My first radio system was a used Controlaire six channel reeds system, which was really only three functions. This system was out of date when I got into RC in the 1970's. The receiver contained a "reed bank" that consisted of metal strips that would vibrate a certain tone and the corresponding servo would move. Receiver had to be placed in the plane a certain direction for the receiver to operate.
The radio worked pretty well until one day it quit working right after take off in a Midwest Esquire. When the tank ran out, the plane was so high you could not see it. A farmer found the plane several miles away a couple of weeks later. His cows had done some damage to the wings but I repaired the plane and put in proportional radio equipment.
Reed equipment was not proportional, moving the spring-loaded toggle switch on transmitter started servo moving in one direction until the switch was returned to neutral, then the servo returned to neutral. Throttle servo did not return to neutral but stayed at the position it was at when the toggle switch was returned to neutral. Only one function could be performed at a time. There was no trim or servo reversing.
I later sold the plane for someone to learn on. Another guy sold him a radio and helped him fly the plane. When the owner of the plane got in trouble, he handed the transmitter to the instructor and the plane crashed. The instructor looked at the transmitter and the power switch was off. He asked the student why he shut the switch off and he said, "when you are operating power equipment and there is trouble, the first thing you do is shut the power off." Not a good idea with RC equipment.