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

Hello Adrian,

The USB interface is integrated in the RTL-SDR chip (RTL2832U), so it cannot be replaced (as far as I know).

In theory, USB 2.0 can support faster data rates (HackRF does 16 MS/s - 20 MS/s with USB 2.0 8 bit I-Q). As Ron mentioned, it is due to the cost reduction.

Regards,

Kyeong Su Shin

Hi Ron,

So in theory, replacing the USB2 chip with a USB3 would allow access to the full sample rate, or is there some other internal limitation?

Regards,
Adrian

On August 25, 2018 8:06:20 AM UTC, Ron Economos <address@hidden> wrote:

The maximum Transport Stream rate of DVB-T is 31.67 Mbps, so the USB interface only needs to deliver 4 MB/s. Since you need two 8-bit samples in IQ mode, it's 2 Msps.

Ron

On 08/25/2018 12:44 AM, Adrian Musceac wrote:

Hi Marcus,

You're right about the RTL sample rate, but I'm curious about why it is so small.
Is it the bus speed? The ADC is obviously fast enough for DVB-T2.

Regards,
Adrian

On August 24, 2018 7:42:17 PM UTC, "Müller, Marcus (CEL)" <address@hidden> wrote:

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

From:	Kyeong Su Shin
Subject:	Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER
Date:	Sat, 25 Aug 2018 08:31:57 +0000