Above 114 GHz, only the USB tuning works. Below 114 GHz, if only one line has to be observed, use the LSB setting. Receivers can be tuned with sideband rejection, thus improving significantly the system temperature (up to a factor 2).
When one line must be observed in each band, the Doppler tracking is exact only for one of the two receiver bands. Presently, no software correction is implemented to correct for the resulting frequency shift. Since the elapsed time for any observing project will be typically 2 months, the observer should take care of this peculiarity if the desired spectral resolution is higher than 0.3125 MHz (in practice, this happens for the 20 and 40 MHz band with 256 channels). Otherwise, the effect can be neglected. Source to source variations may be important. éIn such a case, select the band according to the line to be observed with the highest resolution, or according to the most important line if resolutions are identical.