Heart in the mouth time at the weekend as I experienced by first signal loss with RTH automatically activated. Fortunately the aircraft was really close to me so no great panic but I launched from a fairly thin piece of pathway by a river so was concerned about the accuracy of the RTH landing him in the water. He returned as expected and I (for some reason) couldn't cancel the RTH so I reverted to ATTI mode and took control as I didn't want him to land. All in all no big deal but was momentarily worrying. The Phantom was only 550ish feet away when it happened so can only assume the train line bridge I flew over interrupted the signal?