180212 100ms rfi

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   Data taken 12feb18 showed 100ms periodic rfi spanning 2388-2390 MHz.

Setup:

• Data was taken with the mock spectrometer using 4096 channels and 2.048 ms spectral dumps
• 5 scans were taken:
• file 300: sbn: cfr 2390 MHz, bw=20MHz, 750nb mixer, 16 bit sampling, 67 seconds of data
• file 500: sbn: cfr 2380 MHz, bw=40MHz, 750nb mixer, 32 bit sampling
• file 600: sbn: cfr 2380 MHz, bw=80MHz, 750nb mixer, 32 bit sampling
• file 700: sbw:cfr 2380 MHz, bw=80 MHz, 750nb mixer, 32 bit sampling, 2040 to 2400 rf filter
• file 800: sbw: cfr 2380 MHz, bw=80 MHz, 750    mixer, 32 bit sampling, 2040 to 2400 rf filter

dynamic spectra were made using  485 spectra (.99238 secs) of data

file	dynamic spectra
300, sbn 2390MHz,bw 20mhz	.gif
500, sbn 2380 MHz,bw 40 MHz	.gif
600, sbn 2380 MHz, bw 80MHz	.gif
700, sbw 2380 MHz, bw 80MHz	.gif
800, sbw 2380 MHz , bw 80MHz, 750mixer	.gif

 

• The rfi was seen in sbn and sbw.

The images show polA (which was stronger than polB)

• Some of the spectra is more cut off at the higher end because of the filters.
• The period looks close to 100 ms.

Plots of spectra at 100 ms peak (.ps) (.pdf)

• The 5 frames are the 5 separate files
• Each frame holds a 2.048 ms spectra when the 100 ms rfi was strongest
• the first frame (file 300) saturated. it only used 16 bit spectra. The other 4 spectra used 32 bit spectra.
• The 3 colors are 3 spectra around the peak:
• black: 2.048 ms before peak
• red : at peak
• green: 2.048 ms after peak.
• The spectra have been normalized to the spectral band 2380-2385.

Spectra of the total power 2389-2398 MHz (.ps) (.pdf)

• For each file, the total power  between 2389 and 2398 MHz was computed.
• the magnitude of the tp spectra was then plotted (abs(fft(tp))
• A comb of harmonics is show going out to about 240 hz
• Black is polA, red is polB.
• The first file had 67 seconds of data, the other 4 files had less data.
• for file 300, the 24th harmonic was measured to be 234.372 hz
• dividing by 24 gives the fundamental as 9.7655Hz (period .1024012 secs)
• So the period is not exactly 100 ms.

SUMMARY:

• periodic rfi was seen with sbn and sbw
• the period was .1024 seconds
  

processing: x101/180212/sbn100msrfi.pro