I am trying to use the frequency offset mode of PNA-X to do the IMD measurement. But in generating the two tone signals, I noticed when I use more sweep points and narrower IF BW that each of the tone actually consists of two closely spaced tones (about 15MHz apart) of equal but -3 dB lower power than specified. In other words, I have now 4 tones. I tried different settings and found no clue. I am doing something wrong here. This is very strange. On the other hand, I happen t have the option 087 IMD application and tried that and found no such problem although it seems I cannot have as much control on the IF BW or resolution BW than I had with Frequency Offset Mode. I wonder if the additional tones are real.
The other issue I found is that I could not display the two tones (one from the PORT1 source1 and PORT1 source2) on one trace. For example, if I display R1 receiver response to check the incident signal, the menu requires me to specify the source as one of "NONE", "PORT1", "PORT2", "PORT3", "PORT4" and "PORT1src2". If I select PORT1, it will display the tone from PORT1 src1 but not from PORT1 src2. If I select PORT1 src2, it will display tone from PORT1 src2 but not from PORT1 src1. The Keysight application note however shows that I should be able to (I found my instrument menu different from that of the app note though, maybe due to firmware version, not sure).
Appreciate help on this,