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GBT 26-40 GHz Receiver Modifications of Summer, 2007

Summary

In January, 2007 initial testing with the Zpectrometer was completed and the Zpectrometer was removed from the telescope. A suspected gain offset somewhere in the cooled section of the receiver greatly limits the capabilities of the Zpectrometer; the receiver remained on the telescope exhibiting excellent performance with the Caltech Continuum back end. Continuum observations were performed through the end of April, 2007.

In early Summer 2007 it was decided to temporarily reconfigure the receiver to improve the symmetry of the circuitry before the first hybrid in an effort to reduce a gain offset in that circuitry indicated by lab testing during Spring, 2007. This reconfiguration will result in a receiver of two beams with the previous 1.35 arc minute separation, each beam providing one linear polarization perpendicular to the other beam. This configuration results in a simpler, more symmetric circuit before the first hybrid with fewer components and therefore less loss before the cryogenic amplifier stages. Drawbacks are the loss of circular polarization capability and the loss of half the receiver channels requiring longer integration times for all observers. It is hoped that improvement in receiver temperature from less loss in the dewar circuitry will offset some of the necessary increase in integration time. Permanence of this change will be decided after review of lab and on-telescope results during Fall and Winter, 2007.

Components removed from the dewar circuitry before the first hybrid are the circular to square transitions, the ridged wall polarizers, the square waveguide 45 degree twists, the ortho-mode junctions and some sections of rectangular WR28 waveguide. In their place will be circular to WR28 transitions, WR28 45 degree twists and a pair of custom fabricated WR28 E-plane 90 degree bends. All other receiver components and specification including feed separation and location will remain unchanged.

Recent meeting minutes

Upcoming Meetings:

Pictures

Software Modification Requests

Lab Reports

Lab Spectrometer Waterfall Baseline Plots from September, 2007

Each trace is (Scan B - Scan A)/Scan A, earlier scan are towards the bottom.

Specifications for the Ka Receiver Manager fits file.

Attachment: sort Action: Size: Date: Who: Comment:
Front.jpg action 592313 27 Nov 2007 - 19:35 GalenWatts  
Side.jpg action 201037 27 Nov 2007 - 19:35 GalenWatts  
50Kabsorber.jpg action 214220 27 Nov 2007 - 19:35 GalenWatts  
KaFeedPatters.pdf action 296959 27 Nov 2007 - 19:35 GalenWatts  
1vs2Deltas.pdf action 564727 27 Nov 2007 - 19:37 GalenWatts  
B1G39.png action 113268 27 Nov 2007 - 19:41 GalenWatts  
B2G33.png action 111967 27 Nov 2007 - 19:42 GalenWatts  
B2G275.png action 115530 27 Nov 2007 - 19:42 GalenWatts  
B2G365.png action 114241 27 Nov 2007 - 19:42 GalenWatts  

Topic KaMods2007 . { Edit | Attach | Ref-By | Printable | Diffs | r1.2 | > | r1.1 | More }
Revision r1.2 - 27 Nov 2007 - 19:56 GMT - GalenWatts
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