Summary

• All information will be moved from the main receiver page to this page soon.

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.

-- GalenWatts - 25 Sep 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

• KaMtgMay312007
• KaMtgJune82007
• KaMtgJune222007
• KaMtgJuly62007
• KaMtgJuly202007
• KaMtgAug32007
• KaMtgAug172007
• KaMtgAug312007 : Canceled
• KaMtgSept142007
• KaMtgSept282007 : Canceled
• KaMtgOct172007 : To decide near future Ka configuration.

Upcoming Meetings:

• November 30: Project Close Out Meeting, Agenda at KaMtgNov302007

Pictures

• Front.jpg: Inside view of dewar, modified version.
• Side.jpg: Side view of dewar internal components.
• 50Kabsorber.jpg: 50K radiation shield with absorber.
• KaFeedPatters.pdf: Feed patterns at 26, 32 and 40 GHz

Software Modification Requests

• Modification requests not completed by Sept 30 were suspended.

Lab Reports

• May, Dewar Symmetry, GBT Memo 248
• June, Basic Stability, GBT Memo 249
• August 15, Brief summary of results from modified Ka-band receiver tests
• Lab Spectrometer data from the tests of September 7-11 is in /home/labdata/TKA070907, .../TKA070909, .../TKA070910, .../TKA070910B, .../TKA070911. Each directory has a text file, 'Notes,' that explains the details of particular scans.
• 1vs2Deltas.pdf: Ratios in dB of OMT path measurements made with the lab VNA. 1 and 2 are Side/Thru of the corresponding OMT, 3-6 are ratios of paths of each OMT in combinations that could be implemented in the receiver in the dual beam/dual circular configuration. Plot 6 looks promising for Zpectrometry.

Lab Spectrometer Waterfall Baseline Plots from September, 2007

• Beam 2, 27.5/0.8 GHz:
  

• Beam 2, 33/0.8 GHz:
  

• Beam 2, 36.5/0.8 GHz:
  

• Beam 1, 39/0.8 GHz
  

Specifications for the Ka Receiver Manager fits file.

• KaRxFitsSpec

%META:TOPICINFO{author="GalenWatts" date="1190728007" format="1.0" version="1.1"}% %META:TOPICPARENT{name="KaBandReceiver"}%

GBT 26-40 GHz Receiver Modifications of Summer, 2007

• All information will be moved from the main receiver page to this page soon.

-- GalenWatts - 25 Sep 2007