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Sci.Electronics.Basics -> AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
There are 269 messages in this thread.
You are currently looking at messages 160 to 180.
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Author: iswDate: 12:43 05-07-07
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In article <468cf7f7$0$16602$4c368faf@roadrunner.com>,
"Ron Baker, Pluralitas!" <this@aint.me> wrote:
> "isw" <isw@witzend.com> wrote in message
> news:isw-FB6C92.00093805072007@newsgroups.comcast.net...
> > In article <468bdadd$0$20558$4c368faf@roadrunner.com>,
> > "Ron Baker, Pluralitas!" <this@aint.me> 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
competently designed unit will not add any signals of its own to what it
is being used to analyze.
Isaac
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Author: iswDate: 13:00 05-07-07
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In article <vvup83pjuva65aivk8mq60n75h3hdlcl67@4ax.com>,
John Fields <jfields@austininstruments.com> wrote:
> On Thu, 05 Jul 2007 00:06:02 -0700, isw <isw@witzend.com> wrote:
>
> >In article <850o839ntgabdqke8ogani1s11sc3hmh2i@4ax.com>,
> > John Fields <jfields@austininstruments.com> wrote:
> >
> >> On Wed, 04 Jul 2007 09:11:58 -0700, isw <isw@witzend.com> wrote:
> >>
> >> >In article <468bb3c0$0$24780$4c368faf@roadrunner.com>,
> >> > "Ron Baker, Pluralitas!" <this@aint.me> wrote:
> >>
> >> >> You win. :)
> >> >>
> >> >> When I conceived the problem I was thinking
> >> >> cosines actually. In which case there are no
> >> >> phase shifts to worry about in the result.
> >> >>
> >> >> I also forgot the half amplitude factor.
> >> >>
> >> >> 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).
> >>
> >> ---
> >> That's not true.
> >>
> >> The human ear has a logarithmic amplitude response and the beat note
> >> (the difference frequency) is generated there. The sum frequency is
> >> too, but when unison is achieved it'll be at precisely twice the
> >> frequency of either fundamental and won't be noticed.
> >
> >Now you get to explain why the beat is measurable with instrumentation,
> >and can can be viewed in the waveform of a high-quality recording.
>
> ---
> Simple. The process isn't totally linear, starting with the musical
> instrument itself, so some heterodyning will inevitably occur which
> will be detected by the measuring instrumentation.
That would suggest that there could be "low IM" instruments which would
be very difficult to tune, since they would produce undetectably small
beats; in fact that does not happen. It would also suggest that it would
be difficult or impossible to create beats between two
very-low-distortion signal generators, which is also not the case.
Other than the nonlinearity of the air (which is very small for
"ordinary" SPL, there's no mechanism to cause IM between two different
instruments, although beats are still generated. The beat is simply a
vector summation of two nearly identical signals; no modulation needs to
take place.
Or consider this: At true "zero beat" with the signals exactly 180
degrees out, no energy is avaliable for any non-linear process to act on.
> >Then go on to show why all other multi-frequency-component signals (e.g.
> >a full orchestra) don't produce similar intermodulation effects in ears
> >under normal conditions.
>
> ---
> They do
Well, no, mostly they don't, until you get to really high SPL.
> and why don't you try being a little less of a pompous ass?
Exposing claims to conditions they have difficulty with is a good way to
understand why those claims are invalid -- so long as the claimant
actually explains what's going on, and doesn't just make up answers that
fit the previously stated beliefs.
Isaac
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Author: Jim KelleyDate: 16:48 05-07-07
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John Fields wrote:
> On Wed, 04 Jul 2007 09:11:58 -0700, isw <isw@witzend.com> wrote:
>
>
>>In article <468bb3c0$0$24780$4c368faf@roadrunner.com>,
>>"Ron Baker, Pluralitas!" <this@aint.me> wrote:
>>The beat you hear during guitar tuning is not modulation; there is no
>>non-linear process involved (i.e. no multiplication).
>
>
> ---
> That's not true.
But it is true.
> The human ear has a logarithmic amplitude response and the beat note
> (the difference frequency) is generated there.
The ear does happen to have a logarithmic amplitude response as a
function of frequency, but that has nothing to do with this
phenomenon. (It relates only to the aural sensitivity of the ear at
different frequencies.) What the ear responds to is the sound pressure
wave that results from the superposition of the two waves. The effect
in air is measurable with a microphone as well as by ear. The same
thing can be seen purely electrically in the time domain on an
oscilloscope, and does appear exactly as Ron Baker described in the
frequency domain on a spectrum analyzer.
> The sum frequency is
> too, but when unison is achieved it'll be at precisely twice the
> frequency of either fundamental and won't be noticed.
The ear does not hear the sum of two waves as the sum of the
frequencies, but rather as the sum of their instantaneous amplitudes.
When the pitches are identical, the instantaneous amplitude varies
with time at the fundamental frequency. When they are identical and
in-phase, the instantaneous amplitude varies at the fundamental
frequency with twice the peak amplitude.
When the two pitches are different, the sum of the instantaneous
amplitudes at a fixed point varies with time at a frequency equal to
the difference between pitches. This does have an envelope-like
effect, but it is a different effect than the case of amplitude
modulation. In this case we actually have two pitches, each with
constant amplitude, whereas with AM we have only one pitch, but with
time varying amplitude.
The terms in the trig identity are open to a bit of misinterpretation.
At first glance it does look as though we have a wave sin(a+b) which
is being modulated by a wave sin(a-b). But what we have is a more
complex waveform than a pure sine wave with a modulated amplitude.
There exists no sine wave with a frequency of a+b in the frequency
spectrum of beat modulated sine waves a and b. As has been noted
previously, this is the sum of two waves not the product. I think it
can also help not to inadvertantly switch back and forth from time
domain to frequency domain when thinking about these things.
ac6xg
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Author: John FieldsDate: 19:15 05-07-07
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On Thu, 05 Jul 2007 13:48:04 -0700, Jim Kelley <jwkelley@uci.edu>
wrote:
>John Fields wrote:
>> On Wed, 04 Jul 2007 09:11:58 -0700, isw <isw@witzend.com> wrote:
>>
>>
>>>In article <468bb3c0$0$24780$4c368faf@roadrunner.com>,
>>>"Ron Baker, Pluralitas!" <this@aint.me> wrote:
>
>>>The beat you hear during guitar tuning is not modulation; there is no
>>>non-linear process involved (i.e. no multiplication).
>>
>>
>> ---
>> That's not true.
>
>But it is true.
>
>> The human ear has a logarithmic amplitude response and the beat note
>> (the difference frequency) is generated there.
>
>The ear does happen to have a logarithmic amplitude response as a
>function of frequency, but that has nothing to do with this
>phenomenon.
---
Regardless of the frequency response characteristics of the ear, its
response to amplitude changes _is_ logarithmic.
For instance:
CHANGE APPARENT CHANGE
IN SPL IN LOUDNESS
---------+------------------
3 dB Just noticeable
5 dB Clearly noticeable
10 dB Twice or half as loud
20 dB 4 times or 1/4 as loud
---
>(It relates only to the aural sensitivity of the ear at
>different frequencies.) What the ear responds to is the sound pressure
>wave that results from the superposition of the two waves. The effect
>in air is measurable with a microphone as well as by ear. The same
>thing can be seen purely electrically in the time domain on an
>oscilloscope, and does appear exactly as Ron Baker described in the
>frequency domain on a spectrum analyzer.
>
>> The sum frequency is
>> too, but when unison is achieved it'll be at precisely twice the
>> frequency of either fundamental and won't be noticed.
>
>The ear does not hear the sum of two waves as the sum of the
>frequencies, but rather as the sum of their instantaneous amplitudes.
> When the pitches are identical, the instantaneous amplitude varies
>with time at the fundamental frequency. When they are identical and
>in-phase, the instantaneous amplitude varies at the fundamental
>frequency with twice the peak amplitude.
---
You missed my point, which was that in a mixer (which the ear is,
since its amplitude response is nonlinear) as the two carriers
approach each other the difference frequency will go to zero and the
sum frequency will go to the second harmonic of either carrier,
making it largely appear to vanish into the fundamental.
---
>When the two pitches are different, the sum of the instantaneous
>amplitudes at a fixed point varies with time at a frequency equal to
>the difference between pitches.
---
But the resultant waveform will be distorted and contain additional
spectral components if that summation isn't done linearly. This is
precisely what happens in the ear when equal changes in SPL don't
result in equal outputs to the 8th cranial nerve.
---
>This does have an envelope-like
>effect, but it is a different effect than the case of amplitude
>modulation. In this case we actually have two pitches, each with
>constant amplitude, whereas with AM we have only one pitch, but with
>time varying amplitude.
---
That's not true. In AM we have two pitches, but one is used to
control the amplitude of the other, which generates the sidebands.
---
>The terms in the trig identity are open to a bit of misinterpretation.
> At first glance it does look as though we have a wave sin(a+b) which
>is being modulated by a wave sin(a-b). But what we have is a more
>complex waveform than a pure sine wave with a modulated amplitude.
---
No, it's much simpler since you haven't created the sum and
difference frequencies and placed them in the spectrum.
---
>There exists no sine wave with a frequency of a+b in the frequency
>spectrum of beat modulated sine waves a and b. As has been noted
>previously, this is the sum of two waves not the product.
---
"Beat modulated" ??? LOL, if you're talking about the linear
summation of a couple of sine waves, then there is _no_ modulation
of any type taking place and the instantaneous voltage (or whatever)
out of the system will be the simple algebraic sum of the inputs
times whatever _linear_ gain there is in the system at that instant.
Real modulation requires multiplication, which can be done by mixing
two signals in a nonlinear device and will result in the output of
the original signals and their sum and difference frequencies.
---
>I think it
>can also help not to inadvertantly switch back and forth from time
>domain to frequency domain when thinking about these things.
---
Oh, well...
--
JF
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Author: Rich GriseDate: 19:42 05-07-07
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On Tue, 03 Jul 2007 22:42:20 -0700, isw wrote:
> After you get done talking about modulation and sidebands, somebody
> might want to take a stab at explaining why, if you tune a receiver to
> the second harmonic (or any other harmonic) of a modulated carrier (AM
> or FM; makes no difference), the audio comes out sounding exactly as it
> does if you tune to the fundamental? That is, while the second harmonic
> of the carrier is twice the frequency of the fundamental, the sidebands
> of the second harmonic are *not* located at twice the frequencies of the
> sidebands of the fundamental, but rather precisely as far from the
> second harmonic of the carrier as they are from the fundamental.
Have you ever actually observed this effect?
Thanks,
Rich
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Author: Jim KelleyDate: 21:37 05-07-07
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John Fields wrote:
> You missed my point, which was that in a mixer (which the ear is,
> since its amplitude response is nonlinear) as the two carriers
> approach each other the difference frequency will go to zero and the
> sum frequency will go to the second harmonic of either carrier,
> making it largely appear to vanish into the fundamental.
Hi John -
Given two sources of pure sinusoidal tones whose individual amplitudes
are constant, is it your claim that you have heard the sum of the two
frequencies?
ac6xg
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Author: Keith DysartDate: 22:01 05-07-07
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On Jul 5, 7:15 pm, John Fields <jfie...@austininstruments.com> wrote:
> Regardless of the frequency response characteristics of the ear, its
> response to amplitude changes _is_ logarithmic.
It seems clear that the brain's perception of amplitude changes
is logarithmic. It is not so obvious that this means there
exists a non-linear amplitude response in the ear such that
harmonics are generated.
I suggest the following alternative explanations:
- the nerve signals from the ear to the brain could have a
linear response but the low level driver in the brain
converts it to a logarithmic response for later processing.
- the nerves from the ear could have a logarithmic response
- the AGC which limits the signal applied to the detectors in
the ear by tightening muscles in the bones, could have a
logarithmic response. The cycle by cycle response in the
ear could be linear.
The actual detector (if I recall my physiology correctly)
consists of little hairs that actually detect different
frequencies so that what is presented to the low level
drivers is actually a spectrum, not the sound waveform.
A non-linear amplitude response in these hairs would not
produce inter-mod but would be preceived as non-linear.
It is possible that the eardrum and bones connecting to
the cochlea exhibit a non-linear response and are
capable of generating inter-mod, but this is not
proven just because the system has an apparent logarithmic
response at the point of perception.
Is there other evidence that the ear is non-linear before
separating the signal into its component frequencies and
therefore can generate inter-mod?
> "Beat modulated" ??? LOL, if you're talking about the linear
> summation of a couple of sine waves, then there is _no_ modulation
> of any type taking place and the instantaneous voltage (or whatever)
> out of the system will be the simple algebraic sum of the inputs
> times whatever _linear_ gain there is in the system at that instant.
>
> Real modulation requires multiplication, which can be done by mixing
> two signals in a nonlinear device and will result in the output of
> the original signals and their sum and difference frequencies.
A 4 quadrant multiplier will leave no trace of the original
two frequencies, only the sum and difference will be present
in the spectrum. This could equally well have been generated
by adding the two frequencies present in the spectrum. If
the two frequencies in the spectrum are close, there will
be an observable envelope that will be perceived as the
sound rising and falling in amplitude. There is no need
for a non-linear response for this to occur.
Not that this proves there is not one, but the existence
of the effect does not prove that there is one.
...Keith
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Author: Bob MyersDate: 22:02 05-07-07
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"John Fields" <jfields@austininstruments.com> wrote in message
news:i7pq83t1jau92okmpr3dsuh3fkdj01g3sg@4ax.com...
> You missed my point, which was that in a mixer (which the ear is,
> since its amplitude response is nonlinear) as the two carriers
> approach each other the difference frequency will go to zero and the
> sum frequency will go to the second harmonic of either carrier,
> making it largely appear to vanish into the fundamental.
Sorry, John - while the ear's amplitude response IS nonlinear, it
does not act as a mixer. "Mixing" (multiplication) occurs when
a given nonlinear element (in electronics, a diode or transistor, for
example) is presented with two signals of different frequencies.
But the human ear doesn't work in that manner - there is no single
nonlinear element which is receiving more than one signal.
Frequency discrimination in the ear occurs through the resonant
frequencies of the 20-30,000 fibers which make up the basilar
membrane within the cochlea. Each fiber responds only to those
tones which are at or very near its resonant frequency. While
the response of each fiber to the amplitude of the signal is nonliner,
no mixing occurs because each responds, in essence, only to a
single tone. A model for the hearing process might be 30,000 or
so non-linear meters, each seeing the output of a very narrow-band
bandpass filter covering a specific frequency within the audio
range. There is clearly no mixing, at least as the term is commonly
used in electronics, going on in such a situation, even though there
is non-linearity in some aspect of the system's response.
Audible "beats" are perceived not because there is mixing going on
within the ear, but instead are due to cycles of constructive and
destructive
interference going on in the air between the two original tones.
Bob M.
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Author: iswDate: 00:03 06-07-07
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In article <pan.2007.07.05.23.42.45.964093@example.net>,
Rich Grise <rich@example.net> wrote:
> On Tue, 03 Jul 2007 22:42:20 -0700, isw wrote:
>
> > After you get done talking about modulation and sidebands, somebody
> > might want to take a stab at explaining why, if you tune a receiver to
> > the second harmonic (or any other harmonic) of a modulated carrier (AM
> > or FM; makes no difference), the audio comes out sounding exactly as it
> > does if you tune to the fundamental? That is, while the second harmonic
> > of the carrier is twice the frequency of the fundamental, the sidebands
> > of the second harmonic are *not* located at twice the frequencies of the
> > sidebands of the fundamental, but rather precisely as far from the
> > second harmonic of the carrier as they are from the fundamental.
>
> Have you ever actually observed this effect?
Sure. (In a previous life, I designed AM and FM transmitters for RCA).
Just get a short-wave radio, locate yourself fairly close to a standard
AM transmitter, and tune to the harmonics. you'll find, in every case,
that the audio sounds just the same as if you were listening to the
fundamental.
Works for FM, too, but the situation is somewhat more complex.
Isaac
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Author: iswDate: 00:09 06-07-07
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In article <i7pq83t1jau92okmpr3dsuh3fkdj01g3sg@4ax.com>,
John Fields <jfields@austininstruments.com> wrote:
> On Thu, 05 Jul 2007 13:48:04 -0700, Jim Kelley <jwkelley@uci.edu>
> wrote:
>
> >John Fields wrote:
> >> On Wed, 04 Jul 2007 09:11:58 -0700, isw <isw@witzend.com> wrote:
> >>
> >>
> >>>In article <468bb3c0$0$24780$4c368faf@roadrunner.com>,
> >>>"Ron Baker, Pluralitas!" <this@aint.me> wrote:
> >
> >>>The beat you hear during guitar tuning is not modulation; there is no
> >>>non-linear process involved (i.e. no multiplication).
> >>
> >>
> >> ---
> >> That's not true.
> >
> >But it is true.
> >
> >> The human ear has a logarithmic amplitude response and the beat note
> >> (the difference frequency) is generated there.
> >
> >The ear does happen to have a logarithmic amplitude response as a
> >function of frequency, but that has nothing to do with this
> >phenomenon.
>
> ---
> Regardless of the frequency response characteristics of the ear, its
> response to amplitude changes _is_ logarithmic.
>
> For instance:
>
> CHANGE APPARENT CHANGE
> IN SPL IN LOUDNESS
> ---------+------------------
> 3 dB Just noticeable
>
> 5 dB Clearly noticeable
>
> 10 dB Twice or half as loud
>
> 20 dB 4 times or 1/4 as loud
>
> ---
>
> >(It relates only to the aural sensitivity of the ear at
> >different frequencies.) What the ear responds to is the sound pressure
> >wave that results from the superposition of the two waves. The effect
> >in air is measurable with a microphone as well as by ear. The same
> >thing can be seen purely electrically in the time domain on an
> >oscilloscope, and does appear exactly as Ron Baker described in the
> >frequency domain on a spectrum analyzer.
> >
> >> The sum frequency is
> >> too, but when unison is achieved it'll be at precisely twice the
> >> frequency of either fundamental and won't be noticed.
> >
> >The ear does not hear the sum of two waves as the sum of the
> >frequencies, but rather as the sum of their instantaneous amplitudes.
> > When the pitches are identical, the instantaneous amplitude varies
> >with time at the fundamental frequency. When they are identical and
> >in-phase, the instantaneous amplitude varies at the fundamental
> >frequency with twice the peak amplitude.
>
> ---
> You missed my point, which was that in a mixer (which the ear is,
> since its amplitude response is nonlinear) as the two carriers
> approach each other the difference frequency will go to zero and the
> sum frequency will go to the second harmonic of either carrier,
> making it largely appear to vanish into the fundamental.
> ---
>
> >When the two pitches are different, the sum of the instantaneous
> >amplitudes at a fixed point varies with time at a frequency equal to
> >the difference between pitches.
>
> ---
> But the resultant waveform will be distorted and contain additional
> spectral components if that summation isn't done linearly. This is
> precisely what happens in the ear when equal changes in SPL don't
> result in equal outputs to the 8th cranial nerve.
> ---
>
> >This does have an envelope-like
> >effect, but it is a different effect than the case of amplitude
> >modulation. In this case we actually have two pitches, each with
> >constant amplitude, whereas with AM we have only one pitch, but with
> >time varying amplitude.
>
> ---
> That's not true. In AM we have two pitches, but one is used to
> control the amplitude of the other, which generates the sidebands.
> ---
>
> >The terms in the trig identity are open to a bit of misinterpretation.
> > At first glance it does look as though we have a wave sin(a+b) which
> >is being modulated by a wave sin(a-b). But what we have is a more
> >complex waveform than a pure sine wave with a modulated amplitude.
>
> ---
> No, it's much simpler since you haven't created the sum and
> difference frequencies and placed them in the spectrum.
> ---
>
> >There exists no sine wave with a frequency of a+b in the frequency
> >spectrum of beat modulated sine waves a and b. As has been noted
> >previously, this is the sum of two waves not the product.
>
> ---
> "Beat modulated" ??? LOL, if you're talking about the linear
> summation of a couple of sine waves, then there is _no_ modulation
> of any type taking place and the instantaneous voltage (or whatever)
> out of the system will be the simple algebraic sum of the inputs
> times whatever _linear_ gain there is in the system at that instant.
Absolutely correct. And as that "simple algebraic sum" varies with time,
which it will as the phases of the two signals slide past each other, it
produces the tuning "beat" we've been talking about. Totally linear.
Isaac
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Author: iswDate: 00:12 06-07-07
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In article <f6k7r8$ifb$1@usenet01.boi.hp.com>,
"Bob Myers" <nospamplease@address.invalid> wrote:
> Bob M.
(Personal message; sorry, but e-mail wouldn't work.)
Hi, Bob. It's been a long time since we used to correspond on rec.audio.
Nice to hear from you.
Isaac
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Author: Ron Baker, Pluralitas!Date: 01:01 06-07-07
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"isw" <isw@witzend.com> wrote in message
news:isw-0779A4.09400205072007@newsgroups.comcast.net...
> In article <468cf4d8$0$12241$4c368faf@roadrunner.com>,
> "Ron Baker, Pluralitas!" <this@aint.me> wrote:
>
>> "isw" <isw@witzend.com> wrote in message
>> news:isw-A5E71F.00111305072007@newsgroups.comcast.net...
>> > In article <468bd109$0$31234$4c368faf@roadrunner.com>,
>> > "Ron Baker, Pluralitas!" <this@aint.me> wrote:
>> >
>> >> "isw" <isw@witzend.com> wrote in message
>> >> news:isw-656111.22422003072007@newsgroups.comcast.net...
>> >>
>> >> <snip>
>> >>
>> >> >
>> >> > After you get done talking about modulation and sidebands,
somebody
>> >> > might want to take a stab at explaining why, if you tune a
receiver
>> >> > to
>> >> > the second harmonic (or any other harmonic) of a modulated
carrier
>> >> > (AM
>> >> > or FM; makes no difference), the audio comes out sounding exactly
as
>> >> > it
>> >> > does if you tune to the fundamental? That is, while the second
>> >> > harmonic
>> >> > of the carrier is twice the frequency of the fundamental, the
>> >> > sidebands
>> >> > of the second harmonic are *not* located at twice the frequencies
of
>> >> > the
>> >> > sidebands of the fundamental, but rather precisely as far from
the
>> >> > second harmonic of the carrier as they are from the fundamental.
>> >> >
>> >> > Isaac
>> >>
>> >> Whoa. I thought you were smoking something but
>> >> my curiosity is piqued.
>> >> I tried shortwave stations and heard no harmonics.
>> >> But that could be blamed on propagation.
>> >> There is an AM station here at 1.21 MHz that is s9+20dB.
>> >> Tuned to 2.42 MHz. Nothing. Generally the lowest
>> >> harmonics should be strongest. Then I remembered
>> >> that many types of non-linearity favor odd harmonics.
>> >> Tuned to 3.63 MHz. Holy harmonics, batman.
>> >> There it was and the modulation was not multiplied!
>> >> Voices sounded normal pitch. When music was
>> >> played the pitch was the same on the original and
>> >> the harmonic.
>> >>
>> >> One clue is that the effect comes and goes rather
>> >> abruptly. It seems to switch in and out rather
>> >> than fade in an out. Maybe the coming and going
>> >> is from switching the audio material source?
>> >>
>> >> This is strange. If a signal is multiplied then the sidebands
>> >> should be multiplied too.
>> >> Maybe the carrier generator is generating a
>> >> harmonic and the harmonic is also being modulated
>> >> with the normal audio in the modulator.
>> >> But then that signal would have to make it through
>> >> the power amp and the antenna. Possible, but
>> >> why would it come and go?
>> >> Strange.
>> >
>> > Hint: Modulation is a "rate effect".
>> >
>> > Isaac
>>
>> Please elaborate. I am so eager to hear the
>> explanation.
>
> The sidebands only show up because there is a rate of change of the
> carrier -- amplitude or frequency/phase, depending; they aren't
> separate, stand-alone signals. Since the rate of change of the amplitude
> of the second harmonic is identical to that of the fundamental, the
> sidebands show up the same distance away, not twice as distant.
>
> Isaac
That doesn't explain why the effect would
come and go.
But once again you have surprised me.
Your explanation of the non-multiplied sidebands,
while qualitative and incomplete, is sound.
It looks to me that the tripple frequency sidebands
are there but the basic sidebands dominate.
Especially at lower modulation indexes.
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Author: Ron Baker, Pluralitas!Date: 01:13 06-07-07
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"isw" <isw@witzend.com> wrote in message
news:isw-15D472.09430705072007@newsgroups.comcast.net...
> In article <468cf7f7$0$16602$4c368faf@roadrunner.com>,
> "Ron Baker, Pluralitas!" <this@aint.me> wrote:
>
>> "isw" <isw@witzend.com> wrote in message
>> news:isw-FB6C92.00093805072007@newsgroups.comcast.net...
>> > In article <468bdadd$0$20558$4c368faf@roadrunner.com>,
>> > "Ron Baker, Pluralitas!" <this@aint.me> 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?
> competently designed unit will not add any signals of its own to what it
> is being used to analyze.
>
> Isaac
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Author: Ron Baker, Pluralitas!Date: 01:27 06-07-07
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"Don Bowey" <dbowey@comcast.net> wrote in message
news:C2B25726.6D728%dbowey@comcast.net...
> On 7/5/07 12:00 AM, in article 468c96c3$0$16567$4c368faf@roadrunner.com,
> "Ron Baker, Pluralitas!" <this@aint.me> wrote:
>
>>
>> "Don Bowey" <dbowey@comcast.net> wrote in message
>> news:C2B1DFAF.6D6BD%dbowey@comcast.net...
>>> On 7/4/07 8:42 PM, in article 468c6838$0$4664$4c368faf@roadrunner.com,
>>> "Ron
>>> Baker, Pluralitas!" <this@aint.me> wrote:
>>>
>>>>
>>>> "Don Bowey" <dbowey@comcast.net> wrote in message
>>>> news:C2B16AE5.6D5BC%dbowey@comcast.net...
>>>>> On 7/4/07 10:16 AM, in article
>>>>> 468bd5ad$0$16531$4c368faf@roadrunner.com,
>>>>> "Ron Baker, Pluralitas!" <this@aint.me> wrote:
>>>>>
>>>>>>
>>>>>> "Don Bowey" <dbowey@comcast.net> wrote in
message
>>>>>> news:C2B1129D.6D573%dbowey@comcast.net...
>>>>>>> On 7/4/07 7:52 AM, in article
>>>>>>> 468bb3c0$0$24780$4c368faf@roadrunner.com,
>>>>>>> "Ron
>>>>>>> Baker, Pluralitas!" <this@aint.me> 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?
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Author: Ron Baker, Pluralitas!Date: 01:29 06-07-07
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"John Smith I" <assemblywizard@gmail.com> wrote in message
news:f6ivk2$cl0$2@nnrp.linuxfan.it...
> Ron Baker, Pluralitas! wrote:
> > ...
>> Copying from my original post:
>>
>> Suppose you have a 1 MHz sine wave whose amplitude
>> is multiplied by a 0.1 MHz sine wave.
>> What would it look like on an oscilloscope?
>> What would it look like on a spectrum analyzer?
>>
>> Then suppose you have a 1.1 MHz sine wave added
>> to a 0.9 MHz sine wave.
>> What would that look like on an oscilloscope?
>> What would that look like on a spectrum analyzer?
>>
>>
>>
>
> Lots of BS here ...
>
> The signal ends up looking like a 1Mhz signal contained within the walls
> of the .1Mhz signal ... and simply said, the 1Mhz signal is enclosed in
> the envelope of a .1Mhz signal--the "walls" of this .1Mhz signal being
> referred to as "sidebands."
Is that for both cases?
Where did the 1 MHz component in your
result come from?
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Author: John Smith IDate: 01:53 06-07-07
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Ron Baker, Pluralitas! wrote:
> Where did the 1 MHz component in your
> result come from?
From your original question; hell to get old and experience
Alzheimers', huh?
What, you have never seen rf in a modulation envelope before?
JS
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Author: John Smith IDate: 01:55 06-07-07
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Ron Baker, Pluralitas! wrote:
> Where did the 1 MHz component in your
> result come from?
From your original question; hell to get old and experience
Alzheimers', huh?
What, you have never seen rf in a modulation envelope before?
JS
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Author: Ron Baker, Pluralitas!Date: 02:51 06-07-07
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"John Smith I" <assemblywizard@gmail.com> wrote in message
news:f6klgl$au$1@nnrp.linuxfan.it...
> Ron Baker, Pluralitas! wrote:
>
> > Where did the 1 MHz component in your
> > result come from?
>
> From your original question; hell to get old and experience Alzheimers',
> huh?
Says the fellow who hit the send button twice. :)
>
> What, you have never seen rf in a modulation envelope before?
>
> JS
What is the difference between AM and DSB?
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Author: Brenda AnnDate: 03:15 06-07-07
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"Ron Baker, Pluralitas!" <this@aint.me> wrote in message
news:468de643$0$8986$4c368faf@roadrunner.com...
>
> "John Smith I" <assemblywizard@gmail.com> wrote in message
> news:f6klgl$au$1@nnrp.linuxfan.it...
>> Ron Baker, Pluralitas! wrote:
>>
>> > Where did the 1 MHz component in your
>> > result come from?
>>
>> From your original question; hell to get old and experience Alzheimers',
>> huh?
>
> Says the fellow who hit the send button twice. :)
>
>>
>> What, you have never seen rf in a modulation envelope before?
>>
>> JS
>
> What is the difference between AM and DSB?
>
Both are AM.
Standard AM is DSB with full carrier
SSB with and without carrier/reduced carrier are also both AM.
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Author: Ian JacksonDate: 04:43 06-07-07
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In message <isw-1A3E21.21032905072007@newsgroups.comcast.net>, isw
<isw@witzend.com> writes
>In article <pan.2007.07.05.23.42.45.964093@example.net>,
> Rich Grise <rich@example.net> wrote:
>
>> On Tue, 03 Jul 2007 22:42:20 -0700, isw wrote:
>>
>> > After you get done talking about modulation and sidebands, somebody
>> > might want to take a stab at explaining why, if you tune a receiver to
>> > the second harmonic (or any other harmonic) of a modulated carrier (AM
>> > or FM; makes no difference), the audio comes out sounding exactly as it
>> > does if you tune to the fundamental? That is, while the second harmonic
>> > of the carrier is twice the frequency of the fundamental, the sidebands
>> > of the second harmonic are *not* located at twice the frequencies of the
>> > sidebands of the fundamental, but rather precisely as far from the
>> > second harmonic of the carrier as they are from the fundamental.
>>
>> Have you ever actually observed this effect?
>
>Sure. (In a previous life, I designed AM and FM transmitters for RCA).
>Just get a short-wave radio, locate yourself fairly close to a standard
>AM transmitter, and tune to the harmonics. you'll find, in every case,
>that the audio sounds just the same as if you were listening to the
>fundamental.
>
>Works for FM, too, but the situation is somewhat more complex.
>
>Isaac
Yes, I think I'm missing something obvious here. Let me have another
think (aloud)....
If you FM modulate a 1MHz carrier with a 1kHz tone, you get a spectrum
consisting of a 1MHz carrier in the middle, plus a family of sidebands
harmonically spaced at 1kHz, 2kHz, 3kHz etc (to infinity).
[One obvious difference between the FM spectrum and that of an AM signal
is that the AM spectrum only has sidebands at 1kHz, and the amplitude of
the carrier does not vary with modulation depth. With the FM signal, the
amplitudes of the carrier and each pair of sideband do vary with the
amount of modulation.]
So, if you FM modulate a 1MHz carrier with a 1kHz tone, you get a 1Mhz
carrier and the family of 1kHz 'harmonic' sidebands. Demodulated it, and
you hear a 1kHz tone.
Now double the signal to 2MHz. You might expect the sidebands to appear
at 2, 4, 6kHz etc. However, if you demodulated the signal, you still
hear the original 1kHz tone (which should now be double the amplitude of
the original 1MHz signal). You definitely don't hear 2kHz. This at least
proves that the original 1kHz FM modulation is preserved during the
doubling process.
So, would it be simplistically correct to consider that, during the
doubling process, the original family of 1kHz sidebands also mix with
the new 2MHz carrier, and create a family of 1kHz sidebands centred on
2MHz?
Or, alternatively, does the original family of 1kHz sidebands (on the
1MHz signal) mix with the original 1MHz carrier to produce a family of
baseband 1kHz 'harmonic' signals, and these then mix with the new 2MHz
carrier to create the family of 1kHz sidebands centred on 2MHz?
Or are both equally valid (invalid)?
A possible flaw in my simplistic 'explanations' is that I would have
thought that, while the doubling process occurs as a result of 2nd-order
intermodulation, surely the two-step process in both 'explanations' is
really 4th-order intermodulation?
However, my explanations work equally well (?) for FM and AM.
Am I wrong, or am I wrong?
Ian.
--
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