Tac's Page

　For the sideband-separting (2SB) mixer, the image rejection ratio (IRR), which is the value of rejecting power from the image sideband to the signal sideband in the heterodyne mixer receiver in SSB mode, depends on the quality of SIS chips and is changed by tuning the SIS bias voltage. Therefore, we have to check the IRR before each observation.

　We have developed a new measurement system for the IRR and installed this system on the 2SB receiver in the 45-m millimeter wave telescope at Nobeyama Radio Observatory (NRO) in Nagano, Japan.

　Using this measurement system, the applied bias voltage of the SIS chips can be tuned to the best performance of the IRR and we can improve the accuracy of the absolute intensity of molecular line. This is the first IRR measurement system developed for practical use.

　The IRR value measured by this system and that measured by the observations are consistent within an accuracy of ± 10 %. Therefore, we can obtain the best tuning of the 2SB mixer with the system to improve the accuracy of intensity calibration of molecular line observations.