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.

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

    The rms/mean by channel was computed for each strip taken by a2010 (998 strips)  between 01may05 and 09jun05 (this is part of the monitoring of a2010 data). If there is rfi in a frequency channel then the rms/mean will be larger than the radiometer equation dictates. The rms/means for each strip were put together into an image to see when the 1428 Mhz birdie was active.     The 1428Mhz problem started around strip number  370 (18may05) and lasted till strip number 610 (about 23may05). After this it did not appear again (at least through 09jun05). There is a narrow birdie (not resolved in 50Khz channels after hanning smoothing) and a wider birdie (about 250 khz wide) centered at 1427.8 Mhz. When looking at the narrow birdie on the spectrum analyzer, it looked like two birdies separated by about 30 khz. The birdies appear in all pixels and both polarizations.

    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).

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

    The 1428Mhz biridie was strongest on 21may05 in the strip with scannumber 514184839. The images below are dynamic spectra for this strip. The image is for pixel 3b where it was strongest. The power in the birdie frequency channel versus time (.ps) (.pdf)  for the strip with the strongest birdie.


processing: x101/050524/chkrfi.pro