Sverre Holm wrote:
I think you have a point here. Removal of one side of the set of sidebands
turns the FM signal into a sort of AM/SSB signal. During transmission,
FM's robustness to impulse noise will be lost.

This would appear to depend on how sharp the skirt of our hypothetical SSB
(really VSB, now) filter is? I.e., at low carrier deviations there's some
AM and therefore it's not _quite_ as robus, whereas at higher carrier
deviations the filter would be nice and flat and look just like regular FM
in terms of amplitude.

After all... in the presense of some AM on regular double side band FM, most
receivers still perform just fine, don't they?

---Joel Kolstad

W7TI wrote:
In the USA, the FCC used to prohibit simultaneous amplitude and
frequency modulation. I did a search of Part 97 rules and I don't see
that exact wording now, but I would still tread lightly in this area.

Sure, I'm not advocating anybody go out and purposely modulate their FM
signals.

Provided all the sidebands are confined to a band no wider than
conventional AM, you probably won't be bothered by Uncle Charlie but
caution is advised.

Indeed.

One interesting commercial system out there is the Motorola C-QUAM
(compatible quadrature amplitude modulation) stereo method, used in the US
for commercial AM stereo broadcastings. Since it has to be backwards
compatible with envelope detector-based AM receivers, the resultant output
is -- I would suggest -- something similar to amplitude modulated phase
modulation! (I think it's actually quite clever...)

---Joel Kolstad

W7TI wrote:
In the USA, the FCC used to prohibit simultaneous amplitude and
frequency modulation. I did a search of Part 97 rules and I don't see
that exact wording now, but I would still tread lightly in this area.

Sure, I'm not advocating anybody go out and purposely modulate their FM
signals.

Provided all the sidebands are confined to a band no wider than
conventional AM, you probably won't be bothered by Uncle Charlie but
caution is advised.

Indeed.

One interesting commercial system out there is the Motorola C-QUAM
(compatible quadrature amplitude modulation) stereo method, used in the US
for commercial AM stereo broadcastings. Since it has to be backwards
compatible with envelope detector-based AM receivers, the resultant output
is -- I would suggest -- something similar to amplitude modulated phase
modulation! (I think it's actually quite clever...)

---Joel Kolstad

In article , W7TI
writes:

On Wed, 22 Oct 2003 06:52:37 -0700, "Joel Kolstad"
wrote:

After all... in the presense of some AM on regular double side band FM, most
receivers still perform just fine, don't they?
_________________________________________________ ________

In the USA, the FCC used to prohibit simultaneous amplitude and
frequency modulation. I did a search of Part 97 rules and I don't see
that exact wording now, but I would still tread lightly in this area.
Provided all the sidebands are confined to a band no wider than
conventional AM, you probably won't be bothered by Uncle Charlie but
caution is advised.
--
Bill, W7TI

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.

A general problem with understanding the concept is the simplicity
of the explanations of AM in today's amateur radio. The mathematical
representations of all modulations have been known and distributed in
text books for decades...my introduction to that was "Electronic
Designer's Handbook by Landee, Davis, Albrecht, McGraw-Hill 1957,
Section 5. Those who can follow the series expressions in a
summation formula, study it, will understand how a phasing-type SSB
modulator and demodulator can work. It is much harder to look at the
expressions and "see" FM or PM; Hewlett-Packard's Agilent site has
a neat little animated Java display that may help some on that.

Filter-type SSB from AM is almost intuitive when the AM spectrum is
shown. That is easy to comprehend...once all accept that the content
of each AM sideband has the same information. (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) FM and PM
sidebands are definitely NOT easy to visualize since their individual
amplitudes and phases change depending on modulation index and
modulating frequency. There isn't any corresponding similarity of
FM and PM to AM for the repetition of sidebands' information when
looking at the spectral content.

What Slater was discussing in that January 1977 HR article was what
a group of researchers had already been doing in the early 1970s to
see if there were alternatives to SSB-like frequency multiplexing in
multi-channel circuits. Part of that investigation was to get around
some of the patents still existing on frequency multiplexing via single
sideband techniques (pioneered first on long-distance telephony, by
the way). Another part was to simplify (if possible) the circuitry
involved when carrying a LOT of channels. Equipent of 3 to 4 decades
ago was a lot bulkier than it is now for non-digital multiplexing. The
"narrowband" necessities of working in small-bandspace amateur bands
was not a prime criteria for that research.

Slater explained much of the above in that article and didn't claim any
exciting narrowband results of previous art. The (mislabeled in my
opinion) "single-sideband FM" technique of combining FM and AM
is simply a DIFFERENT way to communicate information.

A truly different way of modulation exists in everyone's telephone line
modem that can send/receive up to 56 Kilobits/Sec in a bandwidth of
only 3 KHz. That is a combination of AM and PM. That isn't intuitive
to AM-oriented minds and there still exist arguments in newsgroups
that such high rates "aren't possible!" :-) Yet most of us POTS users
with computers regularly get 33 to 56 KBPS rates over 2.5 to 3.0 KHz
bandwidth telephone circuits.

I've not seen much on that "single-sideband FM" stuff in the professional
literature after 1980. Based on what was published in the 1970s, it was
an interesting technique but did not come up with any advantages for
commercial or military adoption or much further work. I think it does
show that old paradigms aren't always worth four nickels and that, truly,
thinking outside the box might come up with something new and useful.

Just some comments from
Len Anderson
retired (from regular hours) electronic engineer person

In article , W7TI
writes:

On Wed, 22 Oct 2003 06:52:37 -0700, "Joel Kolstad"
wrote:

After all... in the presense of some AM on regular double side band FM, most
receivers still perform just fine, don't they?
_________________________________________________ ________

In the USA, the FCC used to prohibit simultaneous amplitude and
frequency modulation. I did a search of Part 97 rules and I don't see
that exact wording now, but I would still tread lightly in this area.
Provided all the sidebands are confined to a band no wider than
conventional AM, you probably won't be bothered by Uncle Charlie but
caution is advised.
--
Bill, W7TI

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.

A general problem with understanding the concept is the simplicity
of the explanations of AM in today's amateur radio. The mathematical
representations of all modulations have been known and distributed in
text books for decades...my introduction to that was "Electronic
Designer's Handbook by Landee, Davis, Albrecht, McGraw-Hill 1957,
Section 5. Those who can follow the series expressions in a
summation formula, study it, will understand how a phasing-type SSB
modulator and demodulator can work. It is much harder to look at the
expressions and "see" FM or PM; Hewlett-Packard's Agilent site has
a neat little animated Java display that may help some on that.

Filter-type SSB from AM is almost intuitive when the AM spectrum is
shown. That is easy to comprehend...once all accept that the content
of each AM sideband has the same information. (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) FM and PM
sidebands are definitely NOT easy to visualize since their individual
amplitudes and phases change depending on modulation index and
modulating frequency. There isn't any corresponding similarity of
FM and PM to AM for the repetition of sidebands' information when
looking at the spectral content.

What Slater was discussing in that January 1977 HR article was what
a group of researchers had already been doing in the early 1970s to
see if there were alternatives to SSB-like frequency multiplexing in
multi-channel circuits. Part of that investigation was to get around
some of the patents still existing on frequency multiplexing via single
sideband techniques (pioneered first on long-distance telephony, by
the way). Another part was to simplify (if possible) the circuitry
involved when carrying a LOT of channels. Equipent of 3 to 4 decades
ago was a lot bulkier than it is now for non-digital multiplexing. The
"narrowband" necessities of working in small-bandspace amateur bands
was not a prime criteria for that research.

Slater explained much of the above in that article and didn't claim any
exciting narrowband results of previous art. The (mislabeled in my
opinion) "single-sideband FM" technique of combining FM and AM
is simply a DIFFERENT way to communicate information.

A truly different way of modulation exists in everyone's telephone line
modem that can send/receive up to 56 Kilobits/Sec in a bandwidth of
only 3 KHz. That is a combination of AM and PM. That isn't intuitive
to AM-oriented minds and there still exist arguments in newsgroups
that such high rates "aren't possible!" :-) Yet most of us POTS users
with computers regularly get 33 to 56 KBPS rates over 2.5 to 3.0 KHz
bandwidth telephone circuits.

I've not seen much on that "single-sideband FM" stuff in the professional
literature after 1980. Based on what was published in the 1970s, it was
an interesting technique but did not come up with any advantages for
commercial or military adoption or much further work. I think it does
show that old paradigms aren't always worth four nickels and that, truly,
thinking outside the box might come up with something new and useful.

Just some comments from
Len Anderson
retired (from regular hours) electronic engineer person

Avery Fineman wrote:
There isn't any corresponding similarity of
FM and PM to AM for the repetition of sidebands' information when
looking at the spectral content.

Umm... last I looked the spectrum of FM and PM was symmetrical about the
carrier frequency? (Well, the lower sideband is 180 degrees out of phase
with the upper, but that's true of AM as well.) Looking at a single sine
wave input to an FM or phase modulator, this comes about from the Bessel
function expansion of the sidetones and J-n(x)=-Jn(x)?

I know you're far more experienced in this area than I am, however, so I'll
let you explain what I'm misinterpreting here!

---Joel Kolstad

Avery Fineman wrote:
There isn't any corresponding similarity of
FM and PM to AM for the repetition of sidebands' information when
looking at the spectral content.

Umm... last I looked the spectrum of FM and PM was symmetrical about the
carrier frequency? (Well, the lower sideband is 180 degrees out of phase
with the upper, but that's true of AM as well.) Looking at a single sine
wave input to an FM or phase modulator, this comes about from the Bessel
function expansion of the sidetones and J-n(x)=-Jn(x)?

I know you're far more experienced in this area than I am, however, so I'll
let you explain what I'm misinterpreting here!

---Joel Kolstad

In article , "Joel Kolstad"
writes:

Avery Fineman wrote:
There isn't any corresponding similarity of
FM and PM to AM for the repetition of sidebands' information when
looking at the spectral content.

Umm... last I looked the spectrum of FM and PM was symmetrical about the
carrier frequency? (Well, the lower sideband is 180 degrees out of phase
with the upper, but that's true of AM as well.) Looking at a single sine
wave input to an FM or phase modulator, this comes about from the Bessel
function expansion of the sidetones and J-n(x)=-Jn(x)?

Yes. More or less.

I know you're far more experienced in this area than I am, however, so I'll
let you explain what I'm misinterpreting here!

Noooo...I'm not going to. About a million subjective years ago I had to
slog through a solution and series expansion with the only "help" I got
being a suggestion to use Bessel Functions of the First Kind.

In doing so - AND thinking about it in the process - I learned quite a
bit about the math AND the modulation process. Very useful later on.
ALL learning takes place in one's own noggin...doesn't matter whether
one is in a formal class or alone being "lectured" by print on paper
through the eyeballs.

Over on the Agilent website, I would suggest downloading their free
Application Note 150-1. That is really a subtle selling thing for their
very fine spectrum analyzers but it is also a darn good treatise on
modulation and modulation spectra for all the basic types. It should
(unless altered there) include that nice little animated display of
sidebands versus modulation index. I've always admired those H-P
appnotes, valuing most as nice little tutorials on specialized subjects.

Richard Slater in the mentioned January '77 HR article was trying to
explain a combination of FM and AM. In order to get a proper "feel"
for that (in my opinion), one needs the experience of juggling those
series terms in the expanded equation form. There IS one hint and
that is the not-quite symmetry (in numeric values) of FM and PM
spectra as compared to AM spectra. True "single-sideband" has a
possibility only on true symmetry. FM and PM spectra, by
themselves, don't have that symmetry in the expanded form. I'm
not going to discuss that one since it should be apparent.

If you want some source code on calculating the numeric values of
Bessel Functions of the First Kind, I'll be happy to post it here under
some thread. It's short and not complicated and a #$%^!!! faster than
slugging through 5-place tables with slide rule and/or four-function
mechanical calculator. Been there, done too much of that. Computers
aren't just for chat rooms, are very nice for numeric calculations of the
large kind. :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , "Joel Kolstad"
writes:

Avery Fineman wrote:
There isn't any corresponding similarity of
FM and PM to AM for the repetition of sidebands' information when
looking at the spectral content.

Umm... last I looked the spectrum of FM and PM was symmetrical about the
carrier frequency? (Well, the lower sideband is 180 degrees out of phase
with the upper, but that's true of AM as well.) Looking at a single sine
wave input to an FM or phase modulator, this comes about from the Bessel
function expansion of the sidetones and J-n(x)=-Jn(x)?

Yes. More or less.

I know you're far more experienced in this area than I am, however, so I'll
let you explain what I'm misinterpreting here!

Noooo...I'm not going to. About a million subjective years ago I had to
slog through a solution and series expansion with the only "help" I got
being a suggestion to use Bessel Functions of the First Kind.

In doing so - AND thinking about it in the process - I learned quite a
bit about the math AND the modulation process. Very useful later on.
ALL learning takes place in one's own noggin...doesn't matter whether
one is in a formal class or alone being "lectured" by print on paper
through the eyeballs.

Over on the Agilent website, I would suggest downloading their free
Application Note 150-1. That is really a subtle selling thing for their
very fine spectrum analyzers but it is also a darn good treatise on
modulation and modulation spectra for all the basic types. It should
(unless altered there) include that nice little animated display of
sidebands versus modulation index. I've always admired those H-P
appnotes, valuing most as nice little tutorials on specialized subjects.

Richard Slater in the mentioned January '77 HR article was trying to
explain a combination of FM and AM. In order to get a proper "feel"
for that (in my opinion), one needs the experience of juggling those
series terms in the expanded equation form. There IS one hint and
that is the not-quite symmetry (in numeric values) of FM and PM
spectra as compared to AM spectra. True "single-sideband" has a
possibility only on true symmetry. FM and PM spectra, by
themselves, don't have that symmetry in the expanded form. I'm
not going to discuss that one since it should be apparent.

If you want some source code on calculating the numeric values of
Bessel Functions of the First Kind, I'll be happy to post it here under
some thread. It's short and not complicated and a #$%^!!! faster than
slugging through 5-place tables with slide rule and/or four-function
mechanical calculator. Been there, done too much of that. Computers
aren't just for chat rooms, are very nice for numeric calculations of the
large kind. :-)

Len Anderson
retired (from regular hours) electronic engineer person

Sometimes I really get curious and want to know about something.

I haven't seen the Ham Radio article, but I'm thinking if the whole
idea had any merit it would be a popular mode by now.

Bruce-

It has been about 35 years since I had a class in school where SSB-FM was
discussed. I recall that if you derive the equations for both AM and FM SSB,
they are identical for practical purposes if the FM signal has low deviation
(low modulation index?).

Looking at Two Meter FM, the deviation typically peaks at about 5 KHz. If you
listen to your local repeater with an SSB rig such as the IC-706, it will be
obvious that it isn't a clean signal! However, a 3 KHz deviation FM signal on
HF (below 29 MHz) will sound much cleaner when tuned as SSB, and you may not
notice it isn't AM-SSB.

With this in mind, consider that AM-SSB and FM-SSB might just be two ways to
generate an SSB signal, assuming you use a filter to eliminate the carrier and
other sideband.

By the way, an IC-706, especially one with the TCXO, often has a more accurate
frequency read-out than a typical Two Meter rig. Therefore you can use it to
check a repeater's frequency by tuning it as if it were an SSB station while
someone is speaking. It is easy enough to check the IC-706 against WWV on HF.

73, Fred, K4DII