"Nothing but."
The cabinet provided a standard potentiometer, and as Don advanced the amount of fed-back voltage, Freddie's voice came booming in louder and louder. It overloaded the audio amplifier, and they turned the gain down as Channing increased the in-phase voltage more and more. It passed through a peak, and then Don left the potentiometer set for maximum.
"Wes," he said, "call Freddie and tell him to take off for Terra, at about four G. Have the gang upstairs hang a ship beam on him so we can follow him with suggestions. Too bad we can't get there immediately."
"What I'm worrying about is the available gain," said Wes. "That thing may have given us a gain of a couple of thousand, but that isn't going to be enough. Not for planet-to-planet service."
"Later on we may be able to hang a couple of those things in cascade," suggested Walt.
"Or if not, I know a trick that will work—one that will enable us to get a gain of several million."
"Yeah? Mirrors, or adding machines? You can't make an audio amplifier of a three million gain."
"I know it—at least not a practical one. But, we can probably use our audio modulator to modulate a radio frequency, and then modulate the driver with the RF. Then we hang a receiver onto the detector gadget here, and collect RF, modulated, just like a standard radio transmission, and amplify it at RF, convert it to IF, and detect it to AF. Catch?"
"Sure. And that gives me another thought. It might just be possible, if your idea is possible, that we can insert several frequencies of RF into the tube and hang a number of receivers on the detector, here."
Arden laughed. "From crystal detection to multiplex transmission in ten easy lessons!"