Green Bank Telescope Spectra

Documentation



glangsto -at- nrao.edu

created on:

2003SEP15

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'.

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)
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)
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)
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)
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)
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)
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)
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)
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)
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)

Observing Setup

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 TVVideo CarrierAudio Carrier
Channel(MHz)(MHz)
35289.25293.75
36295.25299.75
37301.25305.75
38307.25311.75
39313.25317.75
40319.25323.75
41325.25329.75
42331.25335.75
43337.25341.75
44343.25347.75
45349.25353.75
46355.25359.75
47361.25365.75
48367.25371.75
49373.25377.75
50379.25383.75
51385.25389.75
52391.25395.75
53397.25401.75
54403.25407.75
Modified on 2003-Sep-16