1428 Mhz birdie in alfa

        Project a2010 (alfalfa) does 600 second  drift scans dumping once a second using 100 Mhz centered at 1385 Mhz.  A birdie a 1428 Mhz appeared on 18may05 and remained until 23may05. It was not seen after that (looking at data through 09jun05). The a2010 data was examined to characterize the birdie.

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Using the rms/mean for each strip to see when the birdie was active.

• Image of (rms/Mean by scan) vs freq for may05 thru 09jun05 (.gif): The is of pixel 0 polA.
• Blowup in frequency (rms/Mean by scan) vs freq for may05 thru 09jun05 (.gif): This is a blowup in frequency of the first image.

    The next set of plots takes the rms/mean for the frequency channel of the narrow birdie and divides it by the adjacent channels (so that 1 --> the expected rms/mean for the bandwidth , integration time).
Normalized rms/mean of the narrow band birdie (1428.24 Mhz)  for all strips(.ps) (.pdf).

• The top figure shows the normalized rms/mean of this channel for 01may05 thru 09jun05 (note that the major tick marks  are placed at 12:noon of the day since they are julian days). On the 18may05 the rms/mean increases and stayed elevated till 23may05. On 21may05 one strip had the rms/mean for this channel 1400 times the expected value.
• The middle and bottom figures are blowups of the strength so you can see when the problem started and ended.

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Looking at the strip where the 1428 mhz birdie is strongest.

• Dynamic spectra 21may05  scan 514184839 pixel 3b (.gif):  The 1428 birdie is there for most of the 600 seconds. It does not seem to affect the channels far from its frequency.
• Blowup of dynamic spectra 21may05  scan 514184839 pixel 3b (.gif):  This is a blowup in frequency of the above dynamic spectra. You can see that the wider birdie at 1427.76 is correlated with the 1428.24 Mhz birdie. Sample 376 is where the peak occurs.

• The top figure plots the power in frequency channel 1428.24 for scan   514184839.  The birdie increased to about 240 times Tsys near second 370 of the strip.
• The bottom figure blows up the vertical scale. The birdie has a value larger that Tsys for the entire strip (tsys=1).  The images of the dynamic spectra do not show this since they normalize each frequency channel of the image to the median value.

Summary:

• A birdie appeared at 1428.24 Mhz on 18may05 and stayed until 23may05. It was less than 50 Khz wide. It's strongest value was 240 times tsys on 21may05.
• A wider birdie (about 200Khz)  was also present at 1427.76 Mhz.
• The birdie did not affect the spectra more than a mhz away.
• When looking at the 1428.24 birdie on the spectrum analyzer it looked like there were two narrower birdies separated by about 30khz. On the radio there was a hum (i'm not sure what frequency) but no other identifiable modulation.
• The narrow birdie was relatively stable in frequency.
• The birdie disappeared before we could do any more troubleshooting.