In , Skipp
wrote:
: Frank Gilliland wrote:
: SSB has the same audio bandwidth as AM, but SSB has less noise. For fidelity,
: SSB has AM beat.
I and others would probably disagree. But to each his own. My AM bandwidth is not the same as my SSB bandwidth. For the
most part, regular AM bandwidth is wider than SSB.
Good grief.... The audio bandwidth (for CB) is the same -- 0.3 to 3 KHz. The RF
bandwidth of AM is more than twice the witch of SSB because it covers from 3 KHz
below to 3 KHz above the carrier, and therefore picks up more than twice the
noise as SSB.
: 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.
No two unmodified radios are on the same exact frequency. Given a group of stock radios, some will be either side of
the assumed channel center.
You don't need the radios to be on the -same exact- frequency, just really
close. And the DEVIATION from that center frequency in an unmodified radio isn't
significant as long as the radio has been properly aligned and maintained. Ever
hear of a 'bell curve'? You and Tnom should get together and form a study group
on that subject. And if you -really- want to pick some nits, you two should also
study some things about temperature compensated crystal oscillators (TCXO's),
PLL frequency synthesis using dual-modulus prescalers, the frequency response of
the human ear and it's variation between different people, the psychology of
sensory perception, etc.
: Duty cycle is the ratio of transmit time to receive time. Modulation percentage
: doesn't use receive time as a factor.
It's more than than just Tx and Rx times...
But receive time has NOTHING to do with modulation percentage! Is that so hard
to understand? Sheesh....!
: Power microphones, audio processors, modulation limiters... things that change
: the peak-to-average modulation ratio... all will be discussed soon.
Opinions will vary quite a bit...
Opinions are like assholes -- everyone has one and they all stink. I don't plan
on discussing opinions. Just facts. And when people have the -facts- they can
make their -own- opinions based on the -facts- instead of relying upon the
uneducated opinions of some wannabe-tech keyclowns.
:: ...."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.
But I did not...
No you didn't. At least we agree on something!
::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?
You want to get the information out... might as well lay the proper foundation.
Nice thought, but you didn't build anything on that foundation!
::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."
No one mentioned Forest Gumps... just playing devils advocate, one should compare the benefits with the trade offs.
And the person that is making such a comparison should have all the facts
available, such as the power and efficiency benefits of SSB over AM. Gee, we
agree on something else!
: 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?
su
http://dj4br.virtualave.net/ssb3e.htm
Next time you plagiarize a ham you better verify his 'facts' first -- here is a
site that does an excellent job of explaining 'coherent detection':
http://www.qsl.net/dj7hs/ccwtheo.htm
BTW, did you notice where he talked about SSB and how the frequency of the
reinserted carrier "may be in error by 100 cycles or more without serious loss
of intelligibility"? That kinda puts the crimp on your "same exact frequency"
complaint.
: 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!
Depends on the detector type... there are more than single diode detectors, even for AM operation.
When was the last time you saw a full-wave AM detector?
: 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
http://dj4br.virtualave.net/ssb3e.htm
God damn, Skip, how dumb can you be? You just copy the stuff without any
comprehension of what it means? His figures of 0.12 and 0.072 are just typos;
they are supposed to be 0.1 squared and 0.07 squared:
0.1^2 = 0.01
0.01 / 6 = 0.00167
0.07^2 = 0.0049
0.0049 / 3 = 0.00163
And they STILL aren't equal because his 'arbitrary' level of noise voltage
wasn't picked arbitrarily -- it was cooked and rounded from the intended result!
Didn't I suggest a long time ago that you should quit relying solely on the
internet for your education? I'm pretty sure I did....
: 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?
http://dj4br.virtualave.net/ssb3e.htm
: 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.
http://dj4br.virtualave.net/ssb3e.htm
"Electronic Communication" by Shrader, McGraw-Hill
"Applied Electronic Comminucation" by Kellejian, SRA
http://www.epanorama.net/documents/a...oisetypes.html
http://www.laidback.org/~daveg/acade...tml/comms.html
http://www.isr.umd.edu/CAAR/papers/m...ysis/model.pdf
Try again, Skip.
: 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.
http://dj4br.virtualave.net/ssb3e.htm
Well, let's see... If the sidebands are added in the detector, then so is the
broadband noise with each sideband. So you have twice the noise bandwidth, and
therefore twice the noise power. above references, but if those are too
complicated try this one:
http://www.geocities.com/w4jbm/noise.html
:In summary it can be stated that, under ideal propagating conditions but
:in the presence of broadband noise,
: ...which is a contradition in terms...
http://dj4br.virtualave.net/ssb3e.htm
That's right, blame it on the person you plagiarized.
: 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.
No one disputes SSB being more efficient, just less practical for the average real world CB radio operator.
http://dj4br.virtualave.net/ssb3e.htm
http://dj4br.virtualave.net/ssb4e.htm
: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?
http://dj4br.virtualave.net/ssb3e.htm
: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?
http://dj4br.virtualave.net/ssb3e.htm
Now you are just being lazy.
:: 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.
http://dj4br.virtualave.net/ssb3e.htm
I like the example description shown, have a look and get back to us with
what ever gets your motor sideways... you might also cc the author if you
have specific questions about his statements.
You might do that yourself to notify him of his mistakes in both theory and
mathematical notation. Then spend a few hours at your public library reading
some -qualified- material on these subjects. You might start with the ARRL's
"Radio Amateur's Handbook", which disagrees in every topic you have referenced
from your source.
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