Jan, Sorry. I have been out of touch with GNURadio for a while. I am very happy to hear that you have some data available to test. I would really appreciate it if you can find time to upload your data (whatever size you are comfortable with - I have a fast connection and hence 270MB should download fairly quickly). I am ready to jump back in.
Thanks again, Vijay. On Fri, Sep 21, 2007 at 1:28 AM, Jan Schiefer <[EMAIL PROTECTED]> wrote: > > Vijay Ramasami wrote: > > > 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. > > > > > Hi Vijay, > > sorry this is taking so long, but I think I have what you need now. With a > 16MHz sampling frequency you get only 8 bits of resolution, so I was a > little skeptical as to whether this would be sufficient. I played around > with a 10 second QAM64 snapshot (640MB, stored as 16-bit signed ints, which > gzips down to around 270MB). I put a chunk of this data into the Agilent > 89600 Vector Signal Analyzer software, and with equalization turned on, the > constellation actually looks pretty reasonable. So what I captured must not > be complete garbage :-). > > Let me know if you still need this and I find a shady spot on the web to > put it. Or if you'd rather have something shorter, or stored as floats, let > me know. > > Cheers, > Jan > > _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
