: 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. Add that with the clarifier knob requirement of SSB
round table group chat and AM remains popular. 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.
: 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.
:[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...
: 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..? 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.
: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.
: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..?
: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."
: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.
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..?
The desciption and the summary are accurate.
How about you plugging in a similar example and going through it here on
the news group.
: Overmodulation is next week's lesson.
Let's get this one done first...
skipp
http://sonic.ucdavis.edu