Y2,

The answer is if both units are set to same frequency, ie 50Khz or 200Khz you will have issues. You need, if possible select 50khz on one and 200khz on the other. This works in my boat fine. Remember the higher the frequency the more detail but less depth, which unless your going off shore is irrelevant. You can determine which is best for your tastes, but not all units offer this selectability make sure you buy  a second unit that does. I believe your 520 does.

Steve

If your transducerss are on the outside of your boat. Tilt the transducers away from each other. It does not have to tilt that much, just enough so the cones don't cross.

Daryl

From what I have seen...the cones will overlap even in shallow water...as for the shutting off thing....you might need some kind of RF protector in your wiring to the sonar unit...I believe the starter creates so much interference or power surge, it scrams the unit....not sure though.

i think you get the interference when your fishing deep water and both cones overlap. or does it happen all the time? as far as the console unit turning off mine does that too and i dont know why.

troy

Do you guys run both sonars at the same time? When I do, I have interference on my LMS520C at the console. Is that normal? My bow fishfinder is a X65, soon to be replaced by an X97. Another question is when I start up the main motor my console unit turns itself off, so I have to turn it back on everytime I move to another fishing spot.