Odd traffic Warning

[GrahamB]

On a few occasions we have had a "Mode C" warning circle show on Sky Demon with a strange designation C-? where the ? are seemingly random characters (but could be Hex codes), we also get a black and yellow warning box on the SD screen that warns of an aircraft at 12 o'clock. In all cases nothing is actually there or at least seen.

I guess this is a warning that is coming from something other than a standard PAW contact. I suspect that others will know what we are seeing and we would be grateful if someone could advise.

[Ian Melville]

I've been seeing this for a long time and seems to also apply to Mode S traffic that that has no ES(you see the reg rather than C-?). Also Full mode S with ES that is on the ground. Lee seems to think it is an SD issue, but I am not so sure as PAW gives a corresponding Audio alert. I don't know if it is the same for you, but it seems to only happen when I am moving, either by road or air, which make it very difficult to reproduce.