August 1955 Popular Electronics
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
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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 Popular Electronics.
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
"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
"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
"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.
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
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 his friend.
"We better cool off a little before
we eat," Carl suggested. "It certainly is a wonderful view,
"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
"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 different kinds?"
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
"So let's go into it," Carl promptly urged.
"I've got the time, and you think you've got the information."
"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."
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," Carl admitted.
"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."
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. Catch?"
"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!"
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 element.
"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."
going 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 12-db gain."
"What characteristics would you say the perfect TV antenna
"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."
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
- Electronic Trap, March
- Geniuses at Work, June
- Eeeeelectricity!, November
- Anchors Aweigh, July
- Bosco Has His Day,
- The Hand of Selene,
- Feedback, May 1956
- Abetting or Not?, October
- Electronic Beach
Buggy, September 1956
- Extra Sensory
Perception, December 1956
- Trapped in a Chimney,
- Command Performance,
Education, July 1963
- Treachery of Judas, July
- The Sucker, May 1963
- Stereotaped New
Year, January 1963
- The Snow Machine, December
Education, July 1963
- Slow Motion for
Quick Action, April 1963
- Sonar Sleuthing, August
- TV Antennas, August 1955
- Succoring a Soroban,
- "All's Fair --", September
- Operation Worm Warming,
- The Blubber Banisher,
- The Sparkling Light, May
- Pure Research Rewarded,
- A Hot Idea, March 1960
- The Hot Dog Case, December
- A New Company is Launched,
- Under the Mistletoe,
- Electronic Eraser,
- Blubber Banisher, July
- "BBI", May 1959
- Ultrasonic Sound Waves,
- The River Sniffer, July
- Ham Radio, April 1955
- El Torero Electronico,
- Wired Wireless, January
- Electronic Shadow,
- Elementary Induction,
- He Went That-a-Way,
- Electronic Detective,
- Aiding an Instinct,
- Two Detectors, February
- Tussle with a Tachometer,
- Therry and the Pirates,
- The Crazy Clock Caper,
Posted March 6, 2014