G'day Ben,
Heatho and I, along with a few others were swinging pretty close with the SDC's at times. We must've been well under ten metres/thirty feet or so apart without major issues?
We did a little test with the Zed and SDC a couple of weeks ago, along with two Zed's. The Zed and SDC within ten to fifteen metres was no good. Just starts the threshold ambulance siren on the ZED, couldn't auto tune it out at that distance either. The SDC wasn't too bad, but got worse as it moved closer within that range.
The two Zed's seemed a little more co-operative and I could just hear the threshold breaking around ten metres. We were both on different channels.
The GPX's used to be a real pain at times when trying to work close. They didn't play very nice with other machines either.
Anything over ten metres with two SDC's you should be right out of the interference zone. The less interference the better when detecting :Y:
Cheers,
Shauno.