Thanks, Marcus. I'm okay with not doing real-time, as long as I don't lose a ton of data. I'm only going to be running for about 30 seconds at a time.
On Tue, Nov 19, 2013 at 6:36 PM, Marcus D. Leech <mle...@ripnet.com> wrote: > On Tue, Nov 19, 2013 at 7:19 PM, Paul B. Huter<paul.b.hu...@gmail.com> >> wrote: >> >>> I recall that that was what you had mentioned yesterday, but could you >>> explain why setting it to 15M will allow me to grab 30M? >>> >> Sure. >> >> We're working at complex baseband. The signal you capture at 50 Msps >> will be observable from -25 MHz to +25 MHz. Because it's a complex >> signal, we have both sides around 0 Hz; also, it means that for a 50 >> Msps sampling rate, we can "see" 50 MHz of bandwidth. >> >> So to get the middle 30 MHz, you want to define a filter that extends >> from -15 to +15 MHz. A low pass filter is a real-valued signal. We >> define it from 0 to 15 MHz, but because it's real, it's symmetric >> around 0 and thus extends from -15 to +15 MHz. >> >> Also, be careful about using 1000 Hz as your transition band. That's >> still going to generate a gigantic filter. Using a 100 kHz transition >> band with a 50 Msps sampling rate produces a filter 909 taps long, >> which is very, very long. >> >> Use gr_filter_design (launched from the command line) to design a >> filter that's suitable. You can probably get away with a transition >> band of 1 MHz. >> >> Tom >> >> You can actually be fairly "sloppy" with the width of the transition > bands and still produce a pretty-good filter. For 50Msps sample > rate, I'd use a 5-10MHz transition bandwidth. Also, if you're really > sampling at 50Msps, you'll not be able to do much in real-time > before your computer falls-over. > > > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortium > http://www.sbrac.org > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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