Some observatories prefer the scale which differs from by the factor.
The conclusions of this paper mostly depend on ratios in which divides out, so the difference in definitions is not important. Real receivers, whether they are intended to be single or double sideband, have varying ratios of sideband gain , i.e. single sideband systems have imperfect rejection so that , while double sideband systems often have slightly unequal gain ratios so that . For quasi-optical systems the image termination temperature is also increased by optics losses, such as vacuum windows, grids, etc. Through arrangement of optics and by redirecting spillover between the ground and the sky, one can transfer losses between and . It is most advantageous to maximize since it contributes to both an ambient temperature noise term and a loss factor.