I have an analog receiver (TechniSat ST 3002 S) and a Philips CRT TV on my setup and you can see black screens on the strong carriers which have these ring shaped IQ constellations.
I observed different testing modes for the transponders on 1P being tested:
1. full bandwidth mode - lower power -> no "ring", no "black screen"
2. full bandwidth mode with narrow high power carrier at the transponder's centre frequency ->ring and black screen
3. full bandwidth mode with narrow high power carrier at the lower margin of the transponder (around -12 Mhz from centre frequency with a "tusk"-shaped spectrum on Crazyscan) ->ring and black screen
4. the same as 2. but without full bandwidth "basement" carrier
It is interesting to note that in some tests there are lower power peaks at the opposite polarization which seem to be switched on and off. I have a mechanical polarization skew motor on my setup which is optimized at 9.5 deg West.
