[AMRadio] AMRadio Digest, Vol 152, Issue 10


Vic Mukal tvictor at attglobal.net
Thu Sep 29 23:02:22 EDT 2016


Don,

I would also like to thank you for submitting such an interesting technical
article.

Tom
WB2STR

On Thu, Sep 29, 2016 at 2:37 PM, <amradio-request at mailman.qth.net> wrote:

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> Today's Topics:
>
>    1. The Physical Reality of Sidebands in the AM signal
>       (Donald Chester)
>    2. Re: FCC's AM power (Nick England)
>    3. Re: The Physical Reality of Sidebands in the AM signal
>       (Oliver Steiner)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 29 Sep 2016 12:50:17 -0500
> From: "Donald Chester" <k4kyv at charter.net>
> To: <amradio at mailman.qth.net>
> Subject: [AMRadio] The Physical Reality of Sidebands in the AM signal
> Message-ID: <004701d21a79$f0d19e00$d274da00$@charter.net>
> Content-Type: text/plain;       charset="us-ascii"
>
>
> >From the beginnings of radiotelephony there has been a question whether
> sidebands exist as physical reality or only in the mathematics of
> modulation
> theory.  In the early 20's this was a hotly debated topic, with a noted
> group of British engineers maintaining that sidebands existed only in the
> mathematics, while an equally well-remembered group of American engineers
> argued that sidebands do, in fact physically exist.
>
> Today, the issue seems settled once and for all.  We can tune our
> modern-day
> highly selective receivers through double-sideband and single-sideband
> voice
> signals, and tune in upper or lower sideband, and even adjust the
> selectivity to the point that we can tune in the carrier minus the
> sidebands.  Nearly everyone accepts the notion that sidebands do indeed
> exist physically...  or do they?
>
> Maybe it's a matter of how we observe the signal, and our result is
> modified
> by our measuring techniques. Those who have studied quantum mechanics will
> recall the Heisenberg uncertainty Principle, which states that it is
> impossible to know both the position (physical location) and velocity
> (speed
> and direction) of a particle at the same time, along with the related
> "Observer Effect", which states that you cannot observe a system without
> changing something in the system. In the following thought experiment, we
> take this to an analogy with an amplitude modulated radio signal.
>
> Imagine a cw transmitter equipped with an electronic keyer.  Also imagine
> that there is no shaping circuitry, so that the carrier is instantly
> switched between full output and zero output. Such a signal can be expected
> to generate extremely broad key clicks above and below the fundamental
> frequency because of the sharp corners of the keying waveform.  Set the
> keying speed up to max, and send a series of dits.  If the keyer is
> adjusted
> properly, the dits and spaces will be of equal length, identical to a full
> carrier AM signal 100 percent modulated by a perfect square wave.
>
> Suppose the keyer is adjusted to send, say, 20 dits per second when the
> "dit" paddle is held down. The result is a 20 Hz square-wave-modulated AM
> signal.  Now turn the speed up. If the keyer has the capability, run it up
> to 100 dits per second.  If you tune in the signal using a receiver with
> very narrow selectivity (100 Hz or less, easily achievable using today's
> technology), you can actually tune in the carrier, and then as you move the
> dial slightly you can tune in sideband components 100, 300, 500 Hz, etc.
> removed from the carrier frequency. A square wave consists of a fundamental
> frequency plus an infinite series of odd harmonics of diminishing
> amplitude.
> Theoretically you would hear carrier components spaced every 200 Hz
> throughout the spectrum.  In a practical case, due to the finite noise
> floor, the diminishing amplitude of the sideband components and selectivity
> of the tuned circuits in the transmitter tank circuit and antenna itself,
> these sideband components eventually become inaudibly buried in the
> background noise as the receiver is tuned away from the carrier frequency.
>
> Suppose we now gradually slow down the keyer.  As we change to lower keying
> speed, it takes more and more selectivity to discriminate between carrier
> and sideband components, as the modulation frequency becomes lower and the
> sideband components become spaced more closely together. Let's observe what
> happens when we slow the dit rate down to 10 dits per second. Now the
> fundamental modulation frequency is 10 Hz, and we can hear sideband
> components at 10 Hz, 30 Hz, 50 Hz, 70 Hz removed from the carrier,
> continuing above and below the carrier frequency at intervals of 20 Hz
> until
> we reach a point  where the signals disappear into the background noise.
> In
> order to distinguish individual sideband components, we need selectivity on
> the order of 10 Hz, which is possible if we use resonant i.f. selectivity
> filters with extremely high "Q".  This can be accomplished using crystal
> filters, regenerative amplifiers or even conventional L-C tuned circuits if
> we carefully design the components to have high enough Q.
>
> As we achieve extreme selectivity with these high Q resonant circuits, we
> observe a sometimes annoying characteristic familiarly known as "ringing."
> This ringing effect is due to the "flywheel effect" of a tuned circuit, the
> same "flywheel effect" that allows a class-C tube type final or class-E
> solid state final to generate a harmonic-free sinewave rf carrier waveform.
> The selective rf tank circuit stores energy which is re-released to fill in
> missing parts of the sinewave, thus filtering out the harmonics inherent to
> operation of these classes of amplifier.  CW operators are very aware of
> the
> ringing effect of very narrow receiving filters, which can make the dits
> and
> dahs of high speed CW run together, causing the signal to be just as
> difficult to read with the narrow filter in line, as the same CW signal
> would be with a wider filter, even one that admits harmful adjacent channel
> interference.  Kind of a damned if you do, damned if you don't scenario.
>
> Now, let's continue with our thought experiment, taking our example of code
> speed and selectivity to absurdity.  We can slow down our keyer to a
> microscopic fraction of a Hertz, to the point where each dit is six months
> long, and the space between dits is also six months long.  In effect, we
> are
> transmitting an unmodulated carrier for six months, then shutting down the
> transmitter for six months. But still, this is only a matter of the degree
> of code speed; the signal waveform is still identical to the AM transmitter
> tone modulated with a perfect square wave, but whose frequency is one cycle
> per year, or 3.17 X (10 to the -8) Hz.  That means that in theory, the
> steady uninterrupted carrier is still being transmitted, along with a
> series
> of sideband components spaced every 6.34 X (10 to the -8) Hz.
>
> Now, carriers spaced every 6.34 X (10 to the -8) Hz apart are inarguably
> VERY close together, to the point that building a filter capable of
> separating them would likely be of complexity on the order of a successful
> expedition to Mars, but still theoretically possible. Let us assume we are
> able to build such a filter.  We would undoubtedly have to resort to
> superconductivity in the tuned circuits, requiring components cooled to
> near
> absolute zero, and thoroughly shield every rf carrying conductor to prevent
> radiation loss, but here we are talking about something hypothetical,
> without the practical restraints of cost, construction time and
> availability
> of material.  Anyway, let us just assume we were able to successfully build
> the required selectivity filter.
>
> The receiver would indeed be able to discriminate between sidebands and
> carrier of the one cycle/year or 3.17 X (10 to the -8) Hz modulated AM
> signal, identical to a CW transmitter with carrier on for six months and
> off
> for six months.  So how can we detect a steady carrier while the
> transmitter
> is shut off for six months?  The answer lies in our receiver.  In order to
> achieve high enough selectivity to separate carrier and sideband components
> at such a low modulating frequency and close spacing, the Q of the tuned
> circuit would have to be so high that the flywheel effect, or ringing of
> the
> filter, would maintain the missing RF carrier during the six-month key-up
> period.
>
> This takes us back to the longstanding debate over the reality of
> sidebands.
> If we use a wideband receiver such as a crystal set with little or no
> front-end selectivity, we can indeed think of the AM signal precisely as a
> steady carrier that varies in amplitude in step with the modulating
> frequency.  This is always the case if the total bandwidth of the signal is
> negligible compared to the selectivity of the receiver.  Once we achieve
> selectivity of the same order as the bandwidth of the signal, which has
> been
> the norm for practical receivers dating from the late 1900's up to the
> present, reception of the signal behaves according to the principle of a
> steady carrier with distinctly observable upper and lower sidebands.  The
> "holes" in the carrier at 100% negative modulation are inaudible due to the
> flywheel effect of the tuned circuits, even though those same "holes" may
> be
> observable on the envelope pattern of an oscilloscope.
>
> An oscilloscope set up for envelope pattern, with the deflection plates
> coupled directly to a sample of the transmitter's output, is a wideband
> device much like a crystal set. It allows us to physically observe the AM
> signal as a carrier of varying amplitude. A spectrum analyser on the other
> hand, is an instrument of high selectivity, namely a selective receiver
> programmed to sweep back and forth across a predetermined band of spectrum
> while visually displaying the amplitude of the signal falling into its
> passband at each instant. It clearly displays distinct upper and lower
> sidebands with a steady carrier in between.
>
> Furthermore, it has often been observed that the envelope pattern of a
> signal as displayed from a scope connected to the i.f. output of a distant
> receiver can be quite different from what is  seen on a monitor scope at
> the
> transmitter site.  This is yet another example of how the pattern is
> altered
> (distorted) by the selective components of the receiver.
>
> In conclusion, there is no correct yes or no answer to the age-old question
> whether or not sidebands are physical reality, or exist only in the
> mathematics of modulation theory. It all depends on how you physically
> observe the signal.  Sidebands physically exist only if you use an
> instrument selective enough to observe them. Putting it another way, their
> existence depends on whether we observe the signal in the time domain or
> the
> frequency domain. Remember the Heisenberg Uncertainty Principle and the
> associated Observer Effect?
>
> Don k4kyv
>
>
>
> ------------------------------
>
> Message: 2
> Date: Thu, 29 Sep 2016 14:13:14 -0400
> From: Nick England <navy.radio at gmail.com>
> To: Donald Chester <k4kyv at charter.net>
> Cc: Discussion of AM Radio in the Amateur Service
>         <amradio at mailman.qth.net>
> Subject: Re: [AMRadio] FCC's AM power
> Message-ID:
>         <CAB55hNcfJFKPY=ZN+iTj3HXzwNV59itmXOyNwkX-
> iJtz2OGTUw at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> Don writes:
> "We all know that an AM signal does not consist of a carrier varying up and
> down in step with the audio, but a steady carrier and two sidebands, all
> existing independently of each other."
>
> Cool! If they are existing *independently* of each other this means I can
> pull the VFO tube out of my AM transmitter so the carrier disappears but
> the sidebands will still be there - amazing! And if I change the VFO
> frequency then the sidebands don't change frequency? Far out! And if the
> upper sideband exists independently of the lower sideband, then I can
> change the audio input frequency to move one sideband and the other one
> won't move? Equally amazing!
>
> This message is displayed on your screen as a carrier (average gray level)
> plus a whole bunch of 2D sidebands in the spatial frequency domain. And if
> those things were *independent* you wouldn't be reading this......
>
> Nick England K4NYW
> www.navy-radio.com
>
>
> ------------------------------
>
> Message: 3
> Date: Thu, 29 Sep 2016 14:36:42 -0400
> From: Oliver Steiner <steinerviolinist at gmail.com>
> To: Donald Chester <k4kyv at charter.net>
> Cc: amradio at mailman.qth.net
> Subject: Re: [AMRadio] The Physical Reality of Sidebands in the AM
>         signal
> Message-ID:
>         <CAEnXyFAP1snf0fxN9003hGGLGZ0j+UEVOARL6znzcOw2Yj88FA at mail.
> gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> Don,
>
> Thank you for this very informative and beautifully written contribution.
>
> Ollie
> W2QXR
>
> On 9/29/16, Donald Chester <k4kyv at charter.net> wrote:
> >
> > From the beginnings of radiotelephony there has been a question whether
> > sidebands exist as physical reality or only in the mathematics of
> > modulation
> > theory.  In the early 20's this was a hotly debated topic, with a noted
> > group of British engineers maintaining that sidebands existed only in the
> > mathematics, while an equally well-remembered group of American engineers
> > argued that sidebands do, in fact physically exist.
> >
> > Today, the issue seems settled once and for all.  We can tune our
> > modern-day
> > highly selective receivers through double-sideband and single-sideband
> > voice
> > signals, and tune in upper or lower sideband, and even adjust the
> > selectivity to the point that we can tune in the carrier minus the
> > sidebands.  Nearly everyone accepts the notion that sidebands do indeed
> > exist physically...  or do they?
> >
> > Maybe it's a matter of how we observe the signal, and our result is
> > modified
> > by our measuring techniques. Those who have studied quantum mechanics
> will
> > recall the Heisenberg uncertainty Principle, which states that it is
> > impossible to know both the position (physical location) and velocity
> > (speed
> > and direction) of a particle at the same time, along with the related
> > "Observer Effect", which states that you cannot observe a system without
> > changing something in the system. In the following thought experiment, we
> > take this to an analogy with an amplitude modulated radio signal.
> >
> > Imagine a cw transmitter equipped with an electronic keyer.  Also imagine
> > that there is no shaping circuitry, so that the carrier is instantly
> > switched between full output and zero output. Such a signal can be
> expected
> > to generate extremely broad key clicks above and below the fundamental
> > frequency because of the sharp corners of the keying waveform.  Set the
> > keying speed up to max, and send a series of dits.  If the keyer is
> > adjusted
> > properly, the dits and spaces will be of equal length, identical to a
> full
> > carrier AM signal 100 percent modulated by a perfect square wave.
> >
> > Suppose the keyer is adjusted to send, say, 20 dits per second when the
> > "dit" paddle is held down. The result is a 20 Hz square-wave-modulated AM
> > signal.  Now turn the speed up. If the keyer has the capability, run it
> up
> > to 100 dits per second.  If you tune in the signal using a receiver with
> > very narrow selectivity (100 Hz or less, easily achievable using today's
> > technology), you can actually tune in the carrier, and then as you move
> the
> > dial slightly you can tune in sideband components 100, 300, 500 Hz, etc.
> > removed from the carrier frequency. A square wave consists of a
> fundamental
> > frequency plus an infinite series of odd harmonics of diminishing
> > amplitude.
> > Theoretically you would hear carrier components spaced every 200 Hz
> > throughout the spectrum.  In a practical case, due to the finite noise
> > floor, the diminishing amplitude of the sideband components and
> selectivity
> > of the tuned circuits in the transmitter tank circuit and antenna itself,
> > these sideband components eventually become inaudibly buried in the
> > background noise as the receiver is tuned away from the carrier
> frequency.
> >
> > Suppose we now gradually slow down the keyer.  As we change to lower
> keying
> > speed, it takes more and more selectivity to discriminate between carrier
> > and sideband components, as the modulation frequency becomes lower and
> the
> > sideband components become spaced more closely together. Let's observe
> what
> > happens when we slow the dit rate down to 10 dits per second. Now the
> > fundamental modulation frequency is 10 Hz, and we can hear sideband
> > components at 10 Hz, 30 Hz, 50 Hz, 70 Hz removed from the carrier,
> > continuing above and below the carrier frequency at intervals of 20 Hz
> > until
> > we reach a point  where the signals disappear into the background noise.
> > In
> > order to distinguish individual sideband components, we need selectivity
> on
> > the order of 10 Hz, which is possible if we use resonant i.f. selectivity
> > filters with extremely high "Q".  This can be accomplished using crystal
> > filters, regenerative amplifiers or even conventional L-C tuned circuits
> if
> > we carefully design the components to have high enough Q.
> >
> > As we achieve extreme selectivity with these high Q resonant circuits, we
> > observe a sometimes annoying characteristic familiarly known as
> "ringing."
> > This ringing effect is due to the "flywheel effect" of a tuned circuit,
> the
> > same "flywheel effect" that allows a class-C tube type final or class-E
> > solid state final to generate a harmonic-free sinewave rf carrier
> waveform.
> > The selective rf tank circuit stores energy which is re-released to fill
> in
> > missing parts of the sinewave, thus filtering out the harmonics inherent
> to
> > operation of these classes of amplifier.  CW operators are very aware of
> > the
> > ringing effect of very narrow receiving filters, which can make the dits
> > and
> > dahs of high speed CW run together, causing the signal to be just as
> > difficult to read with the narrow filter in line, as the same CW signal
> > would be with a wider filter, even one that admits harmful adjacent
> channel
> > interference.  Kind of a damned if you do, damned if you don't scenario.
> >
> > Now, let's continue with our thought experiment, taking our example of
> code
> > speed and selectivity to absurdity.  We can slow down our keyer to a
> > microscopic fraction of a Hertz, to the point where each dit is six
> months
> > long, and the space between dits is also six months long.  In effect, we
> > are
> > transmitting an unmodulated carrier for six months, then shutting down
> the
> > transmitter for six months. But still, this is only a matter of the
> degree
> > of code speed; the signal waveform is still identical to the AM
> transmitter
> > tone modulated with a perfect square wave, but whose frequency is one
> cycle
> > per year, or 3.17 X (10 to the -8) Hz.  That means that in theory, the
> > steady uninterrupted carrier is still being transmitted, along with a
> > series
> > of sideband components spaced every 6.34 X (10 to the -8) Hz.
> >
> > Now, carriers spaced every 6.34 X (10 to the -8) Hz apart are inarguably
> > VERY close together, to the point that building a filter capable of
> > separating them would likely be of complexity on the order of a
> successful
> > expedition to Mars, but still theoretically possible. Let us assume we
> are
> > able to build such a filter.  We would undoubtedly have to resort to
> > superconductivity in the tuned circuits, requiring components cooled to
> > near
> > absolute zero, and thoroughly shield every rf carrying conductor to
> prevent
> > radiation loss, but here we are talking about something hypothetical,
> > without the practical restraints of cost, construction time and
> > availability
> > of material.  Anyway, let us just assume we were able to successfully
> build
> > the required selectivity filter.
> >
> > The receiver would indeed be able to discriminate between sidebands and
> > carrier of the one cycle/year or 3.17 X (10 to the -8) Hz modulated AM
> > signal, identical to a CW transmitter with carrier on for six months and
> > off
> > for six months.  So how can we detect a steady carrier while the
> > transmitter
> > is shut off for six months?  The answer lies in our receiver.  In order
> to
> > achieve high enough selectivity to separate carrier and sideband
> components
> > at such a low modulating frequency and close spacing, the Q of the tuned
> > circuit would have to be so high that the flywheel effect, or ringing of
> > the
> > filter, would maintain the missing RF carrier during the six-month key-up
> > period.
> >
> > This takes us back to the longstanding debate over the reality of
> > sidebands.
> > If we use a wideband receiver such as a crystal set with little or no
> > front-end selectivity, we can indeed think of the AM signal precisely as
> a
> > steady carrier that varies in amplitude in step with the modulating
> > frequency.  This is always the case if the total bandwidth of the signal
> is
> > negligible compared to the selectivity of the receiver.  Once we achieve
> > selectivity of the same order as the bandwidth of the signal, which has
> > been
> > the norm for practical receivers dating from the late 1900's up to the
> > present, reception of the signal behaves according to the principle of a
> > steady carrier with distinctly observable upper and lower sidebands.  The
> > "holes" in the carrier at 100% negative modulation are inaudible due to
> the
> > flywheel effect of the tuned circuits, even though those same "holes" may
> > be
> > observable on the envelope pattern of an oscilloscope.
> >
> > An oscilloscope set up for envelope pattern, with the deflection plates
> > coupled directly to a sample of the transmitter's output, is a wideband
> > device much like a crystal set. It allows us to physically observe the AM
> > signal as a carrier of varying amplitude. A spectrum analyser on the
> other
> > hand, is an instrument of high selectivity, namely a selective receiver
> > programmed to sweep back and forth across a predetermined band of
> spectrum
> > while visually displaying the amplitude of the signal falling into its
> > passband at each instant. It clearly displays distinct upper and lower
> > sidebands with a steady carrier in between.
> >
> > Furthermore, it has often been observed that the envelope pattern of a
> > signal as displayed from a scope connected to the i.f. output of a
> distant
> > receiver can be quite different from what is  seen on a monitor scope at
> > the
> > transmitter site.  This is yet another example of how the pattern is
> > altered
> > (distorted) by the selective components of the receiver.
> >
> > In conclusion, there is no correct yes or no answer to the age-old
> question
> > whether or not sidebands are physical reality, or exist only in the
> > mathematics of modulation theory. It all depends on how you physically
> > observe the signal.  Sidebands physically exist only if you use an
> > instrument selective enough to observe them. Putting it another way,
> their
> > existence depends on whether we observe the signal in the time domain or
> > the
> > frequency domain. Remember the Heisenberg Uncertainty Principle and the
> > associated Observer Effect?
> >
> > Don k4kyv
> >
> > ______________________________________________________________
> > Our Main Website: http://www.amfone.net
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> >
>
>
> --
> http://oliversteiner.com
>
>
> ------------------------------
>
> Subject: Digest Footer
>
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> ------------------------------
>
> End of AMRadio Digest, Vol 152, Issue 10
> ****************************************
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