Gr-atsc related question

GNU Radio
1

Hi,
I am new to gnu radio/usrp. I am trying out digitial
TV application gr-atsc. I have a USRP N210 with a
basic omnidirectional antenna.
I checked local digital TV stations and found (from Internet) that
there is one at 603.25 MHz (UHF channel 36) and the station is
listed to be about 14 miles from here. When I run
uhd_fft to receive the channel, I do not see any signal.
I used a hardware oscilloscope to scan the UHF band, but could
not find signal anywhere. Could it be because I do not have a
good antenna (I have only basic omnidirectional antenna which
looks like a 0.75 foot rod; sorry I do not have much communication
engg background).
Now, even without any TV signal, should the gr-atsc application
Work? It is ok if it shows me a black screen from the mpeg file.
But when I run the five python scripts (interp_short.py, xlate.py
etc.),
The mpeg file generated is of zero size. So I modified the python
scripts
to write to file (instead of fifo). What I found was that after runnin
“btl-fsd-py”, its output file is of size zero (other scripts before it
generate
file of huge size). What is the problem here?

Thanks.
-Anirudh

2

On Fri, Sep 14, 2012 at 5:41 PM, Sahoo, Anirudha
[email protected] wrote:

there is one at 603.25 MHz (UHF channel 36) and the station is

The mpeg file generated is of zero size. So I modified the python scripts
Thanks.

-Anirudh

Anirudh,

If you can’t see a signal and there is nothing to demod, then the mpeg
file size should be zero. ATSC has digital frames that are used in
locking and syncing with the signal. If the receiver can’t find these
bits, it has no idea how to frame the mpeg, so it doesn’t produce
anything.

What kind of daughter board are you using with your USRP? Have to
adjusted the gain to see if that helps? Any other stations around you
that you can try, instead? You should also be able to find a ATSC
amplifier that you can put between your antenna and USRP if you are
still having trouble getting a signal.

Tom

3

Thanks Tom for the prompt and helpful reply.
I am using SBX 400-4400 MHz Rx/Tx daughterboard.

From: [email protected] [[email protected]] On Behalf Of Tom
Rondeau [[email protected]]
Sent: Saturday, September 15, 2012 10:46 AM
To: Sahoo, Anirudha
Cc: [email protected]
Subject: Re: [Discuss-gnuradio] gr-atsc related question

On Fri, Sep 14, 2012 at 5:41 PM, Sahoo, Anirudha
[email protected] wrote:

there is one at 603.25 MHz (UHF channel 36) and the station is

The mpeg file generated is of zero size. So I modified the python scripts
Thanks.

-Anirudh

Anirudh,

If you can’t see a signal and there is nothing to demod, then the mpeg
file size should be zero. ATSC has digital frames that are used in
locking and syncing with the signal. If the receiver can’t find these
bits, it has no idea how to frame the mpeg, so it doesn’t produce
anything.

What kind of daughter board are you using with your USRP? Have to
adjusted the gain to see if that helps? Any other stations around you
that you can try, instead? You should also be able to find a ATSC
amplifier that you can put between your antenna and USRP if you are
still having trouble getting a signal.

Tom