Thank you W5DXP, all inputs really helpful!
You are right in that we are working in the dark until we can source some technical info. You have answered my question though - it's not gridlines.... Also, I wouldn't expect the results of aliasing (lack of lo pass filter) to be causing regularly spaced spot frequencies (plus they don't even look modulated?). It more has the look of some kind of beat between two frequencies closely related and I cannot even guess what's happening there. The I and Q signals arise from quadrature modulation but that comes from two identical frequencies locked together via 90 degree phase shift so not that!
Do we have anyone in the Group that has a contact in Xiegu? I heard (Bob Nagy?) that the spec to for wasthe IQ output was be released around the time that the add-on 5" display was announced but I've seen no marketing info on a date for that.
I've only had my G90 for three weeks but I've been on hold in the Scottish Highlands for the last two - so really looking forward to the 're-union' tonight (ha!). I've built an endfed antenna as my first experience and now looking to build a doublet using kit from DC Commander.