Documentation
glangsto -at- nrao.edu created on: 2003SEP15
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RFI in the 280-390 MHz band.
Comparision of RFI before and after addition of active surface RFI shielding.
The 300 MHz band was surveyed for RFI on 2003 May 01, before
adding the RFI shielding on the active surface. After installation
of the active surface shielding, another RFI search was performed.
The active surface shielding is effective. The brightest
RFI lines remaining are at frequencies corresponding to Cable TV
video and audio signals.
Activer Surface RFI
The first three plots below show three 50 MHz bands centered
on 285, 325 and 365 MHz. These data are calibrated assuming a
system temperature of 70 K. The periodic 2. MHz RFI spikes
are clearly visible. A band pass filter excludes RFI below 280 MHz
and above 365 MHz.
Activer Surface Filtered
The second set of plots show three 50 MHz bands centered on 290, 330 and
370 MHz. These data are calibrated assuming a system temperature of 70K.
The 2 MHz spaced spikes are gone, but spikes corresponding to
cable TV channels remain. No band pass filter is inserted in the
system, so all RFI in the band is visible.
Powering Active Surface Off
To confirm the effectiveness of the shielding, the active
surface motor driver circuits were powered off. Spectra were
obtained before and after power down. The high variabilty of the
RFI in this band makes comparison difficult.
Data are in Green Bank Telescope project directories 'T_PF1_03MAY01'
and 'TGBT01A61_01'.
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3C286: 2499; OffOn 1/2
No active surface shielding
Samp 1,3/4, State 1-2/2, Ave of 6 Int.
Ascii Data (2003_05_01_23:06:53A.1.log)
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3C286: 2499; OffOn 1/2
No active surface shielding
Samp 2,4/4, State 1-2/2, Ave of 6 Int.
Ascii Data (2003_05_01_23:06:53A.2.log)
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3C286: 2499; OffOn 1/2
No active surface shielding
Samp 1,3/4, State 1-2/2, Ave of 6 Int.
Ascii Data (2003_05_01_23:06:53B.3.log)
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rfi-ac-on: 9; Track 1/1
Active surface shielding installed
Samp 1,2/2, State 1-2/2, Ave of 60 Int.
Ascii Data (2003_09_13_00:00:29A.4.log)
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rfi-ac-on: 10; Track 1/1
Active surface shielding installed
Samp 1,2/2, State 1-2/2, Ave of 60 Int.
Ascii Data (2003_09_13_00:02:30A.5.log)
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rfi-ac-on: 11; Track 1/1
Active surface shielding installed
Samp 1,2/2, State 1-2/2, Ave of 60 Int.
Ascii Data (2003_09_13_00:04:20A.6.log)
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rfi-ac-off: 15; Track 1/1
Active Surface power off.
Push to Off (1)
Ascii Data (2003_09_13_00:23:03A.2.log)
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rfi-ac-on: 10; Track 1/1
Active Surface power on.
Push to Off (1)
Ascii Data (2003_09_13_00:02:30A.3.log)
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rfi-ac-off: 15; Track 1/1
Spectra with Active Surface powered on -
spectra with Active Surface powered off. The intensity
scale is set to +/- 10K
Ascii Data (2003_09_13_00:23:03A.4.log)
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rfi-ac-off: 15; Track 1/1
Spectra with Active Surface powered on -
spectra with Active Surface powered off. The intensity
scale is set to +/- 1K
Ascii Data (2003_09_13_00:23:03A.5.log)
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These data were obtained by Jeff Acree, Wes Sizemore, Carla Beaudet,
Denise Wirt and Glen Langston.
The observing projects were 'TGBT01A061_02' and 'T_03MAY01'.
Object 'rfi-ac-on' was observed on 2003SEP13.
Data were written to directory: /home/gbtdata/TGBT01A061_02
Cable TV | Video Carrier | Audio Carrier |
Channel | (MHz) | (MHz) |
35 | 289.25 | 293.75 |
36 | 295.25 | 299.75 |
37 | 301.25 | 305.75 |
38 | 307.25 | 311.75 |
39 | 313.25 | 317.75 |
40 | 319.25 | 323.75 |
41 | 325.25 | 329.75 |
42 | 331.25 | 335.75 |
43 | 337.25 | 341.75 |
44 | 343.25 | 347.75 |
45 | 349.25 | 353.75 |
46 | 355.25 | 359.75 |
47 | 361.25 | 365.75 |
48 | 367.25 | 371.75 |
49 | 373.25 | 377.75 |
50 | 379.25 | 383.75 |
51 | 385.25 | 389.75 |
52 | 391.25 | 395.75 |
53 | 397.25 | 401.75 |
54 | 403.25 | 407.75 |
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Modified on
2003-Sep-16
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