SR300 - nope, it won't work - that uses the original DSM protocol (and caught me off guard a few months ago when I got my (newer non-DSM compatible) DX4S radio - I thought it was a DSM2 rx untill I pulled up the data on Spektrum's web site).

SR3520 - non-issue - that's a DSM2 protocol rx (I know, you didn't ask about that one - but since it's older like the SR300, I figured that I might as well list it).

SR310 - non-issue, it's a DSMR protocol rx.

Hope that help clears up the confusion.