Several RFI signals appear on this recent data that did not happen in the previous week, when the laser systems were on. Signals at some of the same frequencies as the previous week appear at drastically different power levels. In view of the apparent variable nature of many of the sources of RFI, we cannot definitely associate any signals with the laser systems. A better approach to identifying RFI from the laser systems might be to switch the lasers on or off every hour, doing a spectrum sweep in between. Another approach would be for the IPG to track down the various RFI peaks that have been identified in this survey.
Figure 1. Plot of all data from Feb 7-8, averaged.
Figure 2. Zoomed plot.
Figure 3. Filtered and normalized plot. (See Results section below for more details.)
The major RFI features are the same as in the previous survey. Refer to the previous writeup for plots. The directional nature of the signals is also similar.
To compare the results from the Jan 30 data with the present data, a plot of the difference in the filtered data is shown in Figure 4 and Figure 5. See further discussion below in the results section.
|Table 1: Observations 08 Feb 2002, project: rfi_S_feb07|
|Scan #s||Start Time (UT)||Azimuth (deg)|
The spectrum is again dominated by the satellite RFI in the range 2320 to 2345 MHz. Weaker features can be seen in Figure 2, plotted with an expanded scale.
Again, we note that the noise level is much higher in X polarization (red plot) that in Y (green) at frequencies where the strong satellite RFI is in or near the band.
Figure 3 shows the filtered averaged over all scans: the X polarization is shown in red, Y in green. Again, the spectrum is cleaner for frequencies less than 2200 MHz in the Y polarization.
The list of RFI peaks based on the data plotted in Figure 3 is given in Table 2. All peaks exceeding 1.002 are listed in Table 2, omitting those between frequencies of 2485-2500 and 2315-2347 MHz. The power (P) in Table 2 is the y-coordinate transformed to 0.001 units above 1.0; i.e., P = 1000(Y-1). i.e., the power is in parts per thousand of the system temperature. The maximum of the 2 polarizations is listed.
Note particularly strong RFI around 2460-2470 MHz, and at 2200 MHz, that was not very notable in the Jan 30-31 data. Close-up plots of these features in the raw data are shown in Figure 6A and Figure 6B.
Inspection of these plots suggests there was more and stronger RFI on the latter date than the former.
We have listed tables of RFI components from the difference spectra. Table 3 are the components that were stronger on Jan 30-31, and Table 4 lists those stronger on Feb 7-8. Amplitudes are listed in units of 0.001 of the system temp. The tables list all components exceeding 0.002 of the system temp.
Again, most of the RFI seems associated with the az=96 spectrum, i.e., in the general direction of the Jansky Lab. In particular the very strong features at 2200 MHz and 2467 MHz seem associated with this direction.