Along the same line consider that the envelope of an SSB signal has no
direct relationship to the original modulation the way that an AM
signal does.

This is why you can not use RF derived ALC to control the audio stage
of an SSB transmitter the way you can with an AM transmitter.
Or audio clipping that works on AM but does not work the same on SSB.

Transmit a square wave on an AM transmitter and you see a square wave
in the AM envelope. Do the same with an SSB transmitter and you only
see sharp spikes in the envelope.

73
Gary K4FMX


On Thu, 23 Oct 2003 12:08:31 -0700, "Joel Kolstad"
wrote:

Fred McKenzie wrote:
Perhaps that is what I'm remembering. Now, if you use a filter to
eliminate the other sideband, the higher frequency components and the
carrier, don't you have a nearly identical remainder?

At that point I don't think you could tell the difference since there's no
longer any local phase reference (i.e., the carrier) to compare with. I
suppose this is why your SSB-AM rig is able to (somewhat) receive low
frequency (and thereby presumably narrowband) FM broadcasts; this is what
you were saying in your last post, correct?

I think we are in agreement that you can't recover FM modulation with
just an envelope detector

Yes, at least you can't recover a signal that directly corresponds to what
you transmitted. It does appear that you can recover the signal's square,
however, so this approach might be useful for, e.g., remote command
transmissions. (But probably just for the novelty of having said you did
it... since it's probably not much harder to build the slope detector you
describe!)

---Joel

So what you are saying is that the carrier of a modulated signal is
ONLY a frequency domain concept? That would mean that it really does
turn on and off in the time domain at the modulation rate.

73
Gary K4FMX


On Thu, 23 Oct 2003 10:49:46 -0700, Roy Lewallen
wrote:

You have to be careful in what you call the "carrier". As soon as you
start modulating the "carrier", you have more than one frequency
component. At that time, only the component at the frequency of the
original unmodulated signal is called the "carrier". So you have a
modulated RF signal, part of which is the "carrier", and part of which
is sidebands.

General frequency domain analysis makes the assumption that each
frequency component has existed forever and will exist forever. So under
conditions of modulation with a periodic signal, you have three
components: A "carrier", which is not modulated, but a steady, single
frequency, constant amplitude signal; and two sidebands, each of which
is a frequency shifted (and, for the LSB, reversed) replica of the
modulating waveform.

You can take each of these waveforms, add them together in the time
domain, and get the familiar modulated envelope.

So, the short answer is that the carrier, which is a frequency domain
concept, is there even if you're modulating at 0.001 Hz. But to observe
it, you've got to watch for much longer than 1000 seconds. You simply
can't do a meaningful spectrum analysis of a signal in a time that's not
a lot longer than the modulation period.

Roy Lewallen, W7EL

Gary Schafer wrote:
Speaking of AM modulation,, we all know that the carrier amplitude
does not change with modulation. Or does it?

Here is a question that has plagued many for years:
If you have a plate modulated transmitter, the plate voltage will
swing down to zero and up to two times the plate voltage with 100%
modulation. At 100% negative modulation the plate voltage is cutoff
for the instant of the modulation negative peak.

How is the carrier still transmitted during the time there is zero
plate voltage?

If we lower the modulation frequency to say 1 cps or even lower, 1
cycle per minute, then wouldn't the transmitter final be completely
off for half that time and unable to produce any carrier output??

Question is, at what point does the carrier start to be effected?


73
Gary K4FMX

So what you are saying is that the carrier of a modulated signal is
ONLY a frequency domain concept? That would mean that it really does
turn on and off in the time domain at the modulation rate.

73
Gary K4FMX


On Thu, 23 Oct 2003 10:49:46 -0700, Roy Lewallen
wrote:

You have to be careful in what you call the "carrier". As soon as you
start modulating the "carrier", you have more than one frequency
component. At that time, only the component at the frequency of the
original unmodulated signal is called the "carrier". So you have a
modulated RF signal, part of which is the "carrier", and part of which
is sidebands.

General frequency domain analysis makes the assumption that each
frequency component has existed forever and will exist forever. So under
conditions of modulation with a periodic signal, you have three
components: A "carrier", which is not modulated, but a steady, single
frequency, constant amplitude signal; and two sidebands, each of which
is a frequency shifted (and, for the LSB, reversed) replica of the
modulating waveform.

You can take each of these waveforms, add them together in the time
domain, and get the familiar modulated envelope.

So, the short answer is that the carrier, which is a frequency domain
concept, is there even if you're modulating at 0.001 Hz. But to observe
it, you've got to watch for much longer than 1000 seconds. You simply
can't do a meaningful spectrum analysis of a signal in a time that's not
a lot longer than the modulation period.

Roy Lewallen, W7EL

Gary Schafer wrote:
Speaking of AM modulation,, we all know that the carrier amplitude
does not change with modulation. Or does it?

Here is a question that has plagued many for years:
If you have a plate modulated transmitter, the plate voltage will
swing down to zero and up to two times the plate voltage with 100%
modulation. At 100% negative modulation the plate voltage is cutoff
for the instant of the modulation negative peak.

How is the carrier still transmitted during the time there is zero
plate voltage?

If we lower the modulation frequency to say 1 cps or even lower, 1
cycle per minute, then wouldn't the transmitter final be completely
off for half that time and unable to produce any carrier output??

Question is, at what point does the carrier start to be effected?


73
Gary K4FMX

In article , W7TI
writes:

On 22 Oct 2003 20:21:16 GMT, (Avery Fineman) wrote:

(there are still some
long-timers who refuse to accept that the carrier RF energy doesn't
change in AM at less than 100% modulation, heh heh)
_________________________________________________ ________

I still remember the first time I got hold of a really narrowband
receiver and tuned in only the carrier of an AM signal.

I was astonished. That was the most enlightening two or three seconds
in my whole radio career. :-)

Roger that! :-)

The first time I had to really calibrate an FM deviation indicator, I had
to use the "carrier null" technique with a narrow-bandpass detector
(actually a spectrum analyzer). Say WHAT?!? I thought. The
carrier amplitude goes to ZERO?!? Impossible, I thought, "everyone
knows" that an FM carrier "swings from side to side." :-)

Not long after that I got deep into modulation theory and discovered
the how and why of that. Mind-blowing at the time, but it explained
what was going on.

It's a situation where one has to look at either frequency domain or
time domain very hard in order to realize how the two are related.

Len Anderson
retired (from regular hours) electronic engineer person

In article , W7TI
writes:

On 22 Oct 2003 20:21:16 GMT, (Avery Fineman) wrote:

(there are still some
long-timers who refuse to accept that the carrier RF energy doesn't
change in AM at less than 100% modulation, heh heh)
_________________________________________________ ________

I still remember the first time I got hold of a really narrowband
receiver and tuned in only the carrier of an AM signal.

I was astonished. That was the most enlightening two or three seconds
in my whole radio career. :-)

Roger that! :-)

The first time I had to really calibrate an FM deviation indicator, I had
to use the "carrier null" technique with a narrow-bandpass detector
(actually a spectrum analyzer). Say WHAT?!? I thought. The
carrier amplitude goes to ZERO?!? Impossible, I thought, "everyone
knows" that an FM carrier "swings from side to side." :-)

Not long after that I got deep into modulation theory and discovered
the how and why of that. Mind-blowing at the time, but it explained
what was going on.

It's a situation where one has to look at either frequency domain or
time domain very hard in order to realize how the two are related.

Len Anderson
retired (from regular hours) electronic engineer person

In article , Gary Schafer
writes:

Speaking of AM modulation,, we all know that the carrier amplitude
does not change with modulation. Or does it?

Yes and no.

It's a situation of subjective understanding of the basic modulation
formulas which define the amplitude of an "RF" waveform as a
function of TIME [usually denoted as RF voltage "e (t)" meaning the
voltage at any given point in time].

With a REPETITIVE modulation waveform of a single, pure audio
sinewave, AND the modulation percentage LESS than 100%, the
carrier frequency amplitude does indeed remain the same. I put some
words into all-caps for emphasis...those are required definitions for
proof of both the math AND a bench test set-up using a very narrow
bandwidth selective detector.

One example witnessed (outside of formal schooling labs) used an
audio tone of 10 KHz for amplitude modulation of a 1.5 MHz RF stable
continuous wave carrier. With a 100 Hz (approximate) bandwidth
of the detector (multiple-down-conversion receiver), the carrier
frequency amplitude remained constant despite the modulation
percentage changed over 10 to 90 percent. Retuning the detector to
1.49 or 1.51 MHz center frequency, the amplitude of the sidebands
varied in direct proportion to the modulation percentage.

That setup was right according to theory for a REPETITIVE modulation
signal as measured in the FREQUENCY domain.

But, but, but...according to a high-Z scope probe of the modulated RF,
the amplitude was varying! Why? The oscilloscope was just linearly
combining ALL the RF products, the carrier and the two sidebands.
The scope "saw" everything on a broadband basis and the display to
humans was the very SAME RF but in the TIME domain.

But...all the above is for a REPETITVE modulation signal condition.
That's relatively easy to determine mathematically since all that is
or has to be manipulated are the carrier frequency and modulation
frequency and their relative amplitudes. What can get truly hairy
is when the modulation signal is NOT repretitive...such as voice or
music.

Here is a question that has plagued many for years:
If you have a plate modulated transmitter, the plate voltage will
swing down to zero and up to two times the plate voltage with 100%
modulation. At 100% negative modulation the plate voltage is cutoff
for the instant of the modulation negative peak.

How is the carrier still transmitted during the time there is zero
plate voltage?

If we lower the modulation frequency to say 1 cps or even lower, 1
cycle per minute, then wouldn't the transmitter final be completely
off for half that time and unable to produce any carrier output??

I don't blame you for being puzzled...I used to be so for many
years long ago, too. :-)

Most new commercial AM transmitters of today combine the
"modulator" with the power amplifier supply voltage, getting rid of
the old (sometimes mammoth) AF power amplifier in series with
the tube plate supply. Yes, in the TIME domain, the RF power
output does indeed vary at any point in time according to the
modulation. [that still follows the general math formula, "e(t)"]

You can take the modulation frequency and run it as low as
possible. With AM there is no change in total RF amplitude
over frequency (with FM and PM there is). If you've got an
instantaneous time window power meter you can measure it
directly (but ain't no such animal quite yet).

If you set up a FREQUENCY domain test as first described, you
will, indeed, measure NO carrier amplitude change with a very
narrow bandwidth selective detector at any modulation percentage
less than 100% using a REPETITIVE modulation signal.

Actual modulation isn't "repetitive" in the sense that a signal
generator single audio tone is repetitive. What is a truly TERRIBLY
COMPLEX task is both mathematical and practical PROOF of
RF spectral components (frequency domain) versus RF time
domain amplitudes when the modulation is not repetitive. Please
don't go there unless you are a math genius...I wasn't and tried,
got sent to a B. Ford Clinic for a long term. :-)

In a receiver's conventional AM detector, the recovered audio is
a combination of: (1). The diode, already non-linear, is a mixer
that combines carrier and sidebands producing an output that is
the difference of all of them; (2). The diode recovers the time
domain amplitude of the RF, runs it through a low-pass filter to
leave only the audio modulation...and also allows averaging of the
RF signal amplitude over a longer time. Both (1) and (2) are
technically correct.

With a pure SSB signal there is a constant RF amplitude with a
constant-amplitude repetitive modulation signal, exactly as it
would be if the RF output was from a Class C stage. Single
frequency if the modulation signal is a pure audio tone. With a
non-repetitive modulation the total RF power output varies with
the modulation amplitude. The common SSB demodulator
("product detector") is really a MIXER combining the SSB input
with a constant, LOCAL RF carrier ("BFO") with the difference
product output...which recovers the original modulation signal.

Question is, at what point does the carrier start to be effected?

Beyond 100% modulation. The most extreme is a common
radar pulse, very short in time duration, very long (relative) in
repetition time. There's a formula long derived for the amplitude
of the spectra of that, commonly referred to as "Sine x over x"
when spoken. That sets the receiver bandwidth needed to recover
a target return.

I've gotten waist-deep into "matched filter" signals, such as using
a 1 MHz bandwidth filter to recover 1 microSecond RF pulses.
(bandwidth is equivalent to the inverse of on-time of signal, hence
the term "matched" for the filter) Most folks, me included, were
utterly amazed at the filtered RF output envelope when a detector
was tuned off to one side by 1, 2, or 3 MHz. Not at all intuitive.
The math got a bit hairy on that and I just accepted the late Jack
Breckman's explanation (of RCA Camden) since it worked on the
bench as predicted.

It's all a matter of how the observer is observing RF things, time
domain versus frequency domain...and whether the modulation is
repetitive single frequency or multiple, non-repetitive. The math for
a repetitive modulation signal works out as the rule for practical
hardware that has to handle non-repetitive, multi-frequency
modulation signals.

When combining two basic modulation forms, things get so hairy
its got fur all over. So, like someone explain how an ordinary
computer modem can send 56 Kilobits per second over a 3 KHz
bandwidth circuit? :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , Gary Schafer
writes:

Speaking of AM modulation,, we all know that the carrier amplitude
does not change with modulation. Or does it?

Yes and no.

It's a situation of subjective understanding of the basic modulation
formulas which define the amplitude of an "RF" waveform as a
function of TIME [usually denoted as RF voltage "e (t)" meaning the
voltage at any given point in time].

With a REPETITIVE modulation waveform of a single, pure audio
sinewave, AND the modulation percentage LESS than 100%, the
carrier frequency amplitude does indeed remain the same. I put some
words into all-caps for emphasis...those are required definitions for
proof of both the math AND a bench test set-up using a very narrow
bandwidth selective detector.

One example witnessed (outside of formal schooling labs) used an
audio tone of 10 KHz for amplitude modulation of a 1.5 MHz RF stable
continuous wave carrier. With a 100 Hz (approximate) bandwidth
of the detector (multiple-down-conversion receiver), the carrier
frequency amplitude remained constant despite the modulation
percentage changed over 10 to 90 percent. Retuning the detector to
1.49 or 1.51 MHz center frequency, the amplitude of the sidebands
varied in direct proportion to the modulation percentage.

That setup was right according to theory for a REPETITIVE modulation
signal as measured in the FREQUENCY domain.

But, but, but...according to a high-Z scope probe of the modulated RF,
the amplitude was varying! Why? The oscilloscope was just linearly
combining ALL the RF products, the carrier and the two sidebands.
The scope "saw" everything on a broadband basis and the display to
humans was the very SAME RF but in the TIME domain.

But...all the above is for a REPETITVE modulation signal condition.
That's relatively easy to determine mathematically since all that is
or has to be manipulated are the carrier frequency and modulation
frequency and their relative amplitudes. What can get truly hairy
is when the modulation signal is NOT repretitive...such as voice or
music.

Here is a question that has plagued many for years:
If you have a plate modulated transmitter, the plate voltage will
swing down to zero and up to two times the plate voltage with 100%
modulation. At 100% negative modulation the plate voltage is cutoff
for the instant of the modulation negative peak.

How is the carrier still transmitted during the time there is zero
plate voltage?

If we lower the modulation frequency to say 1 cps or even lower, 1
cycle per minute, then wouldn't the transmitter final be completely
off for half that time and unable to produce any carrier output??

I don't blame you for being puzzled...I used to be so for many
years long ago, too. :-)

Most new commercial AM transmitters of today combine the
"modulator" with the power amplifier supply voltage, getting rid of
the old (sometimes mammoth) AF power amplifier in series with
the tube plate supply. Yes, in the TIME domain, the RF power
output does indeed vary at any point in time according to the
modulation. [that still follows the general math formula, "e(t)"]

You can take the modulation frequency and run it as low as
possible. With AM there is no change in total RF amplitude
over frequency (with FM and PM there is). If you've got an
instantaneous time window power meter you can measure it
directly (but ain't no such animal quite yet).

If you set up a FREQUENCY domain test as first described, you
will, indeed, measure NO carrier amplitude change with a very
narrow bandwidth selective detector at any modulation percentage
less than 100% using a REPETITIVE modulation signal.

Actual modulation isn't "repetitive" in the sense that a signal
generator single audio tone is repetitive. What is a truly TERRIBLY
COMPLEX task is both mathematical and practical PROOF of
RF spectral components (frequency domain) versus RF time
domain amplitudes when the modulation is not repetitive. Please
don't go there unless you are a math genius...I wasn't and tried,
got sent to a B. Ford Clinic for a long term. :-)

In a receiver's conventional AM detector, the recovered audio is
a combination of: (1). The diode, already non-linear, is a mixer
that combines carrier and sidebands producing an output that is
the difference of all of them; (2). The diode recovers the time
domain amplitude of the RF, runs it through a low-pass filter to
leave only the audio modulation...and also allows averaging of the
RF signal amplitude over a longer time. Both (1) and (2) are
technically correct.

With a pure SSB signal there is a constant RF amplitude with a
constant-amplitude repetitive modulation signal, exactly as it
would be if the RF output was from a Class C stage. Single
frequency if the modulation signal is a pure audio tone. With a
non-repetitive modulation the total RF power output varies with
the modulation amplitude. The common SSB demodulator
("product detector") is really a MIXER combining the SSB input
with a constant, LOCAL RF carrier ("BFO") with the difference
product output...which recovers the original modulation signal.

Question is, at what point does the carrier start to be effected?

Beyond 100% modulation. The most extreme is a common
radar pulse, very short in time duration, very long (relative) in
repetition time. There's a formula long derived for the amplitude
of the spectra of that, commonly referred to as "Sine x over x"
when spoken. That sets the receiver bandwidth needed to recover
a target return.

I've gotten waist-deep into "matched filter" signals, such as using
a 1 MHz bandwidth filter to recover 1 microSecond RF pulses.
(bandwidth is equivalent to the inverse of on-time of signal, hence
the term "matched" for the filter) Most folks, me included, were
utterly amazed at the filtered RF output envelope when a detector
was tuned off to one side by 1, 2, or 3 MHz. Not at all intuitive.
The math got a bit hairy on that and I just accepted the late Jack
Breckman's explanation (of RCA Camden) since it worked on the
bench as predicted.

It's all a matter of how the observer is observing RF things, time
domain versus frequency domain...and whether the modulation is
repetitive single frequency or multiple, non-repetitive. The math for
a repetitive modulation signal works out as the rule for practical
hardware that has to handle non-repetitive, multi-frequency
modulation signals.

When combining two basic modulation forms, things get so hairy
its got fur all over. So, like someone explain how an ordinary
computer modem can send 56 Kilobits per second over a 3 KHz
bandwidth circuit? :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , Paul Keinanen
writes:

On 22 Oct 2003 20:21:16 GMT, (Avery Fineman)
wrote:

Bill, I just dug out the 1977 issues of HR from storage and looked
the article over. Author Richard Slater (W3EJD) said almost the
same thing at the end of the article on page 15 under "closing
comments." The nomenclatures for different modulations were
formalized by the ITU-R since then but the FCC still doesn't have
anything covering this "single-sideband FM" modulation type for
U. S. amateur radio.

The ITU-R emission designations are quite outdated and many modern
emissions use din commercial and military systems would be designated
as XXX. In each case the X means "none above" in the corresponding
column.

Okay, I won't argue the ITU-R thing since I haven't had the ability
(by working for a subscribing corporation) to access them. I was
going by the "Red Book" information from the U. S. National
Telecommunications and Information Agency (NTIA). Over here
the NTIA regulates government radio use while the U. S. Federal
Communications Commission regulates civil radio use. The
method of specifying modulation type, bandwidth, etc., are all
explained in there and the FCC follows the same nomenclature.

Anyway, why should the amateur radio regulations contain these ITU-R
designations ? Here in Finland, ITU-R emission designations were
removed from amateur radio regulations and exam in 1997 and only band
specific power and bandwidth limits are used. I haven't heard of any
problems due to this decision.

That's a whole other area that, for amateur radio use, can be and has
been argued in rec.radio.amateur.policy.

As far as I'm concerned, and no one has ever proved otherwise,
electrons, fields, and waves all follow the Laws of physics...and they
don't give a @#$%!! about human laws. :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , Paul Keinanen
writes:

On 22 Oct 2003 20:21:16 GMT, (Avery Fineman)
wrote:

Bill, I just dug out the 1977 issues of HR from storage and looked
the article over. Author Richard Slater (W3EJD) said almost the
same thing at the end of the article on page 15 under "closing
comments." The nomenclatures for different modulations were
formalized by the ITU-R since then but the FCC still doesn't have
anything covering this "single-sideband FM" modulation type for
U. S. amateur radio.

The ITU-R emission designations are quite outdated and many modern
emissions use din commercial and military systems would be designated
as XXX. In each case the X means "none above" in the corresponding
column.

Okay, I won't argue the ITU-R thing since I haven't had the ability
(by working for a subscribing corporation) to access them. I was
going by the "Red Book" information from the U. S. National
Telecommunications and Information Agency (NTIA). Over here
the NTIA regulates government radio use while the U. S. Federal
Communications Commission regulates civil radio use. The
method of specifying modulation type, bandwidth, etc., are all
explained in there and the FCC follows the same nomenclature.

Anyway, why should the amateur radio regulations contain these ITU-R
designations ? Here in Finland, ITU-R emission designations were
removed from amateur radio regulations and exam in 1997 and only band
specific power and bandwidth limits are used. I haven't heard of any
problems due to this decision.

That's a whole other area that, for amateur radio use, can be and has
been argued in rec.radio.amateur.policy.

As far as I'm concerned, and no one has ever proved otherwise,
electrons, fields, and waves all follow the Laws of physics...and they
don't give a @#$%!! about human laws. :-)

Len Anderson
retired (from regular hours) electronic engineer person

Gary Schafer wrote:
So what you are saying is that the carrier of a modulated signal is
ONLY a frequency domain concept?

Yes.

That would mean that it really does
turn on and off in the time domain at the modulation rate.


"It" only exists in the frequency domain. Talking about the carrier in
the time domain makes no more sense than talking about the sidebands in
the time domain, or the envelope in the frequency domain.

Roy Lewallen, W7EL