"What's the good word, Harker? Picked up anything?"
Harker ran his fingers through his mop of black hair, and grimaced.
"Not a squeak, sir. No radio, no radar. Of course, the interference may be blanketing those. Creates a lot of false signals, too, on the radar screens. But we can't even pick 'em up with long-range sonar. That should get through. We're pretty sure they crashed, all right."
"How about our signals, Harker? Do you think we're getting through to them?"
Harker leaned back expansively, happy to expound his specialty.
"Well, we've been sending radio signals every hour on the hour, and radio voice messages every hour on the half hour. We're sending a continuous sonar beam for their direction-finder. That's about all we can do. As for their picking it up, assuming the rocket has crashed and been totally knocked out, they still have a radio in the whippet tank. It's a transreceiver. And they have a portable sonar set, one of those little twenty-pound armored detection units. They'll use it as a direction finder."
Chapman swirled the coffee around in the bottom of his cup and stared thoughtfully into it.
"If they can get sonar, why can't we send them messages down the sonar beam? You know, flick it on and off in Morse code?"
"It won't work with a small detector like they have, sir. With our big set here, we could send them a message, but that outfit they have might burn out. It has a limited sealed motor supply that must break down an initial current resistance on the grids before the rectifiers can convert it to audible sound. With the set operating continuously, power drainage is small, but begin changing your signal beam and the power has to break down the grid resistance several hundred times for every short signal sent. It would burn out their set in a matter of hours.
"It works like a slide trombone, sort of. Run your slide way out, and you get a slowly vibrating column of air, and that is heard as a low note, only on sonar it would be a short note. Run your slide way up, and the vibrations are progessively faster and higher in pitch. The sonar set, at peak, is vibrating so rapidly that it's almost static, and the power flow is actually continuous. But, starting and stopping the set continuously, the vibrators never have a chance to reach a normal peak, and the power flow is broken at each vibration in the receiver—and a few hours later your sonar receptor is a hunk of junk."