August 1955 Popular Electronics
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
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In this episode of Carl & Jerry, the teens ponder a question
posed by Jerry's mother upon looking down their hillside home: "[L]ook
at all those TV antennas down there. Hardly two of them are alike;
yet they're all intended to receive the same stations. How come
there are so many different kinds?" That was all the pair needed
to set them off in an investigation to determine the answer. Being
avid electronics and RF hobbyists and experimenters, they discuss
the principles of how antennas work, various types of transmission
lines, impedance matching, antenna types, bandwidth, and other topics
relevant to the challenge. As with most Carl & Jerry stories,
the intent is to educate the reader. As a bonus, I posted two of
the electronics-related comic panels that were in this edition of
Carl & Jerry: TV Antennas
By John T. Frye
The two boys climb a hill, then talk about kinds of TV antennas
and how they work
The hot August sun beat down on the two boys climbing up the
steep path. Lanky, athletic Carl Anderson scarcely breathed hard
as he forged steadily up the hill; but behind him his overly plump
chum, Jerry Bishop, puffed like a steam locomotive as he toiled
along the steep ascent. In spite of his noisy effort, Jerry kept
falling farther and farther behind, and finally he came to a full
stop and collapsed in the shade of a huge boulder beside the path.
"How come you're dropping anchor there, Blimp Boy?" Carl called
down. "We've still got a quarter of a mile to go to the top."
"I can never make it," Jerry gasped feebly. "Go on without
me. Just say my spirit was willing but the flesh was weak. Leave
me a dozen sandwiches or so to make my last moments comfortable."
"Not a chance!" Carl interrupted harshly. "I coaxed you on this
hike to sweat some of the fat off you, and off it comes - one way
or another. We agreed to eat, you will remember, when we got to
the top of the hill. Well, if I've got to go on by myself. I'm going
to take the lunch with me and eat it - all of it - up there just
as we planned."
"You wouldn't dare!" Jerry cried, with the quick instinctive
anger of a hungry dog who sees his bone suddenly snatched from him.
"Oh no?" Carl said tauntingly, as he squatted on his heels
and opened the lunch basket he was carrying. Very deliberately,
he removed a thick paper-wrapped sandwich . and slowly pulled out
the toothpick thrust through it.
With a snarl of mixed hunger
and rage, Jerry leaped to his feet and charged up the path toward
his tormenter. Carl barely had time to toss the sandwich back into
the hamper and scramble upward out of Jerry's clawing reach. The
latter was so incensed by the horrifying prospect of Carl's eating
all the lunch that he did not slacken his pace and the two boys
arrived at the top almost neck and neck.
"You made it!"
Carl congratulated, as he flung himself at full length on the thick
grass beneath a tree.
For a minute, Jerry stood over him
with his face still wearing its menacing scowl, but then as he looked
about and realized he had actually reached the summit, his round
countenance broke into a pleased grin and he sat down abruptly beside
"We better cool off a little before we eat,"
Carl suggested. "It certainly is a wonderful view, isn't it?"
"It sure is," Jerry agreed, with his head buried in the
picnic hamper. "Now that we've cooled off for at least a couple
of hundred seconds. let's eat. Do you want your tenderloin sandwich
with or without .mustard?"
There was little conversation
for the next few minutes as the boys waded through the assorted
sandwiches, hard-boiled eggs, and fresh fruit that Carl's mother
had provided. Finally, though, when they were munching their chocolate
bar dessert, Carl said lazily:
"Jer, look at all those TV
antennas down there. Hardly two of them are alike; yet they're all
intended to receive the same stations. How come there are so many
Jerry pillowed his head on his clasped
hands and stared up at the fleecy white clouds drifting across the
blue sky overhead. "To answer that properly really takes a lot of
doing," he said slowly. "You almost have to go into the subject
of how TV antennas work."
"So let's go into it," Carl promptly
"I've got the time, and you think you've got the
"When TV broadcasting first started," Jerry
began, "the receivers were invariably close to the transmitter,
and the engineers simply adapted the old standby short-wave receiving
antenna, the half-wave dipole. This is simply a conductor which
is an electrical half-wavelength long at the frequency being received
and which is cut in two at the middle so that each half feeds into
one part of a two-conductor feedline, such as a twisted pair, coaxial
cable, or piece of twin-lead. In radio work, the conductor is usually
wire; but since a half wave is only a matter of a few feet on the
TV frequencies, the TV antenna was made up of a couple of pieces
of aluminum tubing secured to a center block of insulation."
"I don't see anything like that down there," Carl remarked as
he raised himself on an elbow and looked down at the rooftop antennas.
"No, that simple antenna didn't last long because it had several
serious faults. For one thing, it had a front-to-back ratio of 1
to 1. By that I mean its horizontal reception pattern looked like
a figure '8.' While practically no reception was had off either
end of the dipole, identical reception lobes extended out from either
side. If you called one side the 'front' of the antenna and pointed
it at a station, another station at the rear would be equally favored
in reception. As more and more stations came on the air, forcing
many to share the same channel, this became a serious defect. Secondly,
the output impedance of the dipole is about 72 ohms, an inconvenient
value for matching to low-cost, low-loss transmission lines."
"I don't dig this impedance-matching business as well as I might,"
"Every piece of equipment that generates, carries, or receives
r.f. currents has a certain amount of built-in opposition to the
flow of those currents that is called 'impedance,' " Jerry explained,
beginning to enjoy his role of lecturer. "In order to transfer the
maximum amount of power or signal from one piece of equipment to
another, their respective impedances must be equal or 'matched.'
If the TV antenna is not matched to the feedline and if the feedline
is not matched to the receiver, you not only lose a lot of signal
but the mismatch is likely to generate annoying ghosts in the picture.
Most TV sets are built with an antenna input impedance of 300 ohms.
Low cost and efficient twin-lead designed to match this also has
a 'surge' impedance, as it is called, of 300 ohms. But if you have
to feed a 72-ohm half-wave dipole antenna into the end of this 300-ohm
feedline, you have a 4 to 1 mismatch."
"And I guess a 52-ohm
coax line would be worse?"
"It can be done, and some receivers have a 52-ohm input for
this line, but it is much more expensive than twin-lead and has
a much higher loss than a good grade of dry twin-lead. It was easier
to change the dipole so that its impedance would match the inexpensive
300-ohm flat line."
"How did they cut that caper?"
"Just by placing another conductor a half wavelength long three
or four inches above the dipole and connecting its ends to the outside
ends of the dipole. This changed the simple dipole into a 'folded
dipole,' with several important advantages. For one thing, the antenna
impedance was quadrupled so that it was almost an exact match for
the 300-ohm line. Secondly, the frequency response of the folded
dipole is much wider than that of the simple dipole."
up!" Carl commanded. "What's this jive about widening the frequency
"The dipole delivered maximum received signal
strength only on the channel for which it was cut. Signals on adjacent
channels excited much less response in the antenna, and signals
from channels still farther removed from the antenna's resonant
frequency produced still less response. Since the antenna responded
only to signals close to its resonant frequency, we say it had a
narrow bandwidth. The folded dipole responds much more strongly
to signals on adjacent channels, so we say it has a wider bandwidth.
"Roger. With a wide-band antenna, you can receive
several channels on the same antenna. With a narrow-band job, you
can receive only one channel well."
"I do believe you're getting brighter!"
Jerry said sarcastically.
"At any rate, the folded dipole still did not have all the answers.
Especially, it did not prevent receiving a station just as well
off the back as the front. To correct this fault, TV design engineers
borrowed the Yagi antenna radio hams had been using on 10 and 20
meters for years. To change a folded dipole into a Yagi, you mount
the dipole horizontally on a long horizontal boom. On this boom,
parallel to the dipole, you mount several other metal rods or tubes
called 'parasitic elements' because they have no direct connection
to the 'driven element' that is connected to the feedline. Parasitic
elements on the front part of the boom are called 'directors,' and
they are a trifle shorter than the driven element and must be mounted
at certain critical distances ahead of that element. At the rear
of the boom, also at a critical distance, is mounted a parasitic
element called a 'reflector' that is somewhat longer than the driven
"A complete Yagi may have all the way from 3 to 12 or more elements.
Directors concentrate the received signal on the driven element
in much the same way that lenses focus light. The reflector reinforces
this action in the same manner that a polished surface will reflect
and concentrate light rays on a particular spot. The end result
is that the reception of a signal arriving from the front of the
antenna is greatly improved and response to a signal arriving from
any point of the compass except the front is cut way down."
"Sounds like the perfect answer to the TV antenna problem"
"For single-channel reception, it's hard to beat - but there's
the rub. In its conventional form, a Yagi is a very narrow-band
affair good for reception only of the single channel for which it
is designed. Lately, however, the engineers have given the old Yagi
a new look by working it over into what is known as the broadband
Yagi - capable of yielding good signal strength and excellent on
all 12 v.h.f. channels. This is done by using more than one driven
element and by carefully adjusting the length and spacing of the
parasitic elements so that they do double or triple duty, producing
effectively the equivalent of several different Yagi antennas mounted
on a single boom. That antenna over there, next to the church, which
is called an 'Interceptor,' is a good example of this design."
"How about those jobs with the elements sticking out every
which way? I think they are called conicals."
back to our original dipole, increasing the physical size of the
dipole elements will widen the frequency response. Theoretically,
the best way to do this is to use metal cones mounted tip-to-tip
for the elements. The cones can be flattened into triangular sheets
of metal without much loss of effectiveness, and this is actually
done on the u.h.f. channels. The resulting dipoles are called 'bow-ties'
because of their appearance, and are usually mounted in front of
a reflecting metal grid or inside the jaws of two such grids edge-connected
at a 90° angle to form what is known as a 'corner reflector.'
"On the v.h.f. channels, where wavelengths are measured
in feet instead of inches, a bow-tie of proper dimensions would
be too bulky and expensive and have too much wind resistance. However,
metal rods or tubes that preserve the outline of the bow-tie, and
that might be considered the skeleton of the original cones, serve
almost as well. By inclining the skeleton wings of this 'conical'
dipole slightly forward to form a shallow funnel, reception on the
higher channels is improved. TV signals are directed in toward the
feedline point in much the same way that sound waves are collected
by an old-fashioned hearing trumpet. A skeleton bow-tie reflector
is usually mounted behind the conical antenna to improve the front-to-back
ratio. To get still more strength in fringe areas, it is a common
practice to stack two, four, or even more of these conical 'bays,'
as they are called, one above the other on the same mast, and connect
them to a common feedline. To insure that the signals picked up
by the several bays actually reinforce instead of buck each other,
it's necessary that bays be mounted the proper distance apart and
that they be connected together with special 'stacking harness.'
"Any more TV antennas?" Carl asked drowsily.
"Lots more, but you'd never stay awake to hear about them," Jerry
observed tartly. "Some antenna manufacturers depend upon stacking
several dipole-and-reflector bays vertically for increased gain.
Half-wave elements, properly phased, may be mounted side by side
and several such bays stacked to form what is called a 'collinear
array.' The appearance of such an antenna, together with a reflecting
screen, has given rise to its popular nickname of 'the bedspring
antenna.' Other manufacturers combine Yagi and conical antennas
on a single boom, hoping to get the benefits of both from this marriage."
"What's meant by antenna gain?"
"That's the ratio between the signal voltage delivered by the
antenna to the feedline on a certain channel and the voltage delivered
by a reference dipole antenna cut to the frequency of that channel
and mounted in the same spot. This ratio is expressed in decibels.
For example, if the antenna under test delivers twice as much signal
voltage as does the dipole on Channel 6, we say it has a 6-db gain
on that channel. If it delivers four times the voltage, it has a
"What characteristics would you say the perfect
TV antenna should have?"
"First, it should have high gain;
second, it should maintain this gain across all v.h.f. and u.h.f.
channels with no peaks or dips; third, it should present a consistent
300-ohm impedance to the feedline on all frequencies; fourth, it
should have a single, narrow reception lobe and should present infinite
rejection to signals arriving from the side or rear; and finally,
it should be cheap, light, and easily mounted, with a low wind resistance
and a beautiful appearance."
"Sounds like quite an order."
"It is, especially when you realize that antenna gain, bandwidth,
front-to-back ratio, and impedance are all closely interlocked so
that you cannot vary one of them without changing all the others.
And right there you have your answer as to why there are so many
different kinds of antennas. Each manufacturer tries a different
compromise in his approach to this ideal antenna. One may stress
high maximum gain or front-to back ratio; another advertises price
and appearance; still another may boast that the response curve
of his antenna has no sharp dips and valleys in it - something especially
important in an antenna used for color TV reception. Each advertising
claim appeals to a certain group of customers who feel that the
stressed characteristic is just what they need to solve their reception
troubles. If it doesn't, then they are ready to try another new
antenna, always hoping they will eventually come across the perfect
TV antenna which will insure perfect reception all the time."
"You sound a little cynical about this." "I'm not really.
I know how important it is to have a good antenna, especially in
a weak-signal area; but I also know for a fact that the TV antenna
can only do so much. It cannot receive a signal that just isn't
there; nor can it compensate, beyond a certain point, for a poor
receiver. The TV antenna is like the automatic choke on a car; it
gets a lot of blame for 'sins' of which it is not guilty."
Carl rose and brushed the grass from the seat of his pants.
"Well, I guess we had better be starting for home, Marconi.
Do you think you will be able to totter down the hill or had I better
just roll you like a barrel?"
"Don't get smart with me,"
Jerry said, as he struggled to his feet, trying not to wince at
the protest from his sore muscles, "Just don't get in my way going
down as you did coming up."
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
- The Hand of Selene, November 1960
Feedback, May 1956
Abetting or Not?, October 1956
Electronic Beach Buggy, September
- Extra Sensory Perception,
- Trapped in a Chimney, January
- Command Performance, November 1958
- Extracurricular Education, July 1963
- 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 March 6, 2014