Re: [Discuss-gnuradio] No horizontal sync with ntsc tv reception

[Eric Blossom]

On Mon, Oct 01, 2007 at 01:55:30PM -0500, Nirali Patel wrote:
> Hi,
> 
> 
> I am working on ntsc tv reception as a precursor to hdtv reception. I am
> using usrp_rx_cfile.py to capture samples to a file from the TV_RX board and
> then playing back using usrp_tv_rcv_nogui.py. The picture displayed does not
> seem to have horizontal sync (picture keeps moving from left to right). I
> have tried setting different decimation factors, the best I can use without
> overruns is a factor of 8 and the picture still rolls in horizontal
> direction. My understanding was that the decimation factor would only affect
> the horizontal resolution not the ability to sync, but I could be wrong. The
> commands that I use for capture and playback are:
> 
> ./usrp_rx_cfile.py -R B -d 16 -f 531.25M -s tv1.out 
> 
> ./usrp_tv_rcv_nogui.py -f 531.23M -n -i tv1.out sdl
> 
>  
> 
> where 531.25 Mhz is the picture carrier of the ntsc channel with lower band
> edge at 530Mhz.
> 
> I have also tried using -f 533M to set the tuning frequency to centre of the
> band but no significant change in picture sync.
> 
> If anyone has experienced similar problem I would appreciate the guidance.
> Does the antenna setting have any influence on h-sync? My office is in the
> interior of the building so would it help to move towards the exterior?
> 
> Thanks in advance for any help.
>
> Nirali Patel
> 

If you look at the code, there's a comment at the top that says that
synchroniziation isn't implemented:


  """
  Reads from a file and generates PAL TV pictures in black and white
  which can be displayed using ImageMagick or realtime using gr-video-sdl
  (To capture the input file Use usrp_rx_file.py, or use usrp_rx_cfile.py 
--output-shorts if you have a recent enough usrp_rx_cfile.py)
  Can also use usrp directly as capture source, but then you need a higher 
decimation factor (64)
  and thus get a lower horizontal resulution.
  There is no synchronisation yet. The sync blocks are in development but not 
yet in cvs.

  """


Eric