I am seeing some strange artifacts when I run a spectrum scan on 160M. I see this on both the input and output of the filter. The scope trace shows a perfect sine wave so I suspect that this is some sort of error on my part in setting up the scan. The input run is around -10dbm directly tee’d off the input to the amp. The output is from a tap on the output of an amplifier that is putting 50W into a dummy load.
The 80M scan is what shows as a more normal run. (I don’t know how to remove the spikes at 12 and 31. Those show up on all of my LPF runs, not just 80M.
I am guessing that I don’t have the ref set properly? I am at 0db.
I’ve run a quick test using an RSP1A and get results similar to those you have posted. Reducing the signal input level to the RSP caused the spur levels to reduce. At an input level of around -20 to -25dBm the spurs had gone. If you still have problems, please post a full screen-shot of the analyser as this lets me see any other settings that could be causing problems. A reference level of 0dBm is OK – Check front of manual for information about gains and what the reference level setting is actually doing.