Observations

Pointed Scans

Horizon Scans

Summary

PF1 800 MHz RFI

Observations

On July 7-8, 2004 GBT receiver checkout observations were performed for the PF1 800 MHz band receiver. Serveral scans to identify RFI in the nominal receiver bandpass were made as part of these observations. The spectrometer was used for these observations. The spectrometer was setup to provide 200 MHz instantaneous bandwidths in two separate bandpasses. The two bands had center frequencies of 780 MHz and 820 MHz allowing the whole 800 MHz receiver bandpass to be cover instantaneously.

Pointed observations were made at the Zenith (Az=130, El=90), towards the Jansky Lab (Az=90, El=15) and towards Cheat Mountain (Az=330, El=15).

Horizon scans were taken where the GBT was moved from 0 degrees azimuth to 360 degrees azimuth at a constant elevation of 15 degrees. The telescope was slewed at 30 degrees per minute in azimuth and a 3 second integration time was used.

I have not attempted to calibrate the data. Only raw data from the "cal off" phase is shown.

Pointed Scans

Table 1 provides a quick reference to jump to the desired plot via clicking on the Figure number.

Figure Azimuth Elevation Frequency Range (MHz) Figure Azimuth Elevation Frequency Range (MHz) Figure Azimuth Elevation Frequency Range (MHz)
113090680 - 730 309015680 - 730 5933015680 - 730
213090730 - 780 319015730 - 780 6033015730 - 780
313090780 - 830 329015780 - 830 6133015780 - 830
413090830 - 880 339015830 - 880 6233015830 - 880
513090880 - 920 349015880 - 920 6333015880 - 920
613090680 - 690 359015680 - 690 6433015680 - 690
713090690 - 700 369015690 - 700 6533015690 - 700
813090700 - 710 379015700 - 710 6633015700 - 710
913090710 - 720 389015710 - 720 6733015710 - 720
1013090720 - 730 399015720 - 730 6833015720 - 730
1113090730 - 740 409015730 - 740 6933015730 - 740
1213090740 - 750 419015740 - 750 7033015740 - 750
1313090750 - 760 429015750 - 760 7133015750 - 760
1413090760 - 770 439015760 - 770 7233015760 - 770
1513090770 - 780 449015770 - 780 7333015770 - 780
1613090780 - 790 459015780 - 790 7433015780 - 790
1713090790 - 800 469015790 - 800 7533015790 - 800
1813090800 - 810 479015800 - 810 7633015800 - 810
1913090810 - 820 489015810 - 820 7733015810 - 820
2013090820 - 830 499015820 - 830 7833015820 - 830
2113090830 - 840 509015830 - 840 7933015830 - 840
2213090840 - 850 519015840 - 850 8033015840 - 850
2313090850 - 860 529015850 - 860 8133015850 - 860
2413090860 - 870 539015860 - 870 8233015860 - 870
2513090870 - 880 549015870 - 880 8333015870 - 880
2613090880 - 890 559015880 - 890 8433015880 - 890
2713090890 - 900 569015890 - 900 8533015890 - 900
2813090900 - 910 579015900 - 910 8633015900 - 910
2913090910 - 920 589015910 - 920 8733015910 - 920
Table 1.Table of Figures.




50 MHz Bandwidth Plots at Az=130, El=90

Figure 1. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 680 MHz to 730 MHz.



Figure 2. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 730 MHz to 780 MHz.



Figure 3. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 780 MHz to 830 MHz.



Figure 4. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 830 MHz to 880 MHz.



Figure 5. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 880 MHz to 920 MHz.



10 MHz Bandwidth Plots at Az=130, El=90

Figure 6. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 680 MHz to 690 MHz.



Figure 7. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 690 MHz to 700 MHz.



Figure 8. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 700 MHz to 710 MHz.



Figure 9. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 710 MHz to 720 MHz.



Figure 10. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 720 MHz to 730 MHz.



Figure 11. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 730 MHz to 740 MHz.



Figure 12. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 740 MHz to 750 MHz.



Figure 13. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 750 MHz to 760 MHz.



Figure 14. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 760 MHz to 770 MHz.



Figure 15. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 770 MHz to 780 MHz.



Figure 16. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 780 MHz to 790 MHz.



Figure 17. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 790 MHz to 800 MHz.



Figure 18. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 800 MHz to 810 MHz.



Figure 19. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 810 MHz to 820 MHz.



Figure 20. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 820 MHz to 830 MHz.



Figure 21. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 830 MHz to 840 MHz.



Figure 22. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 840 MHz to 850 MHz.



Figure 23. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 850 MHz to 860 MHz.



Figure 24. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 860 MHz to 870 MHz.



Figure 25. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 870 MHz to 880 MHz.



Figure 26. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 880 MHz to 890 MHz.



Figure 27. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 890 MHz to 900 MHz.



Figure 28. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 900 MHz to 910 MHz.



Figure 29. Click on image for postscript version. 130 degrees Azimuth, 90 degrees Elevation. 910 MHz to 920 MHz.



50 MHz Bandwidth Plots at Az=90, El=15

Figure 30. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 680 MHz to 730 MHz.



Figure 31. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 730 MHz to 780 MHz.



Figure 32. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 780 MHz to 830 MHz.



Figure 33. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 830 MHz to 880 MHz.



Figure 34. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 880 MHz to 920 MHz.



10 MHz Bandwidth Plots at Az=90, El=15

Figure 35. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 680 MHz to 690 MHz.



Figure 36. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 690 MHz to 700 MHz.



Figure 37. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 700 MHz to 710 MHz.



Figure 38. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 710 MHz to 720 MHz.



Figure 39. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 720 MHz to 730 MHz.



Figure 40. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 730 MHz to 740 MHz.



Figure 41. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 740 MHz to 750 MHz.



Figure 42. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 750 MHz to 760 MHz.



Figure 43. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 760 MHz to 770 MHz.



Figure 44. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 770 MHz to 780 MHz.



Figure 45. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 780 MHz to 790 MHz.



Figure 46. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 790 MHz to 800 MHz.



Figure 47. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 800 MHz to 810 MHz.



Figure 48. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 810 MHz to 820 MHz.



Figure 49. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 820 MHz to 830 MHz.



Figure 50. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 830 MHz to 840 MHz.



Figure 51. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 840 MHz to 850 MHz.



Figure 52. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 850 MHz to 860 MHz.



Figure 53. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 860 MHz to 870 MHz.



Figure 54. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 870 MHz to 880 MHz.



Figure 55. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 880 MHz to 890 MHz.



Figure 56. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 890 MHz to 900 MHz.



Figure 57. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 900 MHz to 910 MHz.



Figure 58. Click on image for postscript version. 90 degrees Azimuth, 15 degrees Elevation -- towards Jansky Lab. 910 MHz to 920 MHz.



50 MHz Bandwidth Plots at Az=330, El=15

Figure 59. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 680 MHz to 730 MHz.



Figure 60. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 730 MHz to 780 MHz.



Figure 61. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 780 MHz to 830 MHz.



Figure 62. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 830 MHz to 880 MHz.



Figure 63. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 880 MHz to 920 MHz.



10 MHz Bandwidth Plots at Az=330, El=15

Figure 64. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 680 MHz to 690 MHz.



Figure 65. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 690 MHz to 700 MHz.



Figure 66. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 700 MHz to 710 MHz.



Figure 67. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 710 MHz to 720 MHz.



Figure 68. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 720 MHz to 730 MHz.



Figure 69. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 730 MHz to 740 MHz.



Figure 70. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 740 MHz to 750 MHz.



Figure 71. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 750 MHz to 760 MHz.



Figure 72. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 760 MHz to 770 MHz.



Figure 73. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 770 MHz to 780 MHz.



Figure 74. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 780 MHz to 790 MHz.



Figure 75. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 790 MHz to 800 MHz.



Figure 76. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 800 MHz to 810 MHz.



Figure 77. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 810 MHz to 820 MHz.



Figure 78. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 820 MHz to 830 MHz.



Figure 79. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 830 MHz to 840 MHz.



Figure 80. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 840 MHz to 850 MHz.



Figure 81. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 850 MHz to 860 MHz.



Figure 82. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 860 MHz to 870 MHz.



Figure 83. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 870 MHz to 880 MHz.



Figure 84. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 880 MHz to 890 MHz.



Figure 85. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 890 MHz to 900 MHz.



Figure 86. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 900 MHz to 910 MHz.



Figure 87. Click on image for postscript version. 330 degrees Azimuth, 15 degrees Elevation -- towards Cheat Mountain. 910 MHz to 920 MHz.



Horizon Scans

The images below (Figures 88 and 89) show the raw data for each polarization. These data still contain the receiver bandpass which shows up as the broad (greater than about 5 to 10 MHz) undulations in frequency. Only the brightest RFI show up in these plots.

The bright emission around an Azimuth of 90 degrees is from the Jansky Lab, surrounding buildings and Arbovale. The bright emission around 50 degrees Azimuth is from the area of the 140 Foot Telescope. (Could the 140 Foot area really be a reflection of the Jansky Lab area off of the 140 Foot and into the GBT?)



Figure 88 Click on image for postscript version. X (left) and Y (right) polarizations. 200 MHz bandwidth centered on 780 MHz.



Figure 89 Click on image for postscript version. X (left) and Y (right) polarizations. 200 MHz bandwidth centered on 820 MHz.



Figures 90 and 91 show the data for each polarization where the receiver bandpass has been subtracted. This was done by ordering the data within 25 frequency channels on each side of a point and taking the 10th lowest value as the baseline level for that point. This removes most of the baseline except for areas where the baseline has large gradients - such as the bandpass feature near 817 MHz.



Figure 90 Click on image for postscript version. X (left) and Y (right) polarizations. 200 MHz bandwidth centered on 780 MHz. Baseline has been removed.



Figure 91 Click on image for postscript version. X (left) and Y (right) polarizations. 200 MHz bandwidth centered on 820 MHz. Baseline has been removed.



Figures 92 and 93 show the data for each polarization where the first and last integrations (towards the North) have been linearly interpolated in time and subtracted from the data. These plots best show directions from which low-level, broad-band RFI is orginating.



Figure 92 Click on image for postscript version. X (left) and Y (right) polarizations. 200 MHz bandwidth centered on 780 MHz. Data has had all emission from the North subtracted from the whole data set.



Figure 93 Click on image for postscript version. X (left) and Y (right) polarizations. 200 MHz bandwidth centered on 820 MHz. Data has had all emission from the North subtracted from the whole data set.



Summary

Many RFI frequencies exist in the PF1 800 MHz bandpass. The best area for observations appears to be between 801 MHz and 850 MHz. RFI definitely increases towards the Jansky Lab and the surrounding residential areas.

The vast majority of the RFI in this scan is due to UHF TV stations (below 806 MHz), Airphones and cellular control towers in the 869-894 MHz range. These signals originate from outside the NRQZ. The favorable range of 801 MHz - 850 MHz is due primarily to the lack of cellular phone handsets (824-849 MHz) and the non-use of a couple other allocations in this range in the vicinity of the observatory. Note that a virtual absence of RFI in the plots 49 - 51, which were taken with the GBT pointed in the direction of the Jansky Lab, reinforces this theory. It is likely that the apparent directionality in some of the plots is due to gaps in our terrain shielding. Note that our horizon is actually below the horizontal in one direction and close to the horizontal in a few others.

The Airphone RFI tends to dominate the RFI scene when present. It has on occasion been 20 to 40 dB above the noise floor. The Airphone allocations are in the range 894 to 896 MHz and can clearly be seen in Figure 85.

Below is some additional detail about the allocation of the spectrum from 806 to 902 MHz:

  • 806-821 MHz - Non-government allocation for Fixed/Land Mobile transmitters. Used by SMR mobiles.
  • 816-820 MHz - Non-government allocation for Basic Exchange Telephone Service. Paired with 861-865 MHz.
  • 821-824 MHz - Non-government allocation for Land Mobile (Mobile-to-Base) transmitters. Used by Public Safety providers.
  • 824-849 MHz - Non-government allocation for Fixed/Land Mobile transmitters. This is the band used by Cellular Mobiles.
  • 849-851 MHz - Non-government allocation for Aeronautical Mobiles. This is one of two bands used by Airphones.
  • 851-866 MHz - Non-government allocation for Land Mobile transmitters. This is the band used by SMR base stations.
  • 866-869 MHz - Non-government allocation for Land Mobile (Base-to-Mobile) transmitters. Used by Public Safety providers.
  • 869-894 MHz - Non-government allocation for Fixed/Land Mobile transmitters. This is the band used by Cellular Base Station.
  • 894-896 MHz - Non-government allocation for Aeronautical Mobiles. This is one of two bands used by Airphones.
  • 896-901 MHz - Non-government allocation for Fixed/Land Mobile (Mobile-to-Base) transmitters.
  • 901-902 MHz - Non-government allocation for Personal Communications (narrowband PCS) transmitters.

  • Last modified: Tue Jul 27 13:17:23 EDT 2004