1.3cm primary focus receiver (18-26 GHz)
This receiver was build for spectroscopic observations. It has a linearly polarized feed<. Plots of the calibration noise temperature vs. frequency are shown below, or can be found here: 1. broad band IF and 2. VLBA IF (the VLBA IF is used for the FFT spectrometer). Here you can find those values tabulated.

Frequency [GHz] Channel Polarisation Tcal [K] Tsys [K] Sensitivity [K/Jy] SEFD [Jy] Aperture Eff. [%] TMB/S [K/Jy] Main Beam Eff. [%] FWHM [arcsec] Last update
18.5 A+B linear 3.5 63 1.1 57 39 1.7 65 45.9 May 2009
19.0 A+B linear 3.3 60 1.06 52 37 1.6 65 45.5 Sep 2009
20.0 A+B linear 2.9 68 0.94 72 33 1.6 59 43.8 Feb 2008
22.0 A+B linear 2.2 63 0.9 69 32 1.5 61 42.7 Dec 2009
23.7 A+B linear 1.6 65 0.8 76 29 1.4 58 42.2 Jan 2008

normalized Gain curve     (G = A0 + A1·Elv + A2·Elv2) Observed in
A0 = 0.88196      A1 = 6.6278E-3      A2 = -9.2334E-5 Feb 2007

Comments:

  • Both, the horizontal and vertical linear polariztions are measured. Channel A contains the horizontal direction and channel B the vertical. Decoupling between both axes is larger than 32dB.
  • For continuum observations both channels were added to avoid artificial variations of linearly polarized sources caused by the linearly polarized channels of the receiver.
  • Note that the system temperature at this frequency strongly depends on weather conditions!
  • Spectroscopic observations of sources with significant continuum emission at frequencies >23 GHz might suffer from instable baselines. This could cause problems when measuring weak, broad lines. Possible solution: the new control system allows to drive the focus on a cosine wave with a given amplitude (e.g. lambda/8) and frequency during the measurements. This largely suppresses the appearance of standing waves and therewith improves the baseline stability.


Fig. 1 (top): Tcal against frequency for the VLBA IF estimated from hot-cold measurements.
Fig. 2 (bottom): Tcal against frequency for the brad band (BB) IF estimated from hot-cold measurements.