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Re: [Discuss-gnuradio] signals/atsc question
From: |
Ilia Mirkin |
Subject: |
Re: [Discuss-gnuradio] signals/atsc question |
Date: |
Wed, 02 Mar 2005 01:41:49 -0500 |
> There are about 10.76 Msymbols/sec in an ATSC signal, so you are going
> to have Nyquist problems if you try to represent them in 8M complex
> samples/sec. You'll need at least 10.76 complex MS/s. (Indeed you
> may notice that we were skating inside the edge by using 20
> non-complex MS/s on the old hardware.) If we had a faster USB bus,
> the USRP could sample at a nice high rate, like 32 Msamples/sec, then
So... this probably stems from my shoddy understanding of signals and/or
information theory, but here is the question:
I have 8M complex S/s. This means that I *should* be able to do some
sort of quadrature demodulation or something along those lines to get a
full 8MHz of spectrum, no? Is this logic wrong? The FFT displays the
signal from -4 to +4 MHz... I was under the impression that the ATSC
signal was only 6MHz wide (if not a little less), so why do you need
21.52MS/s (real) to sample a 6MHz signal? Is this due to the
quantization of the measurements, and I would normally be right with
infinitely precise samples, but in the world of reality we live in, we
just have to oversample?
> The pcHDTV card uses a chip that's specialized and engineered to do
> this job very well in a variety of environments. By contrast, you are
> only about the fourth person to ever run the ATSC input code. It's a
> "dancing bear", which took more than a year of solid engineering just
> to get it dancing at all. It hasn't been optimized, either for CPU
> usage or for non-perfect signal reception.
Point well taken. There's a lot of multipath going on where I'm
receiving this.... might have to try for something different. I do have
a different antenna source; I'll try playing with it.
> I'll attach my favorite point script below. I thought it was in the
> source trees, but now I can't find it except on my hard drive.
>
Yeah, the wiki referred to it, but it wasn't in the gnuradio-0.9
tarball.
Thanks for the suggestions... I'll give them a whirl and see if I can
get anywhere.
---
Ilia Mirkin
address@hidden
- Re: [Discuss-gnuradio] signals/atsc question, John Gilmore, 2005/03/01
- Re: [Discuss-gnuradio] signals/atsc question, John Gilmore, 2005/03/02
- Re: [Discuss-gnuradio] signals/atsc question,
Ilia Mirkin <=
- Re: [Discuss-gnuradio] signals/atsc question, Eric Blossom, 2005/03/02
- Re: [Discuss-gnuradio] signals/atsc question, David Willmore, 2005/03/14
- RE: [Discuss-gnuradio] signals/atsc question, Robert McGwier, 2005/03/15
- Re: [Discuss-gnuradio] signals/atsc question, Eric Blossom, 2005/03/16
- RE: [Discuss-gnuradio] signals/atsc question, Chuck Swiger, 2005/03/16
- RE: [Discuss-gnuradio] signals/atsc question, Matt Ettus, 2005/03/17
- RE: [Discuss-gnuradio] signals/atsc question, Robert McGwier, 2005/03/17
Re: [Discuss-gnuradio] signals/atsc question, Marcus Leech, 2005/03/02