On Tuesday 19 April 2005 10:54, n4hy wrote: > Cascaded Integrator Comb filters are pretty simple filters that are very > fast to compute > but produce those slow roll offs. There are more complex things that > could be done and > hopefully now that the USRP is really flowing out the door, > daughtercards and all, and > as we come up to speed, we can work on these subtleties in the core code.
Yeah, we're trying to apply these as spectrometers at PARI, and getting a flat baseline is pretty much required. I personally am working on spec-an stuff for AM broadcast (to do 47CFR73.44 occupied bandwidth measurements, where 12 bit resolution is fine). For the spectrometer project, we don't actually want an FFT. We want a swept filter analyzer instead, for integration purposes. FFT is acceptable, but most radio astronomy spectrometers are swept filter. Getting swept filter in software isn't too hard, either, but pre-filtering with the FPGA would be nice, then set up the software filters as fixed-frequency. The skirts next to signals are quite curved, too, and make the box not as useful as it could be in my application. Straight A/D at a low enough sample rate to get over the USB with no filtering at all I could deal with, but I've not dug into the code deep enough as yet to see how that works. I can choose basically any IF I want, and 10.7MHz is fairly standard in the RA world, which falls in the passband of the USRP nicely. My personal USRP I ordered with a TVRX (plus a BasicTX/RX pair), and I must say the WFM demod is nice for UHF NTSC TV audio. I see the BTSC stereo subcarriers properly, and can even see some hsync leakage in the audio. I may also write an NTSC block; I do enough video work that having a vectorscope and a waveform monitor is required. Currently I drag around an SGI O2 with the analog video card; the SGI diagnostic software for that card has vectorscope and waveform monitor capabilities. Does anyone (Matt?) have a good characterization of the frequency response curves of the BasicRX? If not, I'll take our calibrated noise sources and generators here and produce one; but it will be offset by the curvature already noted. -- Lamar Owen Director of Information Technology Pisgah Astronomical Research Institute 1 PARI Drive Rosman, NC 28772 (828)862-5554 www.pari.edu _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
