No horizontal sync with ntsc tv reception

GNU Radio
1

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 P.

2

On Mon, Oct 01, 2007 at 01:55:30PM -0500, Nirali P. wrote:

the horizontal resolution not the ability to sync, but I could be wrong. The

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