Verified Spurious Equations September 30

Verification of spurious in the (T_KFPA_30SEPT08)plots:

  • (-1 LO1 + 2 LO2 - LO3 + LO4) DONE spectrometer scans.
    • Scan 8 LO1 = 15.85 LO2 = 8.90 LO3 = 11.4 LO4 = 10.5 gives a spur @ 1.95 GHz in the IDM IF band: 30SEP_scan8.ps
    • Scan 50 LO1 = 15.85 LO2 = 8.90 LO3 = 11.4 LO4 = 10.5 with HPF filter added after doubler 30SEP_scan50.ps

  • (4 LO1 - 7 LO2 - LO3 + LO4) DONE spectrometer scans.
    • Scan 55 LO1 = 15.85 LO2 = 8.90 LO3 = 11.4 LO4 = 10.5 with HPF filter added after doubler: 30SEP_scan55.ps

  • 4 LO1A - 6 LO2 - LO3 + LO4 DONE spectrometer scans.
    • Scan 8 LO1 = 13.85 LO2 = 8.90 LO3 = 11.4 LO4 = 10.5 gives a spur @ 2.0 GHz in the IDM IF band:30SEP_scan22.ps

Spurious Equations September 18

The spurious in the (T_KFPA_08SEPT18)plots can be explain by the following equations where:
  • GBT LO1A = LO1 (this frequency is doubled)
  • GBT LO1B = LO2
  • GBT LO2 = LO3
  • GBT LO3 (fixed 10.5 GHz) = LO4

  • 2 LO1A - 3 LO2 - LO3 + LO4 DONE Known Large Spur.
    • Scan 4: LO1 = 14.45 LO2 = 8.9 LO3 = 11.4 LO4 = 10.5 gives a spur @ 2.2 GHz in the IDM IF band.
    • The spectrometer with sampling frequency 1.6 GHz spectrum: KFPA_Scan4.ps

  • (-LO1 + 2 LO2 - LO3 + LO4) DONE spectrometer scans.
    • Scan 20: LO1 = 15.95 LO2 = 8.9 LO3 = 11.4 LO4 = 10.5 gives a spur @ 1.85 GHz in the IDM IF band.
    • The spectrometer with sampling frequency 1.6 GHz spectrum: KFPA1LO1A.ps

  • (-6 LO1 + 11 LO2 - LO3 + LO4) DONE spectrometer scans.
    • (Appears with LO1 greater than 15.75 GHz)
    • Scan 22: LO1 = 15.95 LO2 = 8.903 LO3 = 11.4 LO4 = 10.5 gives a spur @ 2.233 GHz in the IDM IF band.
    • The spectrometer with sampling frequency 1.6 GHz spectrum: KFPAScan22.ps

Additional spurious found in T_KFPA_08SEP11 OrionA scans:

Spurious Equations September 18

The spurious in the (T_KFPA_08SEPT18)plots can be explain by the following equations where:
  • GBT LO1A = LO1 (this frequency is doubled)
  • GBT LO1B = LO2
  • GBT LO2 = LO3
  • GBT LO3 (fixed 10.5 GHz) = LO4

  • 2 LO1A - 3 LO2 - LO3 + LO4
    • Scan 4: LO1 = 14.45 LO2 = 8.9 LO3 = 11.4 LO4 = 10.5 gives a spur @ 2.2 GHz in the IDM IF band.
    • The spectrometer with sampling frequency 1.6 GHz spectrum: KFPA_Scan4.ps

  • (-LO1 + 2 LO2 - LO3 + LO4)
    • Scan 20: LO1 = 15.95 LO2 = 8.9 LO3 = 11.4 LO4 = 10.5 gives a spur @ 1.85 GHz in the IDM IF band.
    • The spectrometer with sampling frequency 1.6 GHz spectrum: KFPA1LO1A.ps

  • (-6 LO1 + 11 LO2 - LO3 + LO4) (Appears with LO1 greater than 15.75 GHz)
    • Scan 22: LO1 = 15.95 LO2 = 8.903 LO3 = 11.4 LO4 = 10.5 gives a spur @ 2.233 GHz in the IDM IF band.
    • The spectrometer with sampling frequency 1.6 GHz spectrum: KFPAScan22.ps

Additional spurious found in T_KFPA_08SEP11 OrionA scans:

  • -4 LO1A + 6 LO2 - 2 LO3 + 2 LO4 DONE verified with spectrum analyzer. ~ -117 dBm
    • Scan 100: LO1 = 12.65 LO2 = 8.9 LO3 = 11.4 LO4 = 10.5 gives a spur @ 2.8 GHz in the IDM IF band.
    • Scan 102: LO1 = 12.85 LO2 = 8.9 LO3 = 11.4 LO4 = 10.5 gives a spur @ 2.0 GHz in the IDM IF band.

  • (-6LO1 + 7 LO2 - LO3 + LO4) ALERT! unable to locate with Lab spectrometer.
    • Scan 112: LO1 = 13.85 LO2 = 8.9 LO3 = 11.4 LO4 = 10.5 gives a spur @ 20.8 GHz in the IDM IF band.

  • (-2 LO1 + 1 LO2 + 2 LO3 + LO4) ALERT! unable to locate with Lab spectrometer.
    • Scan 124: LO1 = 15.25 LO2 = 8.90 LO3 = 11.4 LO4 = 10.5 gives a spur @ 21.6 GHz in the IDM IF band.

  • (-1 LO1 - 3 LO2 + 1 LO3 - 2 LO4) ALERT! unable to locate with Lab spectrometer.
    • Scan 128:134 LO1 = 15.65:16.25 LO2 = 8.90 LO3 = 11.4 LO4 = 10.5 gives a spur @ 11.05:10.45 GHz in the IDM IF band.

IF Spur Investigations

On September 18, 2008, Steve W. and Glen L. investigated the GBT Single pixel receiver IF spurs by setting different combinations of LOs and watching the IF spurs move. Below are four tests, where the LO frequencies are modified slightly. The K band single pixel tests used 4 LOs to bring the astronomical signal into the Spectrometer input band of 800 to 1600 MHz. We performed three sets of tests with sky frequencies centered on 22.1, 22.32 and 25.1 GHz. The fourth LO is in the converter rack and is fixed at 10.5 GHz.

The data are associated with GBT project T_KFPA_08SEP18

The telescope was at access during the observations. The sky frequency on the plot is correct only if LO2=8900 MHz, LO3 = 11400 MHz and LO4 = 10500 MHz (fixed).

Scan LO1 LO2 LO3 color
Number(MHz)(MHz)(MHz)
4 14450890011400white
5 14475890011400
6 14433890011400
7 14450891011400red
8 14450891011410
9 14450890011410blue
10 14451890011400green
11 14451891011390orange

Equation for offset: 1.6-(2 LO1A - 3 LO2 - LO3 + LO4)

Note: As a consequence of 100 MHz LO sidebands, the spurious occur in triplets.

ifSpur04-11.gif
Scan LO1 LO2 LO3 Color
Number(MHz)(MHz)(MHz)
12 14560890011400white
13 14563890011400red
14 14565890011400blue
15 14560890711400green
16 14560890311400
17 14560890011410orange

ifSpur12-17.gif

Scan LO1 LO2 LO3 Color
Number(MHz)(MHz)(MHz)
18 14560890011480white
19 14560890211480red

Equation for offset: 1.6 -(2 LO1 - 3 LO2 - LO3 + LO4);

ifSpur18-19.gif

Scan LO1 LO2 LO3 Color
Number(MHz)(MHz)(MHz)
20 15950890011400white
21 15953890011400red
22 15950890311400blue
23 15950890011403green
24 15935890011400orange
ifSpur20-24.gif

Equation for offset: 1.6-(-LO1 + 2 LO2 - LO3 + LO4) Note: Triplet not evident in these plots.

-- GlenLangston - 18 Sep 2008

*

* : 30SEP_scan8.ps

* 30SEP_scan50.ps: 30SEP_scan50.ps

* : 30SEP_scan55.ps
Topic attachments
I Attachment Action Size Date Who Comment
30SEP_scan22.psps 30SEP_scan22.ps manage 26 K 2008-09-30 - 14:42 StevenWhite  
30SEP_scan50.psps 30SEP_scan50.ps manage 14 K 2008-09-30 - 14:32 StevenWhite  
30SEP_scan55.psps 30SEP_scan55.ps manage 15 K 2008-09-30 - 14:38 StevenWhite  
30SEP_scan8.psps 30SEP_scan8.ps manage 12 K 2008-09-30 - 14:32 StevenWhite  
KFPA1LO1A.psps KFPA1LO1A.ps manage 63 K 2008-09-25 - 09:14 StevenWhite  
KFPAScan22.psps KFPAScan22.ps manage 13 K 2008-09-25 - 09:16 StevenWhite  
KFPA_Scan4.psps KFPA_Scan4.ps manage 70 K 2008-09-24 - 15:30 StevenWhite  
ifSpur04-11.gifgif ifSpur04-11.gif manage 16 K 2008-09-18 - 16:16 GlenLangston  
ifSpur12-17.gifgif ifSpur12-17.gif manage 18 K 2008-09-18 - 16:16 GlenLangston  
ifSpur18-19.gifgif ifSpur18-19.gif manage 12 K 2008-09-18 - 16:16 GlenLangston  
ifSpur20-24.gifgif ifSpur20-24.gif manage 13 K 2008-09-18 - 16:17 GlenLangston  
Topic revision: r57 - 2008-09-30, StevenWhite
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding NRAO Public Wiki? Send feedback