Drifting RFI, part deux

Message boards : Nebula : Drifting RFI, part deux
Message board moderation

To post messages, you must log in.

Profile David Anderson
Volunteer moderator
Project administrator
Project developer
Project scientist

Send message
Joined: 13 Feb 99
Posts: 171
Credit: 502,653
RAC: 0
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%.
ID: 1848121 · Report as offensive
wulf 21

Send message
Joined: 18 Apr 09
Posts: 93
Credit: 26,337,213
RAC: 43
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...)
ID: 1848560 · Report as offensive

Send message
Joined: 27 Feb 17
Posts: 3
Credit: 0
RAC: 0
Message 1851931 - Posted: 27 Feb 2017, 22:00:46 UTC - in response to Message 1848560.  

thank you very much!
ID: 1851931 · Report as offensive

Message boards : Nebula : Drifting RFI, part deux

©2022 University of California
SETI@home and Astropulse are funded by grants from the National Science Foundation, NASA, and donations from SETI@home volunteers. AstroPulse is funded in part by the NSF through grant AST-0307956.