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Is QFM ever used? Can it decrease the bandwidth needs of FM video signals?

Started by Green Xenon [Radium] September 23, 2007
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
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
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?
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 >
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.
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
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. &macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;
Regard video signals -- couldn&#2013266066;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&#2013266066;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 :

&#2013266067;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.&#2013266068;

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 
:

&#2013266067;So the technique is to try and "pack" as many bits as you can into 1 baud.&#2013266068;

So it&#2013266066;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
Green Xenon [Radium] wrote:
> Regard video signals -- couldn&#2013266066;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&#2013266066;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
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