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Re: [Discuss-gnuradio] Questions on US digital cable ...

From: Vijay Ramasami
Subject: Re: [Discuss-gnuradio] Questions on US digital cable ...
Date: Tue, 14 Aug 2007 10:55:40 -0400

Thanks for the information David. I will look up ITU-J.83B ...

Do you happen to have any captured QAM cable data (or any website that
lists the data) ? I wanted to see if I can put together a software
demod for digital cable ...

On 8/13/07, David I. Emery <address@hidden> wrote:
> On Mon, Aug 13, 2007 at 10:52:54AM -0400, Vijay Ramasami wrote:
> > Hi,
> >
> > I have a couple of questions:
> >
> > 1. Does the US digital cable system follow the DVB-C standard (or one
> > of its annexes) ? Is there any information (website) on the typical
> > symbol rates, bandwidths (I am guessing approx 6 MHz), used ?
>         There is a Cablelabs spec that defines what is used.   The ETSI
> standards (ITU-T J.83B) also define the particular parameters as well.
>         I can look up detailed references if needed...
>         The are actually only two standard modulations in wide use 64QAM
> with a particular set of parameters that yields a 30 Mb/s signal with a
> 5.056941 Msym/symbol rate and a 256QAM signal which yields a 38.9 Mb/s
> signal with a symbol rate of 5.360537 Msym/s
>         Both signals are 6 MHz wide as US CATV is universally 6 MHz
> channel based.
> > 2. Has anyone successfully captured (preferably unencrypted) digital
> > QAM transmissions using the USRP ? If so, can you please send me a
> > link to the data ? Given that the symbol rates are in the range of 5-6
> > Ms/s, it must be possible to use 16 MHz sampling frequency to
> > demodulate the signals.
> >
>         I have used a number of purpose built demods, but not yet tried
> a USRP solution.   Some of the cable transport streams have open
> channels, but you will find most are encrypted except the local OTA HD
> signals and a few freebie promos.
>         It is also possible to MODULATE QAM cable standard signals,
> something that gets more useful every month as more QAM/ATSC tuners are
> shipped for cable ready setups with CableCards rather than set top
> boxes.   This of course allows direct input of MPEG transport streams
> into the digital domain of LCD/plasma panels with no analog step...
> --
>   Dave Emery N1PRE/AE, address@hidden  DIE Consulting, Weston, Mass 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
> celebration of what could have been, but wasn't and is not to be now either."

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