"We're doing a lot of hoping, anyway," said Bob. "Are they keeping you pretty busy these days?"
"I should say so," said the radio inspector. "There's one fellow in particular that I'm having a lot of trouble with. I've got his location approximately, but in the neighborhood where he should be I haven't been able to locate any antennae to indicate the presence of a radio station. Usually it's easy enough, but this fellow seems to be a sly fox."
"How in the world do you locate an unauthorized station, anyway?" queried Bob.
"In each district in which there is a radio inspector we have what we call directional finders. These consist of a combination of a loop aerial and a compass and a radio receiving set. We have complete maps of the district. When the man we're after is sending, we swing the loop aerial around until the signals reach their loudest tone. Then a reading is taken on the compass. This action is repeated several times, after which we turn the loop so as to tune out all sound. During the silent period a line is drawn on the map at right angles to the direction of the loop. This line indicates the direction from which the sounds are coming. This takes place at the same time at all three stations, and where the lines on the map intersect is the point where the offender can be found."
"But I suppose that location isn't very exact, is it?" asked Bob.
"No; but it's usually exact enough," said Brandon. "We go to the place indicated on the map, and look about in the neighborhood for aerials. Anybody owning them has to show his license, if he has one, and if he hasn't—well, that's the man we're after."
"Simple enough," commented Bob. "But when you don't know how it's done, it seems like looking for a needle in a haystack."
"Yes, and by all the rules it should be easier than usual to locate this offender," said the radio inspector, "because he has a peculiarity that marks him out."
"I'll bet I know what it is, too," said Bob quickly.
"You do?" said Brandon, surprised.