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Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER
From: |
CEL |
Subject: |
Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER |
Date: |
Fri, 24 Aug 2018 19:42:17 +0000 |
Hi Martin,
internally, the RTL dongles are fast enough to capture full DVB-T (not
-T2) channels, and demodulate, and decode them, and deliver the video
stream to the host. However, RTL-SDR can't use that mode - it uses a
"bypass the whole Digital TV specific stuff" mode and directly passes
IQ samples through USB.
In that mode, it simply can't do more than 2 or 3 MS/s (can't
remember), which isn't enough to cover 6 MHz - so everyone's right, you
can basically receive the AM black/white info at a partial bandwidth of
the ca 5 MHz of the luma signal, but you won't get any color
information that way, or audio with the same receiver as you do video.
Cheers,
Marcus
On Fri, 2018-08-24 at 12:22 -0500, Martin McCormick wrote:
> 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
>
> _______________________________________________
> Discuss-gnuradio mailing list
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- [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Andres Campos Santana, 2018/08/23
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, CEL, 2018/08/24
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Ralph A. Schmid, dk5ras, 2018/08/24
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Ron Economos, 2018/08/24
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Anders Hammarquist, 2018/08/24
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Martin McCormick, 2018/08/24
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER,
CEL <=
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Adrian Musceac, 2018/08/25
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Ron Economos, 2018/08/25
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Adrian Musceac, 2018/08/25
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Ron Economos, 2018/08/25
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Kyeong Su Shin, 2018/08/25
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Adrian Musceac, 2018/08/25
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Martin McCormick, 2018/08/25
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Andres Campos Santana, 2018/08/25
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Martin McCormick, 2018/08/27
- Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER, Andres Campos Santana, 2018/08/27