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 ________________________________ 보낸 사람: Adrian Musceac <kanto...@gmail.com> 대신 Discuss-gnuradio <discuss-gnuradio-bounces+ksshin=postech.ac...@gnu.org> 보낸 날짜: 2018년 8월 25일 토요일 오후 5:13:09 받는 사람: discuss-gnuradio@gnu.org; Ron Economos 제목: Re: [Discuss-gnuradio] MAKING A NTSC TV RECEIVER 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 <w...@comcast.net> 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)" <muel...@kit.edu><mailto:muel...@kit.edu> 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 <i...@openend.se><mailto:i...@openend.se> 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 ________________________________
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