Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER

[Martin McCormick]

        First, I will talk about the things I know for sure.  The
NTSC analog system as well as Pal systems in a lot of the rest of
the world had a lot in common with eachother.  Both systems
transmitted an AM video signal in Vestigial single sideband mode
such that the carrier frequency was always about 1.25 MHZ above
the start of a channel.  NTSC systems in the Americas also
transmitted an audio carrier in FM which was always 4.9 MHZ above
the video carrier.  Pal systems used exactly the same type of
transmissions except that the 625-line video at 25 frames per
second made a slightly wider spectrum such that the audio and
video carriers were separated by 5.x MHZ, making each Pal channel
7 or 8 MHZ wide.

        As others have suggested, you could probably get a
monochrome fuzzy image if you can get your sound card to sample
fast enough.  You can also decode the mono sound by setting your
RTL receiver to behave just like a FM broadcast receiver but set
the frequency to whatever the video carrier frequency is plus 4.5
MHZ.  if the video carrier is 55.250 MHZ, the audio will be at
59.75 MHZ.  The deviation is 75 KHZ unlike FM radio which is 150
KHZ.

        That would be a good simple test to see if you are
receiving the channel at all.

        I am guessing that since the RTL chips were designed for
the European television market for cable and over-the-air
broadcasts, they can be sampled extremely fast since the digital
channels still take up the same bandwidth as their analog
ancestors.

        Martin McCormick WB5AGZ

Anders Hammarquist <address@hidden> writes:
> In a message of Fri, 24 Aug 2018 10:27:40 +0200, "Ralph A. Schmid, 
> dk5ras" writes:
> >> Hi Andres,
> >>
> >> just had a short look: doesn't NTSC use a nearly 6 MHz bandwidth?
> >>
> >> Best regards,
> >> Marcus
> >
> >Yes, no way with the RTL to catch NTSC, it does in SDR mode only 2.smth 
> MHz bandwidth.
> 
> Actually, you should be able to get a picture. The horizontal resolution 
> will be
> about half of what it would be for the full bandwidth, and no colour (as 
> the colour
> subcarrier at 3.58 MHz is outside the pass band). You want the pass band 
> of the reciever
> from just below the video carrier and as high as it will go.
> 
> /Anders