The sensor module used with 8163B is 81636B, and the device is driven by a software called IL Engine. After a ZERO was performed to the input channel, the noise displayed on the screen of 8163B started to become very unstable, ranging from -60dbm to -80dbm. And setting a calibration has a little because when a 'run' order is performed by the software to plot the measurement，the calibration and the averaging time set before will be reset to 0dBm and 25us, respectively. Has someone met the same problem before and could anyone provide some suggsetions to address the problem so that the noise could be stabilized near a specific value. (hope I have described the problem clearly)
Any advice would be of great help.