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> 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> 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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