I didn't know what a Capsule Communicator was, I thought it was a piece of equipment used by astronauts in their space capsule. But it's a role if the ground crew; the person who is responsible for communicating with the astronauts.
Knowing that, the article makes more sense. Mission control has to send audio to transmit and also turn the transmitters on and off. They do that all in one data line (phone line) using these tones.
This sentence was real confusing. The transmitters were turned on and off by the people on Earth, but they were remote transmitters _on other parts of Earth_, not turned on and off remotely by the astronauts. The astronauts weren't turning Earth's transmitters on or off. Right?