On Sep 24, 10:32 pm, "Green Xenon [Radium]" <gluceg...@excite.com>
wrote:
> Regard video signals -- couldn't the video signal first be converted to
> QAM, multiple-level quadrature modulation, and/or constellation
> modulation and then transmitted on a FM radio carrier?
>
> AFAIK, the QAM/multiple-level-QM/ constellation-modulation version of
> the video signal won't require as much bandwidth as the original video
> signal. The original video signal is first converted to bits and symbols
> and then transmitted on an FM radio carrier. To make the best use of
> bandwidth, limit the baud to only 1-symbol-per-second but pack as many
> bits-per-symbol as feasible.
There's a problem with packing in a lot of bits per symbol. Multilevel
modulation requires increasingly large SNR to achieve reliable
communication. Even in really high SNR environments (40-50 dB), you
might only be able to pack 8 or 10 bits per symbol, which would limit
the system you suggested to 8 or 10 bits per second. This sort of
assumes that you would use an FM discriminator to translate the
varying frequency into a baseband stream of multi-level pulses, but
you run into issues with other FSK detection methods also. You're just
not going to be able to stuff hundreds or thousands of bits into a
single symbol.
Jason
Reply by glen herrmannsfeldt●September 25, 20072007-09-25
Green Xenon [Radium] wrote:
> Regard video signals -- couldn�t the video signal first be converted to
> QAM, multiple-level quadrature modulation, and/or constellation
> modulation and then transmitted on a FM radio carrier?
That sounds somewhat like FM stereo.
> AFAIK, the QAM/multiple-level-QM/ constellation-modulation version of
> the video signal won�t require as much bandwidth as the original video
> signal. The original video signal is first converted to bits and symbols
> and then transmitted on an FM radio carrier. To make the best use of
> bandwidth, limit the baud to only 1-symbol-per-second but pack as many
> bits-per-symbol as feasible.
QAM is a tradeoff between S/N and bandwidth.
FM is a tradeoff between bandwidth and S/N.
If you are lucky they will balance out.
-- glen
Reply by Green Xenon [Radium]●September 24, 20072007-09-24
Regard video signals -- couldn�t the video signal first be converted to
QAM, multiple-level quadrature modulation, and/or constellation
modulation and then transmitted on a FM radio carrier?
AFAIK, the QAM/multiple-level-QM/ constellation-modulation version of
the video signal won�t require as much bandwidth as the original video
signal. The original video signal is first converted to bits and symbols
and then transmitted on an FM radio carrier. To make the best use of
bandwidth, limit the baud to only 1-symbol-per-second but pack as many
bits-per-symbol as feasible.
Quotes from http://en.wikipedia.org/wiki/Baud :
�Conveying more than one bit per symbol has advantages. It reduces the
time required to send a given quantity of data, and allows modern
modems, FDDI and 100/1000 Mbit/s Ethernet LANs, and others, to achieve
high data rates. An optimal symbol set design takes into account channel
bandwidth, desired information rate, noise characteristics of the
channel and the receiver, and receiver and decoder complexity. A typical
2400-bit/s modem transmits at 600 baud (600 symbol/s), where each
quadrature amplitude modulation symbol carries four bits of information.
1000 Mbit/s Ethernet LAN cables use many wire pairs and many bits per
symbol to encode their data payloads. 1000BASE-T uses four wire pairs
and two data bits per symbol to get a symbol rate of 125MBd.�
Quotes from
http://www.howstuffworks.com/framed.htm?parent=modem.htm&url=http://www.physics.udel.edu/wwwusers/watson/student_projects/scen167/thosguys/index.html
:
�So the technique is to try and "pack" as many bits as you can into 1 baud.�
So it�s always best to use the most amounts of bits-per-baud but no more
than 1 baud
bps = baud * number of bits per baud.
Remember, keep the baud no more than one-symbol-per-second but at the
same time, convey as many bits-per-symbol as mathematically and
physically possible.
Then, hopefully, it will be possible to transmit/receive video signals
on FM carriers with radio-frequencies below the medium-wave band --
without stealing bandwidth from existing stations using those
frequencies -- or frequencies near those stations.
http://en.wikipedia.org/wiki/Medium-wave
MW = from 530 kHz up to 1610 kHz
Reply by Jerry Avins●September 24, 20072007-09-24
Green Xenon [Radium] wrote:
...
> By "orthogonal polarization" are you referring to Orthogonal
> frequency-division multiplexing?
No, he isn't. Are you familiar with those color 3-D movies that require
the viewer to wear special glasses? Those glasses have Polaroid filters
orthogonally oriented and two images, also orthogonally oriented, are
projected onto the viewing screen. One image is seen by the left eye,
the other by the right. Radio waves are polarized by the antenna, and
the same scheme can be used at the receiver to separate them.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●September 24, 20072007-09-24
On Sep 24, 2:06 pm, "Green Xenon [Radium]" <gluceg...@excite.com>
wrote:
> Related questions below:
>
> What is the FM-equivalent of QAM?
>
> What is the FM-equivalent of "constellation modulation"?
>
> What is the FM-equivalent of multiple-level quadrature modulation?
You should do some reading in a digital communications textbook to
understand more clearly what a signal constellation is. There's
nothing special tying constellations to QAM, or any other specific
modulation scheme. A constellation is just a plot of symbol locations
in (often two-dimensional) space. The symbol space is often assumed to
be the complex plane, which allows for a compact complex-number
representation to be used for the locations in the constellation. Each
modulation scheme translates the digital symbols (or, potentially,
complex numbers) to waveforms in their own way. A constellation
doesn't define the output waveform independently; it only defines the
symbol locations that correspond to the system's discrete alphabet.
The modulation scheme then defines how the symbols are mapped into
waveforms for transmit.
In "quadrature" modulation schemes, the coordinates of each symbol
location are used as coefficients on quadrature carriers (i.e. two
carriers 90 degrees apart). The resulting carriers are summed
together, which yield a single carrier of some symbol-dependent
amplitude and phase. This interpretation is why you refer to QAM being
a mixture of AM and PSK, as the resultant carrier that gets
transmitted is modulated both in amplitude and phase. If you
restructure the constellation such that the symbols have a constant
distance from the origin, then you're left with a modulated carrier
that has constant envelope but varying phase, or just plain PSK.
I guess the FM-equivalent of multiple-level modulation would be higher-
order FSK, like 4-FSK. However, as glen pointed out, I don't believe
it's practical to do QFM, as the resulting carriers would not be in
quadrature. The quadrature receiver is a relatively fundamental
building block in communications systems; you might research that
topic as well.
Jason
Reply by Green Xenon [Radium]●September 24, 20072007-09-24
Sorry for the repeated message below. I posted it on accident. I quoted
Glen but didn't add any of my own words. Sorry for the annoyance it
causes. I just f--king hate it when crap that happens!!!!!!!!!!!!!!!!!
If only I could crack into all the world's Usenet servers and remove
that message.
http://groups.google.com/group/comp.dsp/msg/874fe22b1c51cc38
Once again, I apologize profusely for this accident.
Reply by Green Xenon [Radium]●September 24, 20072007-09-24
glen herrmannsfeldt wrote:
> Green Xenon [Radium] wrote:
>
>> Is Quadrature Frequency Modulation used? What for?
>
>
> As far as I know, there is no such thing.
>
>> AFAIK, Quadrature Amplitude Modulation uses a combo of AM and
>> Phase-Shift-Keying.
>
>
> The usual description is amplitude modulating two carriers 90 degrees
> apart. That is how NTSC describes it. With synchronous demodulation
> two signals can be separated out. For FM two separately modulated
> carriers would not stay in quadrature.
>
> Well, there is one thing that does work. Satellite TV works
> with 25MHz FM channels spaced 12.5MHz apart at orthogonal polarization.
> Not really QFM but it does get more signals in the same bandwidth.
>
>> So QFM would use a combination of FM and PSK. Would this decrease the
>> bandwidth required for broadcasting FM luminance video signals?
>
>
>> I did a Google Search for �Quadrature Frequency Modulation� on
>> http://www.google.com/search?hl=en&lr=&q=%22Quadrature+Frequency+Modulation+%22&btnG=Search
>
>
>
> It looks like all the references are to one patent. I still don't
> believe it, but it seems that the USPTO does.
>
> -- glen
>
Reply by Green Xenon [Radium]●September 24, 20072007-09-24
glen herrmannsfeldt wrote:
> Green Xenon [Radium] wrote:
>> Is Quadrature Frequency Modulation used? What for?
> As far as I know, there is no such thing.
Is it technically-possible for QFM to exist, though?
>> AFAIK, Quadrature Amplitude Modulation uses a combo of AM and
>> Phase-Shift-Keying.
> The usual description is amplitude modulating two carriers 90 degrees
> apart. That is how NTSC describes it. With synchronous demodulation
> two signals can be separated out. For FM two separately modulated
> carriers would not stay in quadrature.
Okay.
> Well, there is one thing that does work. Satellite TV works
> with 25MHz FM channels spaced 12.5MHz apart at orthogonal polarization.
> Not really QFM but it does get more signals in the same bandwidth.
By "orthogonal polarization" are you referring to Orthogonal
frequency-division multiplexing? If so, is this the FM-equivalent of
QAM? If not, then what is the FM-equivalent of QAM?
http://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing
Related questions below:
What is the FM-equivalent of QAM?
What is the FM-equivalent of "constellation modulation"?
What is the FM-equivalent of multiple-level quadrature modulation?
Reply by glen herrmannsfeldt●September 24, 20072007-09-24
Green Xenon [Radium] wrote:
> Is Quadrature Frequency Modulation used? What for?
As far as I know, there is no such thing.
> AFAIK, Quadrature Amplitude Modulation uses a combo of AM and
> Phase-Shift-Keying.
The usual description is amplitude modulating two carriers 90 degrees
apart. That is how NTSC describes it. With synchronous demodulation
two signals can be separated out. For FM two separately modulated
carriers would not stay in quadrature.
Well, there is one thing that does work. Satellite TV works
with 25MHz FM channels spaced 12.5MHz apart at orthogonal polarization.
Not really QFM but it does get more signals in the same bandwidth.
> So QFM would use a combination of FM and PSK. Would this decrease the
> bandwidth required for broadcasting FM luminance video signals?
It looks like all the references are to one patent. I still don't
believe it, but it seems that the USPTO does.
-- glen
Reply by Green Xenon [Radium]●September 23, 20072007-09-23
Hi:
Is Quadrature Frequency Modulation used? What for?
AFAIK, Quadrature Amplitude Modulation uses a combo of AM and
Phase-Shift-Keying.
So QFM would use a combination of FM and PSK. Would this decrease the
bandwidth required for broadcasting FM luminance video signals?
I did a Google Search for �Quadrature Frequency Modulation� on
http://www.google.com/search?hl=en&lr=&q=%22Quadrature+Frequency+Modulation+%22&btnG=Search
None of those pages made any sense to me.
One major reason the luminance signals of television are broadcasted on
an AM-carrier instead of an FM-carrier is because FM requires large
amounts of bandwidth. Is there a way to use FM video without hogging so
much bandwidth using QFM?
Quotes from
http://groups.google.com/group/sci.electronics.basics/msg/0c013cf5371da8dc?hl=en&
:
>Multiple-level quadrature modulation,
>"constellation modulation",
>is most common for packing
>lots of bits per Hz of bandwidth.
>The more you pack,
>the better the s/n ratio has to be.
>http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation
>http://en.wikipedia.org/wiki/Constellation_diagram
Does this mean that the FM-equivalents-of-QAM and Constellation
Modulation can -- at least in theory -- be applied to FM video so that
excessive bandwidth is not needed? If so, then what would be the minimum
radio-frequency required to transmit the video signal?
Constellation modulation is a type of AM. What�s the FM-equivalent of
constellation modulation?
Has multiple-level QFM ever been used for video before?
Any assistance is greatly appreciated.
Thanks a bunch,
Radium