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Posted by Steven on 09/24/07 09:24
On Sep 24, 1:23 am, "Brian Gregory [UK]" <n...@bgdsv.co.uk> wrote:
> "Green Xenon [Radium]" <gluceg...@excite.com> wrote in messagenews:46f6f08e$0$16535$4c368faf@roadrunner.com...
>
> > Would using Quadrature Frequency Modulation be of any help?
>
> > 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?
>
> Think about it.
> Obviously there is no way FM and PSK can be going on at the same time in any
> way that can convey separate information. Worse still if you separately FM
> modulate two signals that start in quadrature with each other they won't
> stay in quadrature.
>
> --
>
> Brian Gregory. (In the UK)
> n...@bgdsv.co.uk
> To email me remove the letter vee.
Okay, I'll bite too. Why are you wanting to PSK? If you put them in
quadrature won't the phase differences try to cancel at points and
cause a mess?
Note: not my area of expertise but Brian raises some good points.
Wouldn't placing it in odd numbers on the carrier axis present fewer
problems...in other words IIRC the "constellation" mentioned earlier?
3 or 5 perhaps.
Would I be correct in thinking the Grand Alliance must have thought
around these lines originally before settling on an all-digital
system? It doesn't sound too feasable because it would take a lot to
duplicate all this signal and the transmissions would be awfully weak
IMO.
Anybody who has studied IBOC FM knows that the analog carrier noise
increases with IBOC added and each HD subchannel adds to this. The
laws of physics demand more power for those signals and it comes from
the analog signal in the end if you do not increase the total power,
which you cannot do given the nature of the allocations and power
restrictions given by the government. Only an ALL-DIGITAL system in
the end is not a compromise and burden to the existing channels.
Feel free to correct me where I'm goofy and thanks to the OP for
bringing up what I DON'T find boring or spam. I hope we're helping him
and you're doing the same.
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