In , Skipp has regular no decafe fake stuff
wrote:

: Frank Gilliland wrote:
: I don't think it's a matter of the adjustment of one knob, since people
: seem to get their kicks out of having lots of knobs on their radios. I
: think it's more about the cost of the radios. You can pick up an AM rig
: at any flea market for pennies; but a working SSB rig, new -or- used
: (that hasn't been butchered), will cost you a few bills.

AM vs SSB operation for the average evening arm chair talker (not living
in a congested area) is probably going to be based a lot on simplicity and
fidelity. The reduced bandwidth of an SSB signal is not as plesant to the
ear for some people.

SSB has the same audio bandwidth as AM, but SSB has less noise. For fidelity,
SSB has AM beat.

Add that with the clarifier knob requirement of SSB
round table group chat and AM remains popular.

I haven't had to move my clarifier in quite a while, mainly because most of the
people I talk to are using radios that haven't been modified.

One must consider the
practical part of radio operation after they've spent the money.

:Modulation percentage & duty cycle.
: Duty cycle is irrelevant since there is no modulation percentage to be
: measured when the radio isn't transmitting.

Hard to have one without the other... all the given examples were of a
transmitted signal.

Duty cycle is the ratio of transmit time to receive time. Modulation percentage
doesn't use receive time as a factor.

: I took the peak-to-average modulation ratio from the ARRL handbook (as
: well as several other textbooks). Take up your argument with it's author.

There is no argument, but many reference values are thrown out by various
texts based on many qualifiers. Said qualifiers should probably be
mentioned in various examples. Older texts I've seen often throw out the
20% number.

Power microphones, audio processors, modulation limiters... things that change
the peak-to-average modulation ratio... all will be discussed soon.

:[cut and paste a little bit of good theory]
:With 100-percent sine-wave modulation, a transmitter produces 1.5
:units of RF power.

: ...."units"?

Yep, when no specific description is used, units work very well. Kind of
like the unit circle often described in mathematics "with a radius of 1."
Should be rather intuitive to most people...

You might have said that the carrier power is the base unit.

: The additional 0.5 unit of power is furnished by the
:modulator and is distributed equally between the two sidebands. This AM
:transmitter is compared with an SSB transmitter rated at 0.5 unit of
:peak-envelope power (PEP).

: If the "additional 0.5 unit of power" is distributed equally between the two
: sidebands, don't you mean 0.25 unit for a single sideband?

Same thing isn't it..?

That depends: what's one half of 0.5?

wait a minute... you used "unit" Frank... see
how well that works. :-)

:Many of these rec radio cb technical posts fail to mention the source of
:the additional power which is furnished by the modulator.
: I didn't. Read my post again.

No one said you did... though as stated "many" people have.

Then how is it relevant to this discussion?

:Most people prefer to trade the "wasted power" for the simplicity of AM
:operation. Kind of the SUV of radio thing... just lacking the dam cell
:phone planted in your ear as you drive along.

: And I prefer to believe that "most people" are uneducated as to the
: benefits of SSB, which is why I wrote that post.

Many people have SSB mode and prefer the simplicity of AM operation. "Life
is box of chocolatte." Sometimes the technical candy is a hard chew.

I didn't say they are Gumps, I said they are uneducated about the benefits of
SSB. And I should rephrase that: "Many CBers are UNDER-educated about the
benefits of SSB."

:When the RF signal is demodulated in the AM receiver an audio voltage
:develops which is equivalent to the sum of the upper- and lower-sideband
:voltages, in this case 1 unit of voltage. This voltage represents the
:output from a diode detector as normally used for AM reception. Such
:detection is called coherent detection because the voltages of the two
:sidebands are added in the detector.

: Holy Smoked Oysters, Skip! That's called "envelope detection" and has
: nothing to do with sidebands! And the "coherer detector" was an ancient
: method of detection
: that was used long before tubes, even before galena crystals! It used iron
: filings that magnetized and 'cohered' to each other under modulated RF currents,
: changing the overall resistance with the modulation. You are WAY, WAY out in
: yonder pasture with THAT one, Skip.

For the example, compare the described coherent detection to envelope
detection. In the classic example are they not similar..?

No, they aren't similar at all, because I have never heard of a detection scheme
where the "voltages of the two sidebands are added in the detector". Care to
reference that one?

Time for another lesson: You can look at AM in two ways. One way is in the
frequency domain, with a carrier of constant amplitude and the modulation
carried in the sidebands. The other way is in the amplitude domain, in which the
carrier varies in amplitude according to the modulation (which is where the term
"Amplitude Modulation" originated). Envelope detection works in the amplitude
domain by passing the rectified RF or IF signal through a low-pass filter. And
in case you didn't notice, a diode detector blocks half the modulation power!

:When the RF signal is demodulated in the SSB receiver, an audio voltage
:of 0.7 unit develops which is equivalent to the transmitted
:upper-sideband signal. If a broadband noise level is chosen as 0.1 unit
:of voltage per 6 kc bandwidth, the AM bandwidth, the same noise level is
:equal to 0.07 unit of voltage per 3 kc bandwidth, the SSB bandwidth.

: A bit obtuse, but ok....

The actual word you should have used is "accurate."

The description is accurate in fact but not in reason.

:These values represent the same noise power level per kc of bandwidth,

: Wrong. Noise voltage level is NOT noise power level, the latter being the sum of
: all the noise within the bandwidth. Narrowing the bandwidth does not reduce the
: noise voltage level but it DOES reduce the noise power level, and it does so in
: direct proportion to the bandwidth. IOW, cut the bandwidth in half and you cut
: the noise power level in half.
: snip faulty explanation based on your lack of understanding

Convenient that you cut out the entire example... no one wrote that
noise voltage is noise power... notice the word "represent" Frank.

All right, if you really want:

These values represent the same noise power level per kc of bandwidth,
that is, 0.12 divided by 6 is equal to 0.072 divided by 3.

Where did you get the values of 0.12 and 0.072? Regardless,

0.12 / 6 = 0.02
0.072 / 3 = 0.024
0.02 0.024

The s/n ratio
for the AM system is 20 log s/n in terms of voltage, or 20 dB. For the
SSB system the s/n ratio is also 20 dB.

Again, where did you get your values of 0.12 and 0.072?

Time for ANOTHER lesson: The intelligibility of an audio signal is defined by
the signal-to-noise ratio of the audio, which is done by measuring the POWER of
the signal and noise, NOT just their voltage. Why? Because sound requires POWER.
Simple, huh? Also, when determining the S/N ratio at the RF input of a receiver,
the signal and noise are measured as VOLTAGE because the input impedance is
common to both.

Therefore the 0.5 power unit of
rated PEP for the SSB transmitter produces the same signal
intelligibility as the 1 power unit of rated carrier power for the AM
transmitter .

Your "1 power unit of rated carrier power" doesn't carry any intelligence. But I
know what you are trying to say, and you're still wrong. Your detection-adder
scheme doesn't work here because, even if such a detector existed, the RF noise
would be detected by the same process, negating the effect you are claiming
actually occurs.

In summary it can be stated that, under ideal propagating conditions but
in the presence of broadband noise,

....which is a contradition in terms...

an SSB signal and an AM signal provide
equal s/n ratios at the receiver if the total sideband power contained in
each of the signals is equal.

Only with your sideband-adding detector.

This means that, to perform under these
conditions as well as an SSB transmitter of given PEP rating, an AM
transmitter requires twice that figure in carrier power rating.

Even if that were true (and it isn't), SSB is still more efficient than AM.

Also notice the example has values worked through to demonstrate the
signal intelligibility. Are any of those values or the end result
summary wrong Frank..?

Your values are not "worked through". It's like you pulled them out of thin air.
Where did you get your values of 0.12 and 0.072?

The desciption and the summary are accurate.

How about you plugging in a similar example and going through it here on
the news group.

How about you learning the concepts before making invalid examples? How about
assigning proper labels to your arbitrary values instead of generic "units"? How
about not skipping steps to hide your mathematical mistakes?

: Overmodulation is next week's lesson.

Let's get this one done first...

As far as I'm concerned, it's done. The only problem here is that you don't
fully understand the concepts involved. Demonstrate that you have learned
something and I'll move on.





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