February 1958 Popular Electronics
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Long before their college days at Parvoo U., our two amateur
electronics sleuthing buddies were on the job tracking down
and trapping bad guys by using their combined knowledge of circuits
and physics. In this episode, Carl and Jerry are tasked with
helping a hobby store owner stop a rash of thefts that always
seems to occur during a busy time right after school lets out
for the day. Their first inclination was to devise a system
like the big department stores were installing that used passive
tags on items that would trigger an indicator when passed through
the detector at the exit door. That was in 1958
(the year I was born, yikes!)
when the anti-theft tags were first being utilized. Unfortunately,
the system they were able to build was not sensitive or selective
enough, so they came up with a different scheme that helped
the storekeeper nab the perp. It was quite elementary, as a
world-famous detective was fond of saying.
Carl & Jerry: Electronic Detective
By John T. Frye
A February snowstorm was swirling around outside as Carl
Anderson came stamping into the basement laboratory of his friend,
Jerry Bishop. His horn-rimmed glasses instantly steamed over
in the warm room, and when he took them off he saw that Jerry
had company. A pleasant-featured young man was sitting on the
worn leather sofa watching Jerry doing something at his workbench.
"Hi, Carl; this is Mr. Singer who owns that hobby shop at
Fifth and High," Jerry announced. "He's got a problem."
"Glad to know you, Carl," Mr. Singer said, as he stood up
and shook hands. "I've got a problem all right. Shoplifters
have really started working me over. As you know, our merchandise
is mostly on open display so that the youngsters who make up
a large part of our trade can handle it. That makes it easy
picking for anyone so inclined. Naturally we expect some losses
of this nature, but recently they've become serious."
"What sort of things are snitched?"
"Everything from a bicycle on down!
However, that fancy cap pistol Jerry has over there on the
bench seems to be a favorite. We've lost a couple of dozen of
those since school started."
"Then it must be children doing it." "That's right; and that's
what makes catching the sticky-fingered person such a ticklish
proposition. Maybe I'm a softy, but I don't want to call the
police in on this and maybe send some kid to reform school.
I just want to find out who's doing it and put a stop to it.
I feel I have to show the kid doing it that no-one gets away
with what he's pulling for long; otherwise he may develop into
a real criminal."
"Don't you keep an eye on things?"
Everything was built on a flat sheet of Bakelite
that fitted easily beneath the cardboard shelf to which the
pistol was securely fastened.
"We try, but you can't appreciate what a job it is until
you see the after-school crowd that jams into our store. We
have all we can do waiting on trade, stopping scuffling, etc.,
without trying to watch all the counters and aisle displays
at once. And the thief is pretty crafty. We thought we could
stop the loss of the pistols by wiring them in their boxes;
but they kept right on disappearing, box and all!"
"Carl, you're just in time to help me try something," Jerry
interrupted. "I read the other day that some big department
store had installed an electronic shoplifting detecting device
that was triggered whenever a special price tag, actually a
miniature printed tuned circuit, was brought near it. Price
tags were removed from all merchandise when sold; so if anyone
tried to carry something off without buying it, the electronic
gadget would squeal on him.
"I figure the detecting device must be simply a glorified
grid dip oscillator such as the one I have here on the bench.
As Carl knows but possibly you don't, Mr. Singer, a 'GDO,' as
we call it, is simply a vacuum-tube oscillator with a meter
that reads the rectified grid current which flows from the tube
grid to ground as long as the tube is oscillating. The amount
of grid current is proportional to the vigor of oscillation.
Whenever another circuit tuned to the frequency at which the
GDO is oscillating is brought near the coil of the oscillator,
this tuned circuit absorbs energy from the oscillator by induction.
This cuts down on the vigor of oscillation and produces a reduction
or 'dip' in the current reading of the meter."
"I see that this loop of wire strung around the door frame
is replacing the coil ordinarily plugged into the GDO," Carl
"That's right. And this little coil-and-capacitor combination
is tuned to the frequency at which the grid dip oscillator is
working. I want you to walk back and forth through the door
without it first - then again with it in your hand."
As Carl made the last trip, Mr. Singer walked over and watched
"The pointer moved!" he exclaimed.
"Yes, but not enough I'm afraid," Jerry said. "I was hoping
we'd get a really strong kick that would operate a sensitive
relay. And there was a current change caused by body capacity
effect when Carl went through the loop without the tuned circuit.
Probably we could get away from that by housing the loop of
wire in some sort of Faraday shield which would stop capacity
effects without interfering with magnetic induction ... and
we could amplify the grid current change with a d.c. amplifier
until it would kick a relay. But I'm afraid all that wouldn't
be practical for just this one job."
"Well, I'm sorry you can't help, but I certainly appreciate
your trying," Mr. Singer with obvious disappointment as he began
buttoning his overcoat.
"Wait a minute!" Jerry exclaimed. "We don't give up that
easily. I've got another idea that should be sure-fire."
"Let's hear it," Mr. Singer said, sitting down again.
"Well, I've been looking at this cap pistol carton, and I
see there's plenty of room beneath the cardboard insert that
holds the pistol for us to conceal a transistorized, tone-modulated
transmitter. This will have a range of only about 50 feet; so
if the pistol is placed on a counter at the rear of your store,
the signal won't be heard on the receiver we'll place near the
front door - with an antenna lead from the receiver fastened
around the door frame. However, if anyone tries to carry the
pistol and transmitter through the door, the signal from the
transmitter will be heard very loudly in the receiver."
"Sure it will work?" Mr. Singer quizzed. "Sure I'm sure,"
Jerry said confidently.
"Carl and I have played around with these transistorized
wireless mike circuits a lot, and we know how to build them
and what they will do. Suppose you don't display the cap pistols
for a couple of days while Carl and I build up the transmitter
and check it out. Then you can put this special one on display,
and the kid pinching them will probably snap it right up."
"That's exactly what I'll do," Mr. Singer agreed. "Just let
me know when you're ready."
The door had hardly closed behind him before Carl and Jerry
were busy laying out the little transmitter. There was no problem
with the circuit, for all they had to do was combine a transistorized
"wireless mike" transmitter and a simple transistorized audio
oscillator. The audio oscillator replaced the microphone of
the transmitter and modulated the output with a steady tone
of about 500 cycles per second. The transmitter was set to work
on an unused area near the low end of the broadcast band so
that an ordinary radio could be used to pick up the signal.
Everything was built on a flat sheet of Bakelite that fitted
easily beneath the cardboard shelf to which the pistol was securely
When the equipment was working to their satisfaction, the
boys contacted Mr. Singer; and that evening the three of them
went down to the store and set up "Elmer, the Electronic Flatfoot,"
as Carl insisted on calling it. Everything worked exactly as
Jerry had predicted. It was agreed the boys would rush right
to the store from school the next day and that Mr. Singer would
not put out the pistol until they arrived.
It seemed as though school would never let out the next afternoon,
but when it finally did Carl and Jerry really hot-rodded their
bikes down to the store. Mr. Singer was waiting for them. Jerry
switched on the hidden transmitter, and the "bait" was provocatively
Almost immediately the store began to fill with a crowd of
shouting, shoving, noisy boys. Jerry and Carl stayed near the
front of the store and deliberately avoided even looking at
the counter holding the cap pistol. Mr. Singer, his wife, and
two clerks were busy waiting on customers.
Removing the receiver from his shirt pocket,
he used it as a search wand to go over each one.
A good half hour passed without anything happening. The boys
were just beginning to think that no one was going to try to
make off with the pistol when they heard a weak musical tone
in the receiver. Steadily it increased in strength. Mr. Singer
heard it and came over to stand by Carl and Jerry. As two well-dressed
boys carrying school books went through the door, the tone reached
a very loud level and then began to subside.
Mr. Singer called after them: "Say, fellows, come back here
a minute. I want to talk to you."
The two schoolboys exchanged a long look and then slowly
came back to the store. As they crossed the threshold, the receiver
once more built up to a peak of sound.
"Come on back to my office," Mr. Singer said.
They walked back with him, tossing their books on an empty
counter as they went past. Carl and Jerry followed, and for
the first time Carl noticed that Jerry was wearing his little
shirt-pocket transistor receiver with its earphone tucked in
his ear. Carl also noticed that as Jerry walked along just behind
the two boys he kept fumbling with the tuning control of this
receiver, and his face had begun to wear a puzzled, worried
"I was going to use this to tell which one had it," he whispered
to Carl, "but I can't pick up the signal near either of them!"
"Maybe the transmitter's gone dead," Carl suggested.
"Nope, I can still hear it faintly on that receiver up front,"
Jerry observed as they reached the door of Mr. Singer's office.
"You tell Mr. Singer to stall," he said desperately, "while
I see if I can find what's gone wrong."
As the rest of them filed into the office, Jerry turned around
and started walking slowly toward the front of the store, tuning
his little receiver back and forth across the low end of the
broadcast band as he did so. Suddenly he began picking up the
tone signal, but after he had walked about two-thirds the length
of the store it began to fade out again. Backtracking, he found
that the signal reached a peak when he was standing by the books
the boys had tossed on the counter. He quickly spread the books
out on the counter. Removing the receiver from his shirt pocket,
he used it as a search wand to go over each of them. One large,
fat volume on ancient history gave out a very loud signal.
Jerry opened the book and made an astonishing discovery.
The first and last few pages of the book were intact, but the
center of all the middle pages had been cut out. Inside this
opening was the cap pistol still wired in its box.
He picked up the book and, holding it behind him, stepped
into the office.
"Which one of you boys is named William Palmer?" Jerry demanded.
The boy with dark auburn hair and freckles spoke up hesitantly:
"Then this must be your book with your name in the front
of it," Jerry said quietly as he placed the book on the desk
in front of Mr. Singer and opened it.
The Palmer boy's face turned so deathly white that his freckles
seemed to stand out in three-dimensional style.
"I didn't really mean to steal," he stammered. "Honest, I
didn't. It just seemed a kind of game, and the other fellows
kept egging me on. Are - are you going to send me to jail?"
"Come on, Carl," Jerry said as he headed for the door.
Carl followed, but even after the door was closed behind
them Carl and Jerry could still see the pale frightened faces
of the two boys and the stern serious look on the face of Mr.
"What do you suppose Mr. Singer will do with them?" Carl
"I'm not sure, but it will be what's best for the boys,"
Jerry declared with conviction. "They just don't know how lucky
they are that they were caught by a fine man like Mr. Singer.
You can bet he'll not let them off too easy. From the looks
on their faces, though, I think they've already learned their
"But they'll never know it was Elmer, the Electronic Flatfoot,
who put the arm on them!" Carl said with a grin.
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."
Carl & Jerry Episodes on RF Cafe
- Carl & Jerry: Anchors Aweigh, July 1956
- Bosco Has His Day, August 1956
- The Hand of Selene, November 1960
- Feedback, May 1956
- Abetting or Not?, October 1956
- Electronic Beach Buggy, September
- Extra Sensory Perception, December
- Trapped in a Chimney, January 1956
- Command Performance, November 1958
- Extracurricular Education, July
- Treachery of Judas, July 1961
- The Sucker, May 1963
- Stereotaped New Year, January 1963
- The Snow Machine, December 1960
- Extracurricular Education, July
- Slow Motion for Quick Action,
- 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
- A Hot Idea, March 1960
- The Hot Dog Case, December 1954
- A New Company is Launched, October 1956
- Under the Mistletoe, December 1958
- 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 September 17, 2014