USRP Custom Filter Taps

GNU Radio
1

I am working on an NTSC receiver using the USRP/TVRX board. I am tunning
the board to 63.25 MHz with decimation set to 10; this gives me 6.4 MHz
of bandwidth. The NTSC channel is 6 MHz wide so with these settings I
get some interference from the adjacent channels.

Is there a way to set the filter taps used by the USRP so that I could
make a filter to remove the frequency infomation at the extreme right
and left of the sampled data? I can use an FIR filter in the PYTHON
runtime but it uses lots of CPU power.

I read on a previous thread that it is possible to invert the spectrum
of the sampled signal so that the tuned frequency would be the FM
carrier. The end result being a stream from the USRP where 0 Hz is the
center frequency of the audio carrier the the video carrier is at 4.5
MHz. Is this possible? The advantage here is that the baseband audio
does not need to be shifted before fm demodulation; also the video
carrier does not need to be shifted before demodulation (AM).

Regards,
Daniel

2

Daniel G. wrote:

I am working on an NTSC receiver using the USRP/TVRX board. I am tunning the board to 63.25 MHz with decimation set to 10; this gives me 6.4 MHz of bandwidth. The NTSC channel is 6 MHz wide so with these settings I get some interference from the adjacent channels.

Is there a way to set the filter taps used by the USRP so that I could make a filter to remove the frequency infomation at the extreme right and left of the sampled data? I can use an FIR filter in the PYTHON runtime but it uses lots of CPU power.

Yes, you can change the filter taps in the FPGA. See the halfband (HB)
verilog code.

I read on a previous thread that it is possible to invert the spectrum of the sampled signal so that the tuned frequency would be the FM carrier. The end result being a stream from the USRP where 0 Hz is the center frequency of the audio carrier the the video carrier is at 4.5 MHz. Is this possible? The advantage here is that the baseband audio does not need to be shifted before fm demodulation; also the video carrier does not need to be shifted before demodulation (AM).

Not sure what you’re looking for here.

Matt