Carl & Jerry: Electronic Shadow
September 1957 Popular Electronics
Popular Electronics began publishing a monthly electronics detective story series soon after its debut in 1955. The two main characters, Carl and Jerry, helped keep the world safe from miscreants by way of their investigative prowess and deductive skills. The Hardy Boys were amateurs in comparison (wait, they were amateurs). The theme and ultimately solving of each mystery centered around use of electrical and/or electronics. If you enjoy short stories, then you will like the Carl & Jerry series. I will be posting more of them as time permits.
September 1957 Popular Electronics
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Carl & Jerry: Electronic Shadow
By John T. Frye
Mrs. Bishop had told Chief of Police Morton that Carl and Jerry were out
in the back yard; and that is where he found them, busily engaged in fastening a weird-looking object to the luggage carrier of Carl's bicycle. The Chief stood for a moment unnoticed and then walked over to where the two were working.
"Hi, boys," he greeted them. "What are you up to?"
The boys glanced up with the startled, retrospective look the unexpected sight of brass buttons and blue serge usually evokes from boys their age, but their faces broke into welcoming grins as they recognized Mr. Morton.
"Hi, Chief; we're just getting ready to tryout a new gadget we've been working on," Carl explained. "We call it 'the electronic shadow.'''
"'Electronic shadow,' huh? Sounds as though you two might be trying to muscle in on my job. But let's have the details - how does it work?"
"Basically," Jerry explained, "the thing is a small working model of a gyro-compass. It consists of this gimbal-mounted gyroscope that has its heavy but carefully counterbalanced and easily turning rotor driven at high speed by this battery-operated electric motor here on the end of the rotor shaft. The mounting and weighting are such that the axle of the rotor is always maintained in a horizontal plane in spite of any tilting of the surface on which the compass rests. Under these conditions, the spinning axis of the rotor will align itself with the axis of the earth in such fashion that both the rotor and the earth are turning in the same direction. One end of the rotor shaft will continually point north no matter how the object on which the compass is sitting is turned about.
"Next, note this small variable resistor mounted here on the frame supporting the gyroscope mounting. It looks like an ordinary radio volume control, but there are important differences. For one thing, the shaft of this variable resistor can be turned around and around without meeting a stop. You can see that it only has two terminals. One terminal is connected to one end of the resistance element; the other goes to the slider that contacts this element. As the shaft is turned, the resistance appearing between the two terminals rises gradually from zero to a maximum value and then falls abruptly back to zero with each complete rotation.
"You can see here that the shaft of the variable resistor is fastened to the gimbal holding the spinning rotor. Watch what happens as Carl turns the bicycle around. See: the shaft is maintained in the same position by the gyroscope, but the resistor case itself turns with the bicycle. That means that a different value of resistance appears between the terminals for every point of the compass at which the bicycle is pointed.
"The variable resistor is connected in the circuit of a transistorized resistor-capacity type audio oscillator. The frequency of this oscillator varies as the resistance of the compass-controlled resistor varies. That means that as the bicycle is pointed in different directions, different tones are produced by the audio oscillator. This oscillator modulates a small transistorized transmitter whose signal can be picked up on a receiver down in the laboratory.
"Down there, too, is an identical audio oscillator containing a matching variable resistor. The shaft of that resistor is locked in the same position as that of the one up here which is controlled by the gyroscope. An arrow is fastened to the resistor case. When that arrow points in the same direction in which the bicycle up here is pointing, the tone coming from the receiver and the one coming from the oscillator down there are at exactly the same pitch. If I want to know which way the bicycle is pointing at a given instant, all I have to do is swing the arrow around until the tone of my audio oscillator matches that coming from the receiver and note the direction in which the arrow is pointing."
"WHEW!" Chief Morton exclaimed, mopping his brow. "I think I follow you, but it isn't easy for a duffer whose knowledge of electronics is confined to how a flashlight works. What does that little wheel riding on the rear tire have to do with it?"
"That's our distance-traveled indicator," Carl chimed in. "The little wheel turns a flexible shaft that works a gear train. A cam on a shaft of this gear train closes a pair of contacts momentarily every tenth of a mile and modulates the little transmitter with a high-pitched 'beep' produced by another transistorized audio oscillator. This allows the fellow down in the lab to keep track of the direction and distance the bicycle has traveled at all times."
"Come on down to the lab and let's see if we can keep track of where Carl is riding," Jerry invited.
"Fine," Chief Morton agreed with an eagerness that seemed a little strange in one who had no knowledge of or interest in electronics.
Jerry had a map of the city spread out on the workbench of the basement laboratory. He flipped on the receiver and the audio oscillator, then pecked on the basement window and motioned for Carl to take off.
"He's heading south," Jerry announced, as he turned the arrow so that the two tones were alike. There was a loud beep from the receiver. Jerry picked up a plastic map-measuring instrument and put the little roller wheel on the map at a point just south of where they were.
"This map is drawn to a scale of ten-inches-to-the-mile, and I have this map-measuring gadget set to that scale," he explained. "Every time we hear a beep, I'll roll it along the direction we know Carl is traveling until it shows a tenth of a mile. That way we should be able to keep track of where Carl is at all times."
Doing this turned out to be easy, because Carl rode along streets that were laid out in a rectangular pattern. When he turned, it was usually at right angles, producing an abrupt change in the tone coming from the receiver. When this happened, Jerry simply swung the arrow until the tones were again in step and changed the direction in which he was moving the map-measurer to agree. All at once, though, the sound coming from the speaker began to sound like: "Baweek, baweek, baweek."
For a moment a worried frown crossed Jerry's round face, then he broke into a grin. "The smart aleck is riding around in a circle at this street intersection," he said, pointing at the map. A little later the indication showed that Carl was riding straight for home. When the map-measurer had crawled back to the starting point, Chief Morton opened the basement door just in time to hear the squeak of Carl's brakes outside.
"That was a wonderful performance, boys," the chief said as Carl came down the steps into the laboratory. "Now, as you may have guessed, I had a problem on my mind when I came over here; but I'm almost convinced you two have come up with the solution before even hearing the problem. To be sure, though, I have one question: do you think that 'electronic shadow' will work as well in a car as it does on the bicycle?"
Jerry wrinkled his brow a minute and then answered slowly, "I can't see why not. The distance-traveled roller could be driven from one of the car wheels. The diameter of the roller would probably have to be changed so that the distance indication would be accurate. But what do you have in mind?"
"Here's the story," the chief began. "Remember about a month back when a bank bandit held up the First National Bank and got away with forty-seven thousand dollars? If you do, you'll recall that we nabbed him with a roadblock about thirty minutes after the robbery was committed; but he didn't have any of the actual cash with him. Only some bonds were found on him. Somewhere here in town he had hidden the cash. He's a pretty tough cookie, and nothing we can do will make him tell us where the money is hidden. We had just about given up on this guy but something came up recently that makes us think we may have a chance of uncovering the loot after all.
"A couple of days ago, a guard at the jail came to us with the story that this bandit - his name is Palmer - had promised him half of that forty-seven thousand if he would arrange a jail break. All the guard has to do is to allow Palmer to overpower him and have a car waiting in the alley behind the jail.
"We're of half-a-mind to go along with this jail break in the hope of making Palmer lead us to the missing money. The guard is willing to cooperate with us for a share of the reward offered by the bank for the recovery of the money. The hitch is that we're afraid of losing Palmer and the money, too! We're pretty sure he hid it somewhere around those refining plants at the south edge of town. As you know, there are acres of ground out there covered with huge steel tanks, steel towers, etc., all of which reflect radio waves like mad. These reflections make the kind of direction-indicating equipment we used on those car thieves useless. A trial run proved that to us, for we lost the test car completely when it got near the refineries. But I've got a hunch that this electronic tattle-tale of yours would keep the finger right on Palmer. With it, all we have to do is hear the signal without worrying about whether the signal heard is a reflection or not."
"Sure it will work!" Carl exclaimed, eager for the excitement to come.
"Let's make a test and see," Jerry suggested more cautiously.
So they did. They installed the compass in the car that Palmer would be driving if the scheme were carried out, and this car was driven all over town while the two boys and Chief Morton kept track of it at police headquarters. When the record the driver kept of his course was compared with that plotted on the map at the police station, the two records were found to agree in every minute detail.
"I'm sold!" Chief Morton announced. "We'll arrange the jail break for tonight around midnight. You two boys be sure and be here around eleven. I'm going to have every man I can on duty. Men on foot equipped with hand transceivers will be scattered all around the refinery district. We'll have to depend on one of them being close when Palmer gets out of the car to pick up the money. We can't crowd him too closely with the squad cars or he'll get suspicious; but we can keep them in a circle around him to make sure he doesn't slip through our fingers. If that happens, this town will have a new police chief in short order."
Carl and Jerry, of course, were at the station by ten o'clock. The chief explained that the guard had arranged with Palmer for the break to occur at exactly midnight. A relay had been connected to the ignition switch to turn on the "electronic shadow" when the motor was started and to cut the transmitter off when the motor stopped.
As the clock hands scissored together at the top of the clock face, tension mounted around the large map of the city spread out on a table near the radio dispatching position in the police station. Carl was to operate the receiver and the direction-indicating arrow of the audio oscillator. Jerry was to keep track of the car on the map. A policeman with a stop watch was to keep a record of the time intervals elapsing between the tenth-of-a-mile beeps. Chief Morton would move between the map and the dispatcher so as to keep all forces coordinated for fast, smooth operation.
It was just six minutes after midnight when the audio tone suddenly burst from the receiver in front of Carl. The fish had taken the bait!
The practice sessions paid off, and soon the boys were easily keeping track of the car. Chief Morton, bent over Jerry, could see that Palmer was driving an aimless course about town, apparently trying to throw any possible pursuit off his trail. Before long, though, he started driving straight for the south edge of the city. The chief kept a wide circle of squad cars around the position indicated on the map by the crawling map-measurer in Jerry's hand.
As Palmer reached the vicinity of the refineries, the car seemed to have slowed down, for there was an exceptionally long interval between two of the beeps. Then he apparently turned down a side street, drove for about a block, and cut off the motor. At any rate, the signal from the receiver disappeared.
Chief Morton sprang into action with a volley of commands intended to focus all his forces at the spot where the car had stopped, but to keep them out of sight.
Suddenly there came from the speaker of the police radio the chilling report, "There's no car here, Chief."
For a long, long minute, Jerry and Chief Morton stared at each other in dismay. Then Jerry suddenly reached over and grabbed up the sheet of paper on which the policeman had been keeping a record of the time intervals between beeps.
"That long interval!" Jerry exclaimed, and looked again at the map. "We thought he was just driving slowly, but I'll bet he accidentally went past this alley, then stopped and backed up. That means that the practice sessions paid off; soon the boys were easily keeping track of the car. Chief Morton could see that Palmer was driving aimlessly instead of being parked on this street here, he is really parked in the alley ... "
Before the boy finished speaking, the chief of police had instructions crackling through the air. It was only seconds until the reassuring word came back, "The car is here all right. Palmer is just getting out of it and walking over to the side of a warehouse. He's digging around in the sand with the toe of his shoe. Now he's lifting out a tin box. Stand by. We're going to grab him!"
And grab him they did. The box contained the entire amount of cash taken from the bank. As a squad car was bringing Palmer back to the jail, the chief explained to the boys that they would undoubtedly receive a part of the reward.
"That's dandy," Carl remarked; "but our folks will just sock it away in the bank for our college education. What gives us our kicks right now is the satisfaction of knowing that for once we dreamed up a gadget that really worked."
"You mean some of your inventions don't work?" Chief Morton asked in wide-eyed wonder. "That's hard to believe. You're batting 1000 with me. I've called on you twice, and both times you came through."
"Come on, Blabbermouth; let's go home," Jerry said, taking Carl firmly by the elbow and steering him toward the door. "You're so tired and sleepy you don't know what you're saying. Good night, all," he called cheerfully back over his shoulder as he hustled Carl out the door.
"He's lifting out a tin box. Stand by. We're going to grab him." And grab him they did. The box contained all the cash taken from the bank ...
Carl & Jerry: Their Complete Adventures is now available. "From 1954 through 1964, Popular Electronics published 119 adventures of Carl and Jerry, two teen boys with a passion for electronics and a knack for getting into and out of trouble with haywire lashups built in Jerry's basement. Better still, the boys explained how it all worked, and in doing so, launched countless young people into careers in science and technology. Now, for the first time ever, the full run of Carl and Jerry yarns by John T. Frye are available again, in five authorized anthologies that include the full text and all illustrations."