Hi every one.The spectrum analyzer in VNA is a nice function,but it still has some problem.It has a probability to record image signal.The patent said:With an unknown muilt-tone input RF spectrum,the chance of recording an image signal at any RF frequency for a multi-tone input RF spectrum of some arbitrary period is approximately (N*RBW/IFBW)^N.But I can't understand this equation and want to learn about how to calculate.Dose it mean that spectrum analyze result shown on the screen is not 100% truth?Thanks a lot.
Once again, the answer is complicated. I think you are referring to a publication that describes a kind of image reject method and aparatus. While it might be included in option 090 it is not the only methodology used. But, as with any non-real-time SA, there is a probability of intercept and if the the signal is not constant, then lots of factors will conspire to make the apparent spectrum not what would be measured on an RTSA. If the signal comes and goes, it may fool the image reject, so several things can be done in such a case: reduce the image reject strength from normal to miinium, change the detector from average power to peak voltage, and decrease the VBW. This will make the SA more sensitive to transient signals and more likely to pick up a signal that is coming and going. All SA's have this attribute, whether swept or stepped FFT. PNA-Based is similar to other FFT based SA and actually better than swept mode in the YIG bands.