Re: [Discuss-gnuradio] USRP Custom Filter Taps
On Thu, Oct 05, 2006 at 05:51:49PM -0700, Daniel Garcia wrote: Matt Ettus wrote: Yes, you can change the filter taps in the FPGA. See the halfband (HB) verilog code. Thanks! I'll take a look. 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 base-band 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. After thinking about it, I'm not sure either. I figured I can to tune to FM carrier to the center frequency (0Hz), set the decimation to 4 (16 MS) and the video carrier is at -4.5MHz. Unfortunately, my USB/computer can't handle can't handle the 16 MS rate. I was hoping to avoid translating the signal by placing the FM signal at 0Hz. Since my PC can't handle that data rate, I'm just going to concentrate on the NTSC. -Daniel As an aside: It would be nice to have something like the GC4014 on-board the USRP. In my application it could be used to tune the video and audio signals on separate receiver channels without using up resources on the PC (and also reduce the need for a faster interface in some cases). Not sure if there's enough room on the FPGA though. The cost of extracting and decimating the audio portion of the full signal in s/w is pretty small. Have you tried just setting decimation to 8 giving 8MS/s complex? Why are you concerned about anything at 16MS/s? The 8 MS/s signal will have both the audio and video in it. A small amount of filtering would separate the two streams in software. Eric ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] USRP Custom Filter Taps
Daniel Garcia 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 ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] USRP Custom Filter Taps
Matt Ettus wrote: Yes, you can change the filter taps in the FPGA. See the halfband (HB) verilog code. Thanks! I'll take a look. 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 base-band 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. After thinking about it, I'm not sure either. I figured I can to tune to FM carrier to the center frequency (0Hz), set the decimation to 4 (16 MS) and the video carrier is at -4.5MHz. Unfortunately, my USB/computer can't handle can't handle the 16 MS rate. I was hoping to avoid translating the signal by placing the FM signal at 0Hz. Since my PC can't handle that data rate, I'm just going to concentrate on the NTSC. -Daniel As an aside: It would be nice to have something like the GC4014 on-board the USRP. In my application it could be used to tune the video and audio signals on separate receiver channels without using up resources on the PC (and also reduce the need for a faster interface in some cases). Not sure if there's enough room on the FPGA though. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] USRP Custom Filter Taps
As an aside: It would be nice to have something like the GC4014 on-board the USRP. In my application it could be used to tune the video and audio signals on separate receiver channels without using up resources on the PC (and also reduce the need for a faster interface in some cases). Not sure if there's enough room on the FPGA though. That's essentially what is in the FPGA. There are 2 DDCs in the standard build, and 4 in the RX-only build. Each can be tuned to different ADCs, or to the same ADC to get separate bands from the same stream. Matt ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
[Discuss-gnuradio] USRP Custom Filter Taps
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 ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
