Changes to Zpectrometer setup


2008 Mar 7: Installed broadband filter and adjusted padding for total power gain  monitor.  See session 40.  Power supply monitor point logging now running.


2008 Aug 25-29: Changed backplanes on all correlators to eliminate plug-socket Phoenix connector. 
                            Added band-limiting filters to Port A inputs on BE to try to recover spectrum across lower 2 GHz of band (cwcal dies off earlier than Rx noise?)
                            Replaced fiber interface and hub with integrated unit.
                
2008 Oct 30: Install Zpectrometer on GBT. 
2008 Nov 3: Finished installation.  Complete total power chain, changed high-lag amp module on BE3 (turned out to be a bad pad at input)

2008 Dec 16: Migrate software to RH Enterprise 5 software announcement.

2009 Jan 6: Galen moved BE0 filters from Port A to Port B, tightened connectors in receiver.  Zero lag now inside correlator.
2009 Jan 7:  Sess. 23 follows for test.  First remarks about pointing difficulties, but weather is very bad.  Passband gain 1.6 lower than previous.
2009 Jan 8: Galen looked at IF outputs from cryostat etc.  email "Ka Receiver Ripple, Jan 8." 

2009 Jan 12: Rx off telescope to look for ripple, change cold head components
2009 Jan 13: Lab work, warm Rx.  Added isolators at outside of cryostat wall, swapped tripler/LO splitter units between arms.  Rebiased to minimize second harmonic. 
                     Unexplained step changes in power output at J4, about 4 dB.
2009 Jan 16: Back on telescope, first tests Jan 16 (session 24).  Set attens 2,2,2,2 dB (sess. 24).  Still ripples.  See sess. 26 scan 40 for large example

2009 Jan 23: Galen redoes insulation arount total power circuit, offset back to normal at -0.216 V.  But total power is now about 0.5 V on sky after receiver work. 
                     Total power values were bad from 09:15 on Jan 6 (filter change?) to 14:45 on Jan 23, so sessions 23-26 are affected.

2009 Jan 24: Check levels and set attens at 0,0,0,0 dB (sess. 27).  No idea why power has dropped. 
                     Pointing had been difficult to impossible in sess 23-27 plus Smail/Hainline obs, S/N looked lower than usual; related?
                     Pointing S/N seems to improve after restarting LO1 system (to solve LO1B off, which killed pointing) in sess. 32,  1/31/2009

2009 Jan 29: Changed band edges in redBodyC.scr to [55, 492, 55, 492, 55, 492, 55, 57] from [50, 490, 50, 490, 50, 490, 50, 270], trim off BE0

2009 Feb 11: Laura Hainline adds Fourier-component ripple removal, released as redBodyD.scr.

2009 Feb 26: Galen swaps total power monitor from IF downconverter box Mon A to Mon B.  Tapped on various parts of the receiver and Zpectrometer, saw no power variations larger than 0.1 dB.  Total power and gain values should be different now.

2009 Mar 02: Measured receiver gain at downconverter monitor port B with noise diode/demodulator setup: 7 to 9 dB gain difference compared with port A, hard to pin down exact value since gain changes with time (see plot).  Total power tracks shapes, with additional noise.  Power drift seems to be "reset" with relay throw -- sign of a bad relay?  Correlator variances higher, set attens to 1,1,1,1 dB.   cwsigs comparison shows +2.4 dB gain change since last cwsigs on 2009 Feb 15.  8C-9 and 9A-64 had one run each here between swapping total power monitor point and the 8C-9 session that provided these data.

2009 Mar 06: Galen replaces relay after downconverter -- contact came unscrewed from relay instead of cable. Total power monitor still on downconverter port B.   Ray is tracking down a problem that results in scans being logged but not written as files -- something stops the data acquisition program.

2009 Mar 10: Galen moves total power detector back to downconverter monitor port A.  Spectrometer testing with warm load over both horns shows 300 MHz ripple.

2009 Mar 20: Galen replaces pad and cable between PIN switch and downconversion mixer.  This area was sensitive to cold and mechancial stress, and one cable end appeared to have a crack at the connector interface.

2009 Mar 30: Galen replaces oscillating bias cards.  Had previously added thermal blanket around cryostat to reduce cavity mode changes with temperature.  Tests with 9A40 at night showed ripples with varying periods; see "Last night's Ka tests" email 3/31/09.

2009 Mar 31: Decision made to remove Rx on Thu, 4/2, return to telescope in early May for other projects, back down at the beginning of June for the summer.

2009 Apr 2: Receiver removed, Zpectrometer powered down.

2009 May 30: Receiver reinstalled with heavy thermal insulation.   Area near downconverter mixers was very temperature sensitive; downconverter mixers have different thermal sinking than before.  Zpectrometer powered up.  The plan was also to replace the LNA bias cards with a previous generation, as the version that has been in use is prone to oscillations (see Mar 30, initial NRAO wiki notes on Rx).  

2009 May 2-6: First tests in poor weather; looks like zero lag has moved out of correlator.  This is later (May 6) traced to phase flips in the cwsigs data, origin unclear.  On May 5 Galen removes a 3 dB pad to shift lag pattern (which turns out not to be the problem) and to increase power level.

2009 May 10: Observations in moderate weather show many spectra with baseline ripples.  







Questions or comments?  Please contact Andrew Harris.