AbcdforAstronomers

ABCD dual polarisation receivers (till mid March 2009)

• Eight single pixel receivers A,B,C,D are installed in the receiver cabin. It is planned to replace them by EMIR in mid March 2009.

• Four of the 8 A,B,C,D receivers can be used simultaneously. HERA cannot be combined with other receivers.

Remarks:

1. Using a special external LO, frequencies down to 77 GHz can be measured with good sideband rejection. For frequencies below 77 GHz, the sideband recection becomes weaker, and the sideband ratio reaches unity at 72 GHz. Test report of 2004, Test spectra

2. Noise increasing with frequency
3. Last status before dismantling the ABCD receivers in March 2009:
   • Image/Signal gain-ratio calibration using the continuum backends(!) is supported by NCS, processing in MIRA. It is highly recommended to use this feature!
   • Cold load temperature:

     • A standard table of Tcold calibration temperatures for A, B, C, D receivers is implemented in the NCS. This built-in table covers most frequencies. (Use: pako>receiver /temp L)

     • Outside this range, Tcold has to be set manually (use pako>receiver /temp "Tcold"), ask the RX engineers or operators! Tables and plots (internal link) (2007-10-11 dj)

   • CHECK Receiver C150 shows low continuum signal at the higher frequencies (>168 GHz). It has to be fully checked. Use D150 instead. (2005-11-16)

   • In the receiver cabin, Martin-Puplett interferometers MPI are used to seperate frequencies to be send to two different receivers. An overview of the receiver cabin optics is given here. The MPIs have high losses at certain frequency ratios, especially at a ratio of 3. Simultaneous observations of e.g. HCN(1-0) and HCN(3-2) or HCO+ are therefore difficult and may lead to increased receiver noise temperatures, depending on how the MPI is optimized.