Sysquick Plots

VLA "SYSQUICK plots" are made by combining a series of standard spectral line observations across the bands of interest. Data is collected using either the entire array, or (as in the case of L band) a sub-array of 5 or 6 antennas. The antennas are pointed near the celestial north pole, so terrestrial interference may be assumed to be entering in the antennas' side-lobes. Another advantage of using a "source" near the celestial north pole is the fact that terrestrial interference (what we are looking for with these observations) will be more likely to correlate when the antennas are all pointed at a nearly stationary point in the sky.

At each frequency sub-band, the data is integrated and cross-correlated for 10 seconds, then written to disk. From 3 to 6 such collections are performed at each frequency before shifting up to the next frequency. For the C, X, U, and K band low (spectral) resolution observations, the instantaneous bandwidth is 12.5 MHz, and the frequency step size is 10 MHz, leaving an overlap of 2.5 MHz, or 1.25 MHz on each end of the scan spectra. The overlap allows us to throw out the band edges during the plotting process, so as to produce a smoother looking spectra when all the scan plots are combined. For the P and L band high resolution observations, the instantaneous bandwidth is 1.5625 MHz, and the frequency step size is 1.25 MHz.

For all bands except P-band and L-band, the plot frequency resolution is around 400 KHz (12.5 MHz IF bandwidth/32 channels). For P and L bands, the plot resolution is around 6 KHz (1.5625 MHz IF bandwidth/256 channels). The data for the low resolution plots are correlated using the VLA "2AB" mode. For P band, the correlator is set for the "1A" mode. For L-band, the correlator is set for either the "1A" or the "1B" mode, depending on which of the 4 sub-band regions and sub-arrays are being run. For the P and L band observations, Hanning smoothing is applied during the correlation process in order to reduce the ringing (Gibbs effect) from very strong "spikey" RFI signals. Each plot shows the log of the spectral power flux density vs. frequency for the entire band, with "Power Flux Density" (spectral power flux density) being measured in Janskys (1 x 10^-27 W/m^2/Hz).

The standard bands surveyed (on an irregular basis) are P, L, C, X, U, and K bands. The SYSQUICK RFI surveys cover the follow frequencies in each band. For each band, the number to the right (in parenthesis) represents the VLA "band edge":

			(MHZ)			(MHZ)
  P-band		  300	  (308)		  350	  (340)
  L-band		 1220	 (1350)		 1760	 (1730)
  C-band		 4590	 (4500)		 5000	 (5000)
  X-band		 8340	 (8000)		 8610	 (8800)
  U-band		14400	(14400)		15400	(15400)
  K-band		22000	(22000)		22600	(24000)

The SYSQUICK RFI survey observations are generally made during VLA "double maintenance days", once per month. Observations may be scheduled in for any time of the day or night, depending on the availability of time. Depending on how many bands are surveyed, the new data should be available in from 1 to 2 weeks after the observation.

Modified on Friday, 26-Sep-2008 12:09:34 MDT by Stephan Witz