September 1957 Popular Electronics
[Table of Contents]People old and young enjoy waxing nostalgic about
and learning some of the history of early electronics. Popular Electronics was published from October 1954 through April
1985. All copyrights are hereby acknowledged. See all articles from
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.
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
"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
"'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
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
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
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
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."
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
"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 ...
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."
Carl & Jerry Episodes on RF Cafe
- Abetting or Not? - October 1956
- Electronic Beach Buggy - September
- Extra Sensory Perception
- December 1956
- Trapped in a Chimney
- January 1956
- Command Performance -
- Extracurricular Education,
- Treachery of Judas, July 1961
- The Sucker, May 1963
Stereotaped New Year, January 1963
- The Snow Machine, December 1960
Extracurricular Education, July 1963
- Slow Motion for Quick Action, April
- Sonar Sleuthing, August 1963
TV Antennas, August 1955
Succoring a Soroban, March 1963
"All's Fair --", September 1963
Operation Worm Warming, May 1961
The Crazy Clock Caper, October 1960
Two Detectors, February 1955
Tussle with a Tachometer, July 1960
- Therry and the Pirates, April 1961
The Sparkling Light, May 1962
Pure Research Rewarded, June 1962
Hot Idea, March 1960
- The Hot Dog Case,
- A New Company is Launched,
- Under the Mistletoe, December
- Electronic Eraser, August 1962
- Blubber Banisher, July 1959
"BBI", May 1959
Ultrasonic Sound Waves, July 1955
The River Sniffer, July 1962
Ham Radio, April 1955
El Torero Electronico, April 1960
Wired Wireless, January 1962
Electronic Shadow, September 1957
Elementary Induction, June 1963
He Went That-a-Way, March1959
Electronic Detective, February 1958
Aiding an Instinct, December 1962
Posted April 17, 2012