On 8/17/07, Jan Schiefer <[EMAIL PROTECTED]> wrote: > Vijay Ramasami wrote: > > 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 <[EMAIL PROTECTED]> 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, [EMAIL PROTECTED] 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." > >> > >> > >> > If you can't find any, let me know and I might be able to help. I have > access to 2 QAM-64 channels and 15 or so QAM256 channels, some HD, all > unencrypted. I probably have some encrypted ones too, but I don't know > how many, as they are encrypted... If you can write a little capture > program, I can try to hook up the USRP to the cable jack and see whether > I can capture something. Problem is, I don't have a TVRX (yet), but this > that may be a good excuse to order one. :-). Provided the phase response > of the TVRX is sufficiently flat for this kind of signal. Anybody have a > guess? > > Cheers, > Jan >
Hi Jan, I would highly appreciate it if you can capture a few QAM-64 snapshots. I was able to successfully demodulate signals captured from a QAM modulator, but I don't have access to a real-world cable source. I guess the python script "usrp_rx_cfile.py" (in the examples directory) can be used to capture samples. We need at least 16 MHz sampling frequency for symbol timing recovery to work properly. Thanks, Vijay. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
