🚀 go-pugleaf

On Sep 27, 6:13 pm, dpl...@radagast.org (Dave Platt) wrote in 
http://groups.google.com/group/uk.tech.digital-tv/msg/118b30e3f36c8b05 :

 > In article <46fc4458$0$16496$4c368...@roadrunner.com>,
 > Green Xenon [Radium] <gluceg...@excite.com> wrote:

 > >It�s possible to downshift the frequencies of an audio signal without
 > >low-pass-filtering or changing the speed at which it is played-back.
 > >Couldn�t the equivalent be done with the temporal and spatial
 > >frequencies of a luminance signal?
 >
 > Once again, no, not enough to matter.  If it was only a matter of 2:1
 > or 10:1, you might be able to do it.  The one-baud scheme you propose
 > is off by a factor of 1,000,000,000,000,...,000 to 1 or so (*lots* of
 > zeros in there).

Would 300:1 work?

300 Hz is the minimum frequency used by telephones and ULF 
[Ultra-Low-Frequency] radios.

ULF radio = frequencies at least 300 Hz but no more than 3,000 Hz.

 > Go do as I said, and google "Shannon Limit".  To sum it up:  there's a
 > hard limit on the amount of information that you can send through a
 > communication channel which has (a) a finite bandwidth, and (2) a
 > finite signal-to-noise ratio.
 >
 > Your goal of trying to pack video-grade information into small gaps in
 > the MW spectrum goes far beyond the Shannon limit.

The ULF is even lower-frequency than MW. If a baud of 
20-symbols-per-second but 300 bits-per-symbol is used, can the luminance 
signal have its temporal and spatial frequencies downshifted 
sufficiently so that it can be on a ULF-frequency FM carrier? Will this 
work even if the FM carrier�s center-frequency is 300 Hz?

 > >Is there any thing that could be done to the QM signal so that the
 > >resulting FM sidebands won�t be excessive?
 >
 > >In an FM carrier, the neutral frequency results when there is no
 > >modulation signal. The FM carrier changes
 > >according to the modulator. If
 > >the modulator voltage it positive,
 > >the FM carrier�s frequency increases.
 > >When the modulator voltage becomes negative, the carrier�s frequency
 > >decreases. On a graph of the modulator signal,
 > >the x-axis is where the
 > >voltage is neutral. Above the x-axis,
 > >the voltage is positive. Below the
 > >x-axis, the voltage is negative.
 > >The further from the x-axis the voltage
 > >goes, the more broad the sidebands will be.
 >
 > >To prevent the sidebands from getting too broad,
 > >the QM signal needs to
 > >have all to voltages shifted closer to the x-axis.
 > >This means the device
 > >receiving the QM signals on the other end
 > >needs to be more sensitive to
 > >differences in voltages.
 >
 > >Thus it would help if the physical voltage difference between what is
 > >interpreted as 1 or 0 be much smaller. The smaller the change in
 > >voltage, the less extreme the resulting FM sidebands.

 > Your understanding of FM modulation is incomplete, and it is leading
 > you astray.  You're only looking at half of the picture.  You need to
 > go back and hit the books again so that you understand the whole
 > situation.
 >
 > Yes, it's true that the instantaneous carrier deviation depends only
 > on the amplitude of the modulation signal.  However, that's only part
 > of the picture.  Sidebands are created out *beyond* the maximum
 > carrier deviation frequency... and they are created at frequencies
 > which are at offset-multiples of the modulating frequency.
 >
 > You *cannot* narrow an FM signal down to a width less than the
 > modulating frequency.  If you want to carry (for example) an audio
 > signal with 20,000 Hz of audio bandwidth, then the modulated FM signal
 > will always have sidebands out as far as 20,000 Hz on either side of
 > the nominal carrier frequency.  This is true NO MATTER HOW SMALL the
 > amplitude of the modulating signal, as long as there's any signal at
 > all.
 >
 > If you FM-modulate a carrier with a very low-level 20 kHz tone, you
 > might be causing only 1 kHz of carrier deviation... but there will
 > still be sidebands 20 kHz above and below the nominal carrier
 > frequency.  That may seem strange and counterintuitive, but it's how
 > the math works out, and how measurements confirm it works.

So there is no way to decrease how far the sidebands will go?