A new dual-frequency receiver has been installed on antenna 4 at the end of August. It covers the 80--115 GHz and 210--250 GHz bands, and both mixers can be used simultaneously. The 3mm mixer allows true LSB tuning at all frequencies with high image sideband rejection, and good USB tuning (although with low rejection) at 115 GHz. Measured system temperatures are indicated below:
These measurements were obtained in rather poor weather conditions. Column 5 indicates typical measured with the other antennas at the same time. Sensitivity has been improved by a factor 2 above 110 GHz. However, as expected, pure DSB tuning is not only less sensitive, but also very difficult to achieve above about 100 GHz. Observers are requested to consider seriously this problem in their applications.
Because of poor weather conditions, only a crude check of the pointing of the 230 GHz receiver has been made so far.
Unfortunately, problems with cryogenics have delayed the other 3 receivers, and no fixed schedule can be given yet.