometer would be. You can make
the filter narrow enough to respond to only one frequency component at

Any real spectrum analyzer has a lower limit
to its resolution bandwidth, does it not?
The resolution bandwidth of the human ear is non-zero
and not really adjustable, is it not?

the time, and a bolometer just turns the signal power into heat; nothing
nonlinear there...

Really?
You said you are a physicist/engineer.
What does "linear" mean?

AM electromagnetic waves: 20 KHzmodulationfrequencyonanastronomically-low carrier frequency
 

On 7/6/07 8:21 PM, in article
, "isw"
wrote:

In article ,
Don Bowey wrote:

On 7/6/07 12:15 PM, in article
, "isw"
wrote:

In article ,
Don Bowey wrote:

On 7/6/07 9:36 AM, in article
, "isw"
wrote:

In article ,
Don Bowey wrote:

On 7/5/07 10:27 PM, in article ,
"Ron Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/5/07 12:00 AM, in article
,
"Ron Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/4/07 8:42 PM, in article
,
"Ron
Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/4/07 10:16 AM, in article
,
"Ron Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/4/07 7:52 AM, in article
,
"Ron
Baker, Pluralitas!" wrote:

snip


cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b])

Basically: multiplying two sine waves is
the same as adding the (half amplitude)
sum and difference frequencies.

No, they aren't the same at all, they only appear to be the
same
before
they are examined. The two sidebands will not have the correct
phase
relationship.

What do you mean? What is the "correct"
relationship?


One could, temporarily, mistake the added combination for a full
carrier
with independent sidebands, however.




(For sines it is
sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b])
= 0.5 * (sin[a-b+90degrees] -
sin[a+b+90degrees])
= 0.5 * (sin[a-b+90degrees] +
sin[a+b-90degrees])
)

--
rb





When AM is correctly accomplished (a single voiceband signal is
modulated

The questions I posed were not about AM. The
subject could have been viewed as DSB but that
wasn't the specific intent either.

What was the subject of your question?

Copying from my original post:

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?
What would it look like on a spectrum analyzer?

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?
What would that look like on a spectrum analyzer?




So the first (1) is an AM question and the second (2) is a non-AM
question......

What is the difference between AM and DSB?




AM is a process. DSB (double sideband), with carrier, is it's most
simple
result. DSB without carrier (suppressed carrier dsb) requires using, at
least, a balanced mixer as the AM multiplier.

And requires, for proper reception, that a carrier be recreated at the
receiver which has not only the amplitude of the original,

There is no need at all to match the carrier amplitude of the original
signal. You can use an excessively high carrier injection amplitude with
no
detrimental affect, but if the injected carrier is too little, the
demodulated signal will be over modulated and sound distorted.

but also its exact phase.

Exact, not required. The closer the better, however.

Well, OK, the phase must at least bear a constant relationship to the
one that created the signal. If you inject a carrier that has a
quadrature relationship to the one that created the DSB signal, the
output will be PM (phase modulation). In between zero and 90 degrees,
the output is a combination of the two. If the injected carrier is not
at precisely the proper frequency, the phase will roll around and the
output will be unintelligible.

Not unintelligible.... Donald Duckish.

I think you are confusing *single* sideband, for which that is correct,
and *double* sideband (which we were discussing), for which it is not
true.

What do you propose the term be for the output of a slightly de-tuned
demodulator of a DSB sans carrier, signal?


On a more practical side, however, most receiver filters for ssb will
essentially remove one sideband if there are two, and can attenuate a
carrier so the local product detector can do it's job resulting in improved
receiving conditions. But this is more advanced than the Ops questions.

Doing it that way will work, but it's not "fair", because you are not
actually demodulating a DSB signal (which was the subject of the
discussion).

I don't believe the OP stated whether the DSB signal was with or without
carrier. If without carrier, demodulation is certainly called for. If with
carrier, it hardly merits discussion.


Isaac

AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-low carrier frequency
 

On 7/6/07 7:15 PM, in article
, "Tommy Tootles"
wrote:


Tommy Tootles wrote:

Uh, John...respectfully, I have to wonder just who is on drugs.

The original poster *ASKED* about *DSB* vs. AM

YOU *ANSWERED* about *SSB*. Here is the correct answer...

There are two broad types of DSB (double sideband) transmission:

DSB-RC and DSB-SC, meaning BOTH sidebands are transmitted, but with
either a (R)educed (C)arrier or a (S)urpressed (C)arrier. AM sends
both sidebands and full carrier.

Hope that answers the OP's question

John Smith I wrote:

Yeah, you just discovered that for all intents and purposes double
sideband is am, and suppressed carrier is just like suppressed
carrier am?

Oh well, better late than never ...

JS

What *I* discovered is -not- the point. And for all intents and
purposes, "AM" and DSB are two distinct (but certainly related) things
Different hardware to create (balanced modulator for DSB vs high level
plate modulation for 'classic' AM), more power required for AM and
finally, back in the day, the FCC had -different- emission designators
for AM vs DSB. Now, if they were the same, why would you think the FCC
gave them -different- emission designators?


You are confusing FCC use codes and technical processes. Do you believe the
FCC Designator of "J" for ssbsc says HOW to do it. Not for an instant.


What IS the point is:

1) The original poster asked a question about "x".

2) You gave a half-assed answer to "y".

And then, you had the bare faced gall to accuse the original poster of
being on drugs!

Look at the good news--even though you gave a partially wrong answer to
a question that wasn't even asked, you at least resolved the issue of
which of the two of you is on drugs... ;-)

AM electromagnetic waves: 20 KHz modulationfrequencyonanastronomically-lowcarrier frequency
 

isw wrote:
In article ,
Roy Lewallen wrote:
. . .
DSB stands for Double SideBand. Although I suppose an FM signal could be
called DSB because it has two *sets* of sidebands

Um, actually, it has a lot more than that. A carrier FM modulated by a
single sine wave has an infinite number of sidebands. If the modulating
signal is more complex, then things get really complicated.

Sometimes it's difficult to communicate. A "set" can consist of more
than one. In the case of FM, each set includes an infinite number,
although only a limited number contain a significant amount of energy.
The remainder can be ignored without any substantial degradation of
received signal quality. This is true regardless of the complexity of
the modulating signal.

Roy Lewallen, W7EL

AM electromagnetic waves: 20 KHz modulation frequencyonanastronomically-lowcarrier frequency
 

John 'Half-way' Smith I wrote:

Point is, DSB IS AM, you can receive it on any am receiver,

Well, another of your half-assed answers. You can receive *DSB-RC* on
any AM receiver because the carrier, although reduced, allows reception
via a simple envelope detector. On the other hand, DSB-SC requires a
product detector, a coherent detector or a Costas Loop, detectors NOT
available on "any" AM receiver. So, yet another "half-an-answer" on your
part.

get off drugs and certainly get off the news groups, you are ill suited
to be here ...

A person asks about "a", *you* give them an answer to "b", then accuse
-them- of being on drugs and say -they- are ill-suited to be here. May I
suggest that you look in the mirror if you are concerned about
suitability...

Your thought processes and (lack of) logic seem quite odd. Odd enough to
question who the drug user might be.