Who Killed the Signal?
1943 QST Article
this amazing electronics allegory was written by then-QST-editor
Clinton B. De Soto!
February 1943 QST
articles are scanned and OCRed from old editions of the ARRL's QST magazine. Here is a list
of the QST articles I have already posted. All copyrights are hereby acknowledged.
Who Killed the Signal?
A Radio Mystery Serial
By Clinton B.
De Soto,* W1CBD
Chapter 1 - "The Thin Man"
If you're a newcomer to the game, it may seem that radio theory
already has enough mystery without adding more. True, the technical
journals - even QST, sometimes - do make it a mysterious subject
with their textbook language and complex notations.
isn't really any more mysterious or complex than many a detective
story - at least not after you've read the last page and know "whodunit."
The difference lies in the method of presentation. There may be
some utility, then, in the idea of presenting radio fundamentals
in the manner of detective fiction.
That's what this is
- a series of radio lessons in the guise of a detective-mystery
yarn. Instead of human characters we'll use another kind - but we'll
try to make the characterizations true and the background and incident
realistic. Our purpose is to divert and entertain you, and perhaps
amuse you a little. And if, by accident, you happen to learn something
from this series - if it helps to clarify your understanding of
basic radio theory - well, that's all right, too.
radio receiver stood silent and dark in the dimly-lighted corner.
In other days it had been a thing of vibrant life, its ornate window
brilliantly illuminated with a rich, golden glow. From its recesses
spoke miscellaneous voices crisp, mellow, inveigling, brusque,
authoritative, shy. Sometimes the flute-like notes of code skittered
brightly from its tightly-curtained front, and now and then sparkling
music poured forth melodiously.
But that was before. Now
the receiver stood in forlorn neglect. Dust gathered on its metal
cover, and a spider spun suspension cables for his web between its
louvers and the wall. The receiver did not much care; indeed, it
had no way of knowing. For the heart had gone out of it. The Signal
That was the mystery the Great Sleuth faced when he was called in
on the case - who killed the Signal?
Even from the
start it was apparent that this was one of the toughest cases of
his career. The Great Sleuth was an amateur, but that implied no
reflection on his ability. Any loyal detectivestory reader knows
that the amateur sleuths from Sherlock Holmes down to Nick Charles
are better than the professionals (and if, like Nick, they are
professionals turned amateur or vice versa, that only makes them
Like any good detective, the first
thing the Sleuth did was survey the scene of the crime. Blowing
the dust off the receiver's metal cover, he lifted the lid and peered
inside. It was of twostory construction. Upstairs, on top of the
metal floor called the chassis, lived the larger occupants - an
odd assortment of characters with equally odd names. These characters
belonged neither to the animal nor vegetable kingdoms, but to a
special classification of fauna called "parts."
of these parts seemed to be members either of the Condenser or Transformer
families. There was Tuning Gang - he was the head of the Condenser
family, of course - and an upright cousin called Filter. Then there
were Power, Intermediate Frequency (invariably called LF. by his
buddies in the shop), and Audio Output all Transformers. Tuning
Gang had a business associate named Tuning Dial who lived there
with him. Output Transformer lived in another small house nearby
with his inseparable pal Loud Speaker.
A strange thing
about the chassis set-up was that most of its occupants had very
little to do with each other directly. Instead, they had a flock
of servants called Tubes who carried things back and forth between
them. These Tubes seemed to be everywhere - half a dozen or more
of them. Mostly they were dressed in neat black outfits, but a couple
of the biggest Power Tube and Rectifier Tube - wore gleaming glass
Downstairs there was a motley collection of smaller
characters. These the Sleuth was at first inclined to dismiss, but
he reflected that it is usually the most unsuspicious character
in a mystery story who turns out to be the guilty party, and so
he looked them over, too.
were too many of these little fellows for the Sleuth to remember
all their names, but he noted that quite a few were lesser members
of the Condenser family - R.F. By-Pass, Mixer Coupling, Oscillator
Trimmer and so on. Most numerous of all were the Resistor family;
there were dozens of these tough little fellows. Over near the back
there was a mysterious, solitary character called Filter Choke.
Finally there were a number of minor parts - Sockets, Switches,
Terminals, and in a corner a lean, Gary-Cooperish fellow called
Power Cord and his assistant, Power Plug.
the Sleuth noticed was that a certain social order seemed to exist
among these parts. Most members of both the Resistor and Condenser
families used the title "Fixed" before their names, for example.
The most distinguished, however, were called" Variable" - approximately
equivalent to "Honorable" as opposed to plain" Mister," he supposed.
The Sleuth looked each part over carefully, but he
saw none that seemed an obvious suspect. Finally he called together
his trusted assistants - Ohm Meter, Volt Meter, and their attractive
sister Milly AmMeter - and took them over into the corner. There
they held a conference in whispered tones.
one of those blanked color-coded Resistors, I'll bet," Ohm Meter
muttered before anyone else could speak. Sleuth listened tolerantly.
Ohm was a mighty valuable man, but quick to jump to conclusions.
It was a toss-up as to whether he or Volt Meter was the most valuable;
but Sleuth knew he could count on either when he needed to verify
a connection. Milly was the one who gave him the most concern -
she was a sensitive creature, but she had little resistance and
Sleuth was always afraid that she would get mixed up with a load
beyond her range and burn out.
"Now let's go at this
thing in a logical way," Sleuth restrained them. Milly was already
beginning to tremble. "There are a lot of suspects here, and the
only way we can track down the guilty one is to investigate them
one by one.
"First of all, though, we've got to decide
if this really was murder. Could it have been an accident - something
like a loose connection, you know?"
"Well, there's the wiring
-" Ohm said doubtfully. "But I'm a pretty good judge of continuity
and if there was anything wrong I'd know it. I can spot a bad joint
before I ever open the door!"
Sleuth was pensive. "You're usually right, at that," he said. "OK
- for the present, at least. Now for the next point - how do we
know that it was an inside job? Could an outsider have had anything
to do with it?"
There was a moment's silence, and
then all three started talking at once. The Sleuth held up his hand.
"All right - all right! I'll say it for you. There are three entrances
to the chassis, which means three places where an outsider might
have got to the Signal."
He counted on his fingers.
"One, there's the outlet Power Cord uses to take in the family power
supply. Two, there's the cable path between the chassis and the
housing where Output Transformer and Loud Speaker live. Three, there's
the little service terminal where Antenna makes its deliveries."
"Which do we tackle first, boss?" Volt Meter asked
alertly, his pointer quivering with eagerness.
as well take them in order," Sleuth replied. "Let's have a talk
with Power Cord first."
Leaving the rest of the parts
to wonder what was happening, they went over to the rear of the
Power Cord was a thin, elongated character
with a chocolate-brown complexion. He was more than willing to talk.
"Sure, I knew the Signal was dead," he told them eagerly.
"I knew it the minute everything went quiet and all the noise stopped."
He lowered his voice. "It all sounds like noise to me," he added
"Can you tell us anything more?" Sleuth
"Well, I remember that about that same time
the current stopped coming the way it always did. I don't know for
sure whether it was just then or a little later, but it was about
the same time."
did you know?"
"Why, I have to carry the current to
the set," Power Cord answered in some surprise. "Naturally I'd know
when I didn't get any."
"That's your job, is it?" Sleuth
asked. "To deliver current to the rest of the set?"
right. And it's an important job, too.
Why, they have to have
that current in just the right cycles and everything. If they don't
get it - well" His voice dropped to a whisper. "Do you know what
I think? I think the Signal died from electron starvation, just
because there wasn't any current!"
Sleuth looked at him carefully.
"Maybe you'd better explain all about your job here and the current
and so on."
"Well," Power Cord began, "it's all very
simple. This whole set here needs current - no current, no play.
Current is our food. It's all filled with little electrons - vitamins,
maybe you'd call 'em. You want me to tell about the electrons, too?"
The Sleuth nodded. Power Cord sighed, and said, "I
guess I'll have to start from the beginning then.
"Even if you don't know about electrons, you must have heard of
molecules. They're the the smallest units to which anything - wood,
metal, water - can be broken down. Everything is made up of molecules
- I am, and you are, too. These molecules are made up of various
combinations of atoms, which are the basic chemical elements.
Every substance known is made up of various combinations of these
atoms. There are more than 90 varieties of them.
part's simple enough, but here's where it gets tougher. When you
try to go inside the atom in order to learn what it is made of,
you leave the field of solid physical matter and must think in terms
of force. For atoms are made up of electrons, and electrons, as
you might guess from their name, are nothing more or less than electrical
charges -little bits or particles of energy or force. Each atom
contains a number of these electrons, together with a nucleus; the
electrons are believed to rotate about the nucleus much like the
planets about the sun.
"The nucleus, in turn, is made
up largely of protons and neutrons. The protons are the opposite
of electrons; they have a positive charge, while the electrons have
a negative charge. There is also a large difference in the mass
of the two - the proton being about 1860 times heavier than the
electron. The neutron has the same mass as the proton but has no
"That's all well enough, but what has it
to do with who killed the Signal?" Ohm Meter interrupted impatiently.
"Plenty - wait and see," Power Cord replied. The
Signal was no different from the rest of us - it was made up of
electrons, too. And it needed more electrons all the time to live.
You see, the Signal was an electric current."
then? You've been talking about it enough."
it this way. You might know that when two permanent magnets are
placed together with the north and south poles facing they exert
a mutual attraction. In the same way, a positively-charged nucleus
attracts negativelycharged electrons. In many substances the attraction
is so great that the electrons are rigidly held and can be knocked
off only with great difficulty. In other substances, however, the
electrons are not so strongly attracted, and it is fairly easy to
knock them off. If an electron is dislodged from an atom in one
of these substances, this atom in turn attracts a new electron
from a neighbor, and the neighbor from its neighbor down the line,
and so a regular chain of motion is set up. This motion of the .
electrons is called electric current."
Meter seemed out of his element, but Milly's response could be read
on her face.
"Now," Power Cord continued, ','you'll
have noticed that only in some substances did I say that this movement
of electrons occurred with relatively little resistance. Such substances
are known as conductors, because they find it easy to conduct electric
current. These materials include most of the metals, especially
silver, copper, aluminum and steel. I'm made of copper inside and
I'm a conductor," he asserted proudly.
"In other substances
the electrons are so firmly fixed in their atoms that they can be
moved only with great difficulty, and little or no electric current
can flow. Such materials are known as dielectrics or insulators.
They are useful, too, because they can be used to insulate electric
currents by being placed between the conductors of those currents.·
Bakelite, ceramics, wood, rubber, air - these are good insulators.
My skin is rubber, you see, and these other parts around here wear
some of the other insulators such as Bakelite and ceramics."
The Sleuth's face was impassive. "That's all very interesting, but
I don't see that it gets us anywhere," he replied. But Milly begged,
"Tell us more about the electric current."
yes. Well, as I was saying, there are two kinds of current. There's
direct current, or d.c., which means that the electrons move steadily
in one direction. Not in a constant stream, you understand, but
jumping from one atom to the next and knocking other electrons loose
when they land.
"D.c. is useful enough in its way. Lots of
parts can't live without it. But it's not II:s readily available
as a.c. - you have to get it from things like batteries and generators,
you know - and so the kind of power we get to start with is a.c.
For those that need it we make d.c. from the a.c."
us about a.c.," Sleuth commanded.
"A.c. is alternating
current. That's the kind I carried. In it electrons change direction
all the time, at regular intervals. At one instant the current flows
in one direction and at another instant in the opposite direction.
Of course, when the current changes direction the polarity reverses
from positive to negative or vice versa. Each complete change of
direction - from plus to minus, say, and back again - is called
a cycle. The rate at which it changes is known as the frequency
of the current. The polarity of the house-lighting current they
get from me reverses 120. times each second; that makes its frequency
60. cycles per second."
"And the Signal has to have this
kind of current to live?" the Sleuth asked.
"Well, not exactly,"
Power Cord hedged. "But the set has to be supplied with it to keep
the Signal alive."
"However, you claim it was because
the current was no longer available that the Signal died," Sleuth
"I do," Power Cord answered firmly.
The Sleuth pounced. " Well, then, since it was your job to deliver
this current and you didn't do it, you're responsible for the Signal's
death!" he charged.
Power Cord writhed in denial.
"Oh, but you don't understand," he wailed. "It wasn't my fault that
I couldn't deliver the current. I just couldn't get any. There wasn't
any coming from the wall outlet!"
"How do you explain that?"
Sleuth probed. "I can't," Power Cord answered in a defeated tone.
"It always was there, as much as was needed. Before this I was always
charged up full, ready to conduct whenever A.C. Switch up there
closed the circuit."
There was silence for a moment.
Then a speculative look came over Volt Meter's face. Suddenly he
"I think I've got it," he announced. "If
Power Cord isn't lying, there's only one reason why he hasn't been
getting enough electrons to feed the set. That's because a certain
part hasn't been doing his job!"
A few seconds later
he returned, dragging a prisoner behind him. It was Power Cord's
squat little helper, Power Plug. "Do you know what?" Volt demanded.
"This fellow wasn't even in his socket. He was lying on the floor
taking a nap!"
"Hmmm!" The Sleuth glared sternly. "Maybe
not murder, but certainly manslaughter. What have you got to say
for yourself? "
"P-please, mister, it's not my fault," Power
Plug whimpered pleadingly. "The Signal was already dead when I left
my receptacle. Honest - I would never have left otherwise."
The Sleuth looked at him keenly. "Well, there's one way to find
out. Go down there and plug yourself in, Plug, and we'll see. Volt,
you'd better go with him."
A few moments later Power
Cord seemed to come to life again. "The current - there's the current!"
he shouted, "Hey, up there - you A.C. Switch. Close yourself and
let's get going!"
Twenty seconds later his face fell
again. "It's no use," he said. "The set still doesn't work. See
- Dial Light is the only one doing a blessed thing."
When he returned, Volt's steps were dragging. "Nothing happened,
eh? I thought so, when I didn't hear any noise. Guess this fellow
was telling the truth at that." Volt was thoroughly dejected.
But Sleuth wasn't discouraged. " A thing like that can happen
in the best of circuits," he said kindly. "We'll just have to look
a little further."
(To be Continued.)
Posted 2/ 16/ 2011