August 1955 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
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
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 his
"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 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."
"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," 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."
"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."
"Wait up!" Carl commanded. "What's this jive about widening the frequency response?"
"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!"
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 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."
"Well, 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
"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 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."
Carl & Jerry: Their Complete Adventures is now available. "From
1954 through 1964, Popular Electronics published 119 adventures of Carl Anderson and Jerry Bishop, two teen boys with
a passion for electronics and a knack for getting into and out of trouble with haywire lash-ups 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
- Pi in
the Sky and Big Twist, February 1964
Bell Bull Session, December 1961
Cow-Cow Boogie, August 1958
Picture, June 1955
- Electronic Eraser,
- 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,
- 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,
Santa's Little Helpers - December 1955
Two Tough Customers - June 1960
Transistor Pocket Radio, TV Receivers and Yagi Antennas, May 1955
Stomping, March 1962
- 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,
- "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 December 6, 2019(original 3/6/2014)