Up date on my gr400f. i have not used my 4px for a year or two. When i tried to bind it with the gr400f receiver its a no go. But the receiver does bind with my futaba 3pk transmitter with fasst c1 module. I assume the receiver only operates in c1 fasst and not c2 fasst mode. the futaba 4px does work with my gr400s receivers ad the t-sfhss receivers i have just fine.