Figure 1: Receiver temperatures (SSB) of the new receivers, measured in the standard reference plane, and compared with those of the ``old'' receivers. See text for important details.
Figure 1 shows the receiver temperature of the new receivers, (the official names of the new receivers are A100 and A230), compared with the previously operating receivers in the same frequency bands. The values for the new receivers were collected during the installation and commissioning period, using the system cold load in the standard reference plane. The tunings were always made for both receivers simultaneously for an arbitrary pair of frequencies, and therefore include the compromise and associated loss in the MP diplexer setting. Three values for A230 were edited out, two because they were obtained at the beginning of the test period when the MP encoder origin was off by 35 m, and one because it was obtained with the 1M filterbank, which has an offset. The tunings were all done automatically under computer control, using the tables prepared in Grenoble, with no further optimization.
The values for the ``old'' receivers come from calibrations with continuum detectors over the period Jan-May 1998, and were compiled by J.L.Santaren. These values also include diplexing losses.
To summarize, expect typically 70K SSB across the band of the A100 receiver (possibly 10K more if the combination with the A230 frequency is ``unlucky'', possibly less if measured narrow-band with the autocorrelator backend), and for the A230 receiver, 110K up to 225 GHz, 140K at 230 GHz, 170K at 240 GHz, again give or take 10K depending on the associated frequency for the A100 receiver and on the backend used for the calibration.
We intend to improve the noise performance in the 230 band using smaller area junctions.
The values in the standard reference plane suffer the impact of the optical losses, and do not do full justice to the performance achieved in the laboratory expressed at the dewar window. However, in the context of the Newsletter, they are the index of performance of interest to the end users. The dewar-window values and the breakdown of optical losses will be analyzed in a forthcoming technical report.