Hello Chuckey,
here is my sample scenario. my channel is 5MHz operational BW. normally the specified measurement for shoulder distance (i think i was incorrect when i'm referring to as 3rd order, sorry for that) is 0.2MHz offset from the edges of the BW. Example my carrier is 2GHz centered in a 5MHz BW. I would like then to measure the distortion level at 2GHz-2.5MHz-0.2MHz at the low side and 2GHz+2.5MHz+0.2MHz for the high side. Since in MWO, they only have nth order IMD testings, I have to adjust my input tones such that their 3rd order IMD's are the low side and high side. my overall band inclusive of the side is 5+0.2+0.2=5.4MHz...divide it by 3 gives me 1.8MHz seperation...