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Nebula :
Drifting RFI, part deux
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David Anderson Send message Joined: 13 Feb 99 Posts: 173 Credit: 502,653 RAC: 0 |
The drifting RFI algorithm I added recently (an adaptation of the one used for decades by SERENDIP) was effective for removing drifting RFI. However, it also removed about 90% of all the other signals. Recall that the algorithm works as follows: for each signal, we look at 6 radial sectors in time/freq space, going forward in time with different slopes (corresponding to different ranges of drift rate). If any sector has a number of signals that exceeds a threshold, its contents are marked as RFI. Using the RFI browsing tools I described in the last post, I explored several examples of this, and found that there were two problems: 1) Spikes often occur in "clusters": 5-10 spikes at almost the same time and freq. If there was a signal somewhat before this, at a close freq, the sector containing the cluster would exceed threshold and all the spikes would (erroneously) get thrown out. 2) Where there is narrow-band RFI (drifting or not), signals within a few 1000 Hz were getting thrown out because one of the oblique sectors from that point would include some of the RFI. Eric Korpela and I spent some time discussing these problems. In the end, the following seemed to work in the cases I looked at: - For 1), identify clusters (+/- 1Hz, +/1 1 sec) and treat them as 1 signal. - For 2), change the RFI algorithm parameters to: #sectors: 11 threshold: 1e-4 max drift rate: 5 With these changes, the drifting algorithm still removes the target RFI, and the fraction of spurious removals is down to < 1%. |
wulf 21 Send message Joined: 18 Apr 09 Posts: 93 Credit: 26,337,213 RAC: 43 |
Thanks for the updates. Really appreciating that we can actually see how things are moving forward (and even kind of touch and touch and try out...) |
gogejany142 Send message Joined: 27 Feb 17 Posts: 3 Credit: 0 RAC: 0 |
thank you very much! |
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