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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