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Re: [Discuss-gnuradio] decoding NTSC tv

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] decoding NTSC tv
Date: Fri, 10 Jun 2011 18:52:02 -0400

On Fri, Jun 10, 2011 at 3:12 PM, open bts <address@hidden> wrote:
I'm looking to decode NTSC with my gnuradio.  I found this
http://www.danielgarcia.info/thesis/ online where someone used
an older USRP and gnuradio version to decode NTSC and PAL.
I was able to mangle his script a bit to run with newer gnuradio
and UHD.  (I hard-coded in some of the parameters for quick 
testing, it needs some polish once completed).
However I still just get a black screen, so we're not
all the way there yet.

Anyone around familiar with this code?  The original code seemed
to have a sample rate of around 1Ms/sec (ie. adc rate 64M decimated
64 times, if I read the code correctly).  Is this enough for a tv signal?
It looks like an NTSC channel is around 6M wide (with color and
sound), right?

I've not played with this code, no, but 1 MHz bandwidth doesn't sound like it'll work. You can see the spectrum mask here: http://en.wikipedia.org/wiki/NTSC

1 MHz doesn't get you a whole lot of information in NTSC. You really need the entire 6 MHz.
I'm going to try to get a stronger signal to test with and play with
it some more, but if anyone is interested in helping, I'd welcome
the assistance.

Where are you getting NTSC transmissions now, anyway? Only low power TV is left in the US to transmit on NTSC, and I think most of them have moved away from it, too. I'm sure there's still signals out there, I'm just wondering where and what services would still be using it. I also don't know the state of NTSC outside of the US, but it was fairly limited to being with.


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