Who Killed the Signal?
1943 QST Article
this amazing electronics allegory was written by then-QST-editor Clinton
B. De Soto!
February 1943 QST
of Contents]These 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 (if any) are hereby acknowledged.
See all available
Who Killed the Signal?
A Radio Mystery Serial
By Clinton B. De
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.
But radio 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
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 was dead.
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 better still).
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."
Most 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 ensembles.
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
One thing 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,"
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.
It's 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
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.
"Might 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
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 confidentially.
"Can you tell us anything more?" Sleuth asked.
"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?"
"That's 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
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
"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
"All right then? You've been talking about it enough."
"I'll explain 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
"Hmmph." Volt Meter seemed out of his element,
but Milly's response could be read on her face.
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
"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."
" Tell us about a.c.," Sleuth
"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.
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!"
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
"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."
was silence for a moment. Then a speculative look came over Volt Meter's
face. Suddenly he jumped up.
"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
"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."
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
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
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
(To be Continued.)
Posted 2/ 16/ 2011