On Thursday, July 01, 2010 11:35:13 am Marcus D. Leech wrote: > Oh, I agree that it's in the tradition of Gnu Radio filters. It's just > that after you've finished reading > paper after paper about FFT filters for de-dispersion, with everything > being expressed in the > frequency domain, it's a bit jolting to find that the FFT filter takes > "taps" in the time-domain.
The old way with hardware was a massive filter bank; we have an old hardware de-dispersion machine here that isn't working at the moment. Given that dispersion produces a 'chirp' from a pulse, de-dispersion is essentially de-chirping, and providing programmable delay per band. But a low DM pulsar shows up very well on a waterfall display. Or to put it exceptionally bluntly, the frequency domain doesn't really exist anyway, as all signals are in the time-domain to begin with. Even hardware filters act on the time domain signal to produce a frequency domain result, whether they are lumped constant LC or RC filters or distributed constant cavities. But yes I sympathize with your mind-bending there, Marcus. Much like the mind-bending required when dealing with audio feedback; it doesn't seem to make sense that the amount of feedback doesn't change the amplitude of the end oscillation, but rather the amount (and phase) of feedback determines the frequency of the oscillation. And due to the acoustics of some venues, there is actually a 'sour' spot on the volume level where the feedback is worse, and goes away when the level is turned up (not down, but up). Counterintuitive, but definitely a real effect. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
