Posted by Brian Gregory [UK] on 09/23/07 21:36

"Green Xenon [Radium]" <glucegen1@excite.com> wrote in message
news: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.

--

Brian Gregory. (In the UK)
ng@bgdsv.co.uk
To email me remove the letter vee.

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