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Posted by Green Xenon [Radium] on 09/24/07 04:50
On Sep 23, 3:02 pm, Brendan Gillatt
<brendanREMOVET...@brendanREMOVETHISgillatt.co.uk> wrote in
http://groups.google.com/group/uk.tech.digital-tv/msg/4c903b0a453a39fa :
> Okay now you're actualy irritating me quite a LOT.
How so? I am just asking extremely interesting questions about video
technology.
> Please, do yourself a favour: buy an Amazon book voucher and shut up.
I’ve tried painfully hard to answer my questions doing my own research
-- including reading information from books. I still haven’t found
answers to my questions. That is why I am turning to NGs for assistance.
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? Is a 150 kHz
radio-frequency sufficient to be an FM carrier for this 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?
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