[Discuss-gnuradio] My First HDTV screenshot from USRP

[mao mao]

Hi,
Finally, I got my first HDTV screenshot tonight. It's
from KTVU's "The Loop".

Here's how I did it:
1) Download ATSC stream off USRP with the following
parameters:
TVRX's rf freq = 725e6
USRP's center freq = 43.75e6
Decim = 8
TVRX's Gain = 88;
USRP's format = 0x300
Mux = 0xf0f0f0f0

See ktvu-complex.png for the FFT pic

2) Upsample 8Ms/s complex data to 40Ms/s complex data:

for every sample in the 8Ms/s data, add 4 zeros, then
followed by a lowpass filter.

3) Downsample 40Ms complex data to 20Ms/s complex
data:
remove every other sample from the 40Ms/s sample data

4) Frequency Translate the center frequency from 0Hz
to 5.75MHz

5) Keep the In-phase part of the 20Ms/s complex data
to get 20Ms/s real data:

See ktvu-real.png for the FFT pic

6) Feed the 20Ms/s real data into Gnuradio 0.9's
atsc_rx.

Voila! The finally screenshot is here: ktvu-The
Loop.jpg


Cheers!

Mao

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