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"Mid-week" RFI in 16cm band

Posted: Wed Mar 23, 2011 4:49 pm
by ste616
You may have heard people talking about something called "mid-week RFI" that affects ATCA data in the 16cm band (spanning 1.1 - 3.1 GHz). This RFI has a very distinctive signature that is fairly easy to see during observations or reduction.

There are two main lines that will appear very strong, with frequencies near 1265 MHz and 1310 MHz. With a normal centre frequency of 2100 MHz, these lines will appear at channels 1860 and 1815 respectively (the 16cm band is inverted), and each line will be about 10 MHz wide. Below is a plot covering the channels 1600 to 2000 of a normal 16cm observation while the mid-week RFI was visible.
midweek_rfi_16cm.jpg
midweek_rfi_16cm.jpg (70.03 KiB) Viewed 42240 times
This doesn't seem to only affect those channels though, as the entire spectrum appears to get quite ugly when this RFI is present, as seen below.
lotsarfi_16cm.jpg
lotsarfi_16cm.jpg (72.71 KiB) Viewed 42240 times
When this RFI is not present, the spectrum (at the same scale) looks rather more useful:
norfi_16cm.jpg
norfi_16cm.jpg (51.63 KiB) Viewed 42240 times
If you see this RFI, you are encouraged to report it by submitting a Fault Report, including the time you saw it, and for how long it affected you. It is a good idea to do this for any RFI you feel is causing you difficulty, at any frequency.