Anish Roshi, Jeff Acree & Ron Maddalena (June 07, 2002)
Results of the Radio Frequency Interference (RFI) measurements made on June 03, 2002 in the 510--690 MHz frequency band of the GBT are described in this note. The measurements were done to compare the RFI status in this band with the data taken on January 15, 2002 ( RFI status report Jan1502 ). Unlike the observations on January 15th, all the data for the present measurement were taken with the antenna positioned at Az = 44 deg and El = 54 deg. The data acquisition, analysis and other details are same as those given in RFI status report Jan1502 . Increased RFI is seen in the frequency range 566 -- 572 MHz and 602 -- 608 MHz when compared with the earlier data. Whether this increased RFI is due to a new interference source needs to be confirmed by further measurements since RFI is time variable.
Fig. 1 shows raw spectrum averaged over 120 sec (top) from one of the linear polarizations (labeled as XX in the data header) and band-shape corrected spectrum (bottom) at the time (in UT) indicated on the title. The frequencies of the RFI components picked up by an automatic RFI detection glish routine (see RFI status report Jan1502 ) are in the file rfi600june0302.freq .
Fig. 2 shows band-shape corrected spectra averaged over 8 minutes from one of the linear polarizations (XX). The frequencies and relative amplitudes of the RFI components picked up by an automatic RFI detection glish routine are in the file avrg600june0302.freq . Comparison of the average spectrum with that obtained on January 15 indicates that increased RFI emission is present in the frequency range 566 -- 572 MHz and 602 -- 608 MHz.
Fig. 3 shows the gray scale display of the 4 spectra on each 40 MHz band taken over 3 hrs. As seen in the earlier data much of the narrow band RFI is present throughout the observations. The increased RFI emission near 570 MHz is present in the entire data, but the RFI near 605 MHz is present only in the last two spectra.