Verified Spurious Equations September 30

Verification of spurious in the (T_KFPA_30SEPT08)plots:

• (-1 LO1 + 2 LO2 - LO3 + LO4) 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) 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 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 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) 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) 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 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) 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) 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) 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 14450 8900 11400 white 5 14475 8900 11400 6 14433 8900 11400 7 14450 8910 11400 red 8 14450 8910 11410 9 14450 8900 11410 blue 10 14451 8900 11400 green 11 14451 8910 11390 orange 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.
Scan LO1 LO2 LO3 Color Number (MHz) (MHz) (MHz) 12 14560 8900 11400 white 13 14563 8900 11400 red 14 14565 8900 11400 blue 15 14560 8907 11400 green 16 14560 8903 11400 17 14560 8900 11410 orange
Scan LO1 LO2 LO3 Color Number (MHz) (MHz) (MHz) 18 14560 8900 11480 white 19 14560 8902 11480 red Equation for offset: 1.6 -(2 LO1 - 3 LO2 - LO3 + LO4);
Scan LO1 LO2 LO3 Color Number (MHz) (MHz) (MHz) 20 15950 8900 11400 white 21 15953 8900 11400 red 22 15950 8903 11400 blue 23 15950 8900 11403 green 24 15935 8900 11400 orange

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