Unless my memory failed me I remember that a Spektrum SM3001 was a transmitter module. All Spektrum Surface Receivers are designated SR, get it, SURFACE RECEIVER = SR.

SM meant Surface Module.

There is only one SR3100 and that's their DSM2 Receiver also in DSM2 is their SR3520.

Here's their line up of car/truck receivers: http://www.spektrumrc.com/DSM/Produc...Receivers.aspx

Maybe you are confusing it with their Marine receivers but those are designated as MR for, you guessed it, MARINE Receiver.