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. As time permits, I will
be glad to scan articles for you. All copyrights (if any) are hereby acknowledged.
Enjoy this amazing electronics allegory was written by then-QST-editor Clinton B. De Soto!
all available vintage QST articles
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.
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.
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,
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," 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
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 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
"Which do we tackle first, boss?" Volt Meter asked alertly, his pointer quivering with
"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 the chassis.
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 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 charge."
"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."
"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 current."
"Hmmph." Volt 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
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."
" Tell 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 persisted.
"I do," Power Cord answered firmly.
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
"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 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 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
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
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.
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