The “testing” in the car that I did was using the radar screen only to see what it did when moving etc.
What I shall do here is drive to the top of a local hill, elev 1500 ft in clear line of sight with Edinburgh, Perth, Glasgow and sit still in peace.
It may be that Perth circuit traffic was mostly training aircraft, perhaps on mode c/s.
I shall try to get some sort of positive result one way or the other rather than one isolated flight, whilst flying the thing in a busy circuit.
Just surprised that the very clear bright green UFO looking things that Runway hd should display were not there although should be difficult to miss.
I have seen occasional traffic on good days with the unit on the window sill facing south and surrounded by trees. So the display is, or seems to be working correctly.