Thread View: uk.tech.digital-tv
7 messages
7 total messages
Started by Green Xenon [Radium]
Tue, 25 Sep 2007 02:27
Re: Using an FM-Carrier for the Y [Luminance] Signal -- how to relieve the bandwidth issue?
Author: Green Xenon [Radium]
Date: Tue, 25 Sep 2007 02:27
Date: Tue, 25 Sep 2007 02:27
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On Sep 23, 2:36 pm, "Brian Gregory [UK]" <n...@bgdsv.co.uk> wrote in http://groups.google.com/group/uk.tech.digital-tv/msg/6a386fec832f1ef5 : > "Green Xenon [Radium]" <gluceg...@excite.com> wrote in messagenews:46f6d850$0$11068$4c368faf@roadrunner.com... > > > Hi: > > One major reason the luminance signals of > > television are broadcasted on an > > AM-carrier instead of FM is > > because FM requires large amounts of > > bandwidth. Is there a way to use FM video > > without hogging so much > > bandwidth? > > 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 Quadrature Modulation > > 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? > No. > > These are like special modified forms of AM. > > You can only use these to reduce > bandwidth of an FM signal in the same way > that you can use AM to reduce > the bandwidth of an FM signal. > It just won't > be FM any more. 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
Re: Using an FM-Carrier for the Y [Luminance] Signal -- how to relieve the bandwidth issue?
Author: Dave Platt
Date: Tue, 25 Sep 2007 05:41
Date: Tue, 25 Sep 2007 05:41
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In article <46f86fa7$0$9596$4c368faf@roadrunner.com>,
Green Xenon [Radium] <glucegen1@excite.com> wrote:
>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.
Hope all you want, guy.
Don't hold your breath while you're hoping for it, though.
To understand why, Google the "Shannon Limit".
--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Re: Using an FM-Carrier for the Y [Luminance] Signal -- how to relieve the bandwidth issue?
Author: Steven
Date: Tue, 25 Sep 2007 06:28
Date: Tue, 25 Sep 2007 06:28
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On Sep 24, 11:41 pm, dpl...@radagast.org (Dave Platt) wrote: > In article <46f86fa7$0$9596$4c368...@roadrunner.com>, > Green Xenon [Radium] <gluceg...@excite.com> wrote: > > >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. > > Hope all you want, guy. > > Don't hold your breath while you're hoping for it, though. > > To understand why, Google the "Shannon Limit". That Shannon sure is limited!
Re: Using an FM-Carrier for the Y [Luminance] Signal -- how to relieve the bandwidth issue?
Author: Rick Merrill
Date: Tue, 25 Sep 2007 17:59
Date: Tue, 25 Sep 2007 17:59
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Steven wrote: > On Sep 24, 11:41 pm, dpl...@radagast.org (Dave Platt) wrote: >> In article <46f86fa7$0$9596$4c368...@roadrunner.com>, >> Green Xenon [Radium] <gluceg...@excite.com> wrote: >> >>> 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. >> Hope all you want, guy. >> >> Don't hold your breath while you're hoping for it, though. >> >> To understand why, Google the "Shannon Limit". > > That Shannon sure is limited! > "...signal power through an analog communication channel subject to additive white Gaussian noise..." In other words it is obsolete because FM video is going away on Feb 18, 2009.
Re: Using an FM-Carrier for the Y [Luminance] Signal -- how to relieve the bandwidth issue?
Author: Brian Gregory [UK]
Date: Tue, 25 Sep 2007 20:36
Date: Tue, 25 Sep 2007 20:36
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"Green Xenon [Radium]" <glucegen1@excite.com> wrote in message news:46f86fa7$0$9596$4c368faf@roadrunner.com... > 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. Why????? Why make it use more bandwidth by introducing totally superfluous FM modulation?? I'm beginning to think you are a troll. -- Brian Gregory. (In the UK) ng@bgdsv.co.uk To email me remove the letter vee.
Re: Using an FM-Carrier for the Y [Luminance] Signal -- how to relieve the bandwidth issue?
Author: Richard Crowley
Date: Tue, 25 Sep 2007 20:46
Date: Tue, 25 Sep 2007 20:46
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"Brian Gregory [UK]" wrote ... > Why make it use more bandwidth by introducing totally superfluous FM > modulation?? > > I'm beginning to think you are a troll. Others have come to the same conclusion months ago.
Re: Using an FM-Carrier for the Y [Luminance] Signal -- how to relieve the bandwidth issue?
Author: Sjouke Burry
Date: Tue, 25 Sep 2007 20:47
Date: Tue, 25 Sep 2007 20:47
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Brian Gregory [UK] wrote: > "Green Xenon [Radium]" <glucegen1@excite.com> wrote in message > news:46f86fa7$0$9596$4c368faf@roadrunner.com... >> 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. > > Why????? > > Why make it use more bandwidth by introducing totally superfluous FM > modulation?? > > I'm beginning to think you are a troll. > Stop wondering, he IS a troll, asking wrong,silly questions, and crossposting all over the place, hoping to score from people who think the questions are legit.
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