Eric A. Cottrell wrote: > Martin Dvh wrote: > >>Cory Papenfuss wrote: >> >>>>I have a digital-wip branche which is work in progress for digital QAM >>>>stuff >>>>and >>>>general-wip which is my work in progress for general gnuradio things >>>>(latest addition is gr-cxadc, a driver for cx2388x capture cards to >>>>use as a general purpose high-speed ADC frontend as a cheap >>>>alternative for >>>>an USRP) >>>> >>>>Greetings, >>>>Martin >>>> >>> >>> Has there been some progress on that front then? I've been lurking >>>here for awhile, but last time I looked into this I don't think the TV >>>-capture cards were viable. The BT8xx chips still have holes in the >>>data, right? CX2388x can stream baseband without VBI holes? >> >>Yes they can. >> >>Look in the mailinglist for TV card SDR: >>http://lists.gnu.org/archive/html/discuss-gnuradio/2007-04/msg00134.html >>http://lists.gnu.org/archive/html/discuss-gnuradio/2007-04/msg00042.html >> >>How Chee page on this: >>http://www.geocities.com/how_chee/cx23881fc6.htm >>My page on this: >>http://www.olifantasia.com/projects/gnuradio/mdvh/cx2388x/cxadc/ >> >>SVN files are in >>http://gnuradio.org/trac/browser/gnuradio/branches/developers/nldudok1/general-wip >>cxadc is the kernel driver >>gr-cxadc is the gnuradio driver/glue >>gnuradio-examples/cxadc are the example scripts >> > > Hello, > > What are the sampling rates for these cards? Can they go up to 8 or 10 > MSPS? If so I might be able to try them out with Mode S. You could try them out.
Standard is 28.63636.0 MSPS which is normally converted using a built-in samplerateconverter to 27 MSPS. (The samplerateconversion is configurable but this is not implemented in the driver yet) So you can capture up to 14 Mhz wide signals. I "overclocked" mine to run at 32.0 MSPS to be able to use a tuner with a 44 Mhz IF freq. (with 28.63636 MSPS you have a niquist boundary at 42.95 Mhz which is right in the 40 - 48 Mhz bandpass of the 44 Mhz IF) You must also know that the ADC is 10 bits of which you standard only get the high 8 bits, so you don't have a very high dynamic range. (using some tricks it should be possible to get the full 10 bits at halve the samplingrate) I must say this is still work-in-progress quality. A lot of these tv-cards do not have a tuner with a suitable IF-output (if any) or only a "narrow-band" 200 kHz If at 10.7 MHz. The IF-output level usually also is much too low (1 to 100 mv) for the video-input (1 V) to use the complete dynamic range. Amplification needs top be added to get better sensitivity and dynamic range. To have the most fun, you also really want a tuner with a 8 Mhz wide IF at the right IF-freq. For now I get the best results when using an external microtune tuner with a 5.75 Mhz IF. I am working on getting the built-in thomson tuner of my pcHDTV3000 cx2388xx tv-card usable. So the main work ahead is finding out which tuners are suitable, how to connect them to the video-input (amplification) and how to tune them. The end-product will not be equivalent to an usrp but it will be a low-budget way to do SDR with gnuradio on quite a broad frequency range. (0-50 Mhz using direct sampling and 50-860 Mhz using tuner) If there is interest I am willing to supply premodified cards with the tuner replaced with a suitable model. (As soon as we have a good working setup) Greetings, Martin > > 73 Eric > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
