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Re: [Discuss-gnuradio] porting ATSC to 2.x and USRP

From: Martin Dvh
Subject: Re: [Discuss-gnuradio] porting ATSC to 2.x and USRP
Date: Wed, 22 Mar 2006 05:15:59 +0100
User-agent: Debian Thunderbird 1.0.2 (X11/20051002)

mao mao wrote:
> Sounds good!
> I am still not convinced that USRP can handle ATSC
> demodulation. Please tell me how are you gonna recover
> the carrier with 16Ms data and 4MHz IF? If this
> problem can be solved, the rest are pretty easy.
The usrp gives you 8Mhz bandwidth which should be enough for atsc
The atsc channelwidth is less then 8 Mhz.

One quick and dirty solution is to interpolate to 32 Mhz in stead of 16 Mhz 
before the atsc real code.

for example
input is 8 Msps complex which corresponds to -4Mhz to 4Mhz with centre of 
channel at 0 Mhz
interpolate to 32 Msps
multply with 5.75 Mhz complex sine
complex to real

Now you have a 32 Msps real signal with IF at 5.75 Mhz
now you can multiply with the 1.31MHz NCO and use lowpass filter to get rid of 
the high mirror.

The better way of doing this is to stay with complex samples all the way into 
the pll of the atsc code
Then you don't need any filtering. But this would be a future enhancement.

> The reason why I want to buy a working mc4020/mt4937
> combo is that I want to play with REAL HDTV data. This
> is way more exciting than playing with the test data.
I totally agree.
For me this is not possible because I live in europe (no atsc signals).
So I have to implement DVB-T, DVB-S or DVB-T in gnuradio to play with digital 
I probably wait until the atsc code starts working to use this as an example 
for DVB (a lot of components are similar)

> If you can recover the atsc carrier with USRP, I can
> finish the rest of atsc code real quick
The carrier can be recovered, so please do this.

I am also working an a live TVscreen sink for gnuradio (using SDL).
It is already in cvs (gr-video-sdl), but it is work in progress so the API 
hasn't stabalized yet.

> --- Eric Blossom <address@hidden> wrote:
>>Here's a proposal: if you, Rafael, or anybody else,
>>get the rest of
>>the code ported (following the outline about the
>>loopback tests in the
>>previous message), I will ensure that the FPLL is
>>modified to work
>>with complex baseband from the USRP.
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