FYI, I've fiddled with NTSC a bit. One big help is to work on Cable instead of OTA. Cable has a hundred channels that the tvrx can tune to with high snr and little multipath. I also determined that a 2 MSPS data rate seems to be enough for a basic black and white image, although its best to interpolate back up by 4x to get good horizontal resolution in the image.
----- Original Message ----- From: Martin Dvh <[EMAIL PROTECTED]> Date: Tuesday, August 9, 2005 9:38 am Subject: [Discuss-gnuradio] tv-reception > Hi all, > Prateek Dayal wrote: > > have u had any success with tv reception on gnuradio .... I am all > > caught up in a new job here and still fighting out to take out some > > time to work on this .. even my net connection has not been > installed> yet at home :( > John Gilmore wrote: > > Thanks for your ongoing work on this. Television, here we > come! The > > next part, I think, will be looking for the sync pulse, > throwing away > > the samples before it. Eric has written such code before for > HDTV, he > > can suggest where to look or what to do. (He's improved the core > > buffer/sched code since then too, and may recommend using a new > > capability.) > Eric, can you give a hint? > > > > Copyright notice on the new code should be 2005, e.g. in > gr_float_to_uchar. > (There's always *some* nit that could be > improved!)I will patch this nasty bug ;-) > > > I am working on it right now. > There is a preliminary tv-reception example in cvs now. > gnuradio-examples\python\usrp\tvrx_tv_rcv.py > I got some images that way. > > I am working on improved code right now. > (Got some better images) > First thing was to convert to unsigned char in stead of char. > > Next thing is an agc (I have a somewhat working version of an agc, > using standard blocks in python which is quite computationally > intensive)I also made an gr_agc_ff block based on gr_agc.h which > should work better/faster. > > Using an agc you can get rid of the scale and offset parameter in > the tvrx_tv_rcv.py example. > > What I am doing now is building a block which does am detection > using a synchronous am_detector in stead of complex_to_mag > (this block contains agc, pll and complex multiplier. This is all > in one block because the different signals for phase-detection and > agc are > re-used and interact with each-other) > This is mainly based on the FPLL which is in the old atsc code. > > This block is also quite computationally intensive but should give > us a cleaner video signal. > I haven't decoded video with it yet, but is seams to lock to a > generated sinus if the initial frequency is close enough. > > I want to have a clean and stable videosignal before we try to > detect the sync-pulses. > > I found that the right setting for rfgain and ifgain in the tvrx > frontend is quite important. > This should be included in the agc loop but I don't know yet how. > Is there a way to send and get signals to other blocks in the flow- > graph?(This will probably be usrp tvrx specific so this code > probably can't go into gnuradio-core) > > Greetings, > Martin > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
