Drifting RFI, part deux

Message boards : Nebula : Drifting RFI, part deux
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Profile David Anderson
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Message 1848121 - Posted: 11 Feb 2017, 22:19:06 UTC

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%.
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Message 1848560 - Posted: 13 Feb 2017, 20:57:37 UTC - in response to Message 1848121.  

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...)
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Message 1851931 - Posted: 27 Feb 2017, 22:00:46 UTC - in response to Message 1848560.  

thank you very much!
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Message boards : Nebula : Drifting RFI, part deux


 
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