SparkFun RTK Express Surveying KitWe generally recommend using your cellular phone as the radio backhaul for RTCM but you can also use your own, higher power radios as long as they support 57600bps. We also recommend logging all data to your phone over Bluetooth. This is as simple as checking a box within SW Maps. But if you prefer to do long surveys, or need to deal with RAWX measurements where a phone will not be present, a microSD card should be purchased (any size up to 32GB).