These are very long radio waves which require a specially built receiver.
These are subscription services requiring a special receiver.
Hence most stories assume that teleportation requires both a transmitter and a receiver.
It requires a light touch on the ball - and a big receiver.
In simple - terms, communication requires a sender, a receiver, and a communication channel.
Distance telepathy is a specialized thing, and it generally requires both a sender and a receiver.
The machines themselves were expensive (£22 15s 0d in 1928) and required a good receiver to operate.
On the other hand, a large great room in a suburban house requires a receiver that can pump out sound at a higher level.
Since their density is high they require a smaller receiver.
A working system requires both a ground transmitter and a receiver in the airplane.
