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Re: [Discuss-gnuradio] tv-reception

From: cepope
Subject: Re: [Discuss-gnuradio] tv-reception
Date: Tue, 09 Aug 2005 17:33:21 -0400

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 <address@hidden>
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
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