March 1972 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Unless you happened to live close
to a television broadcasting tower, receiving an acceptable signal has always been a matter
of luck. Obstructions such as buildings and terrain can greatly attenuate signal strength
and multipath can generate telltale ghost images and confuse the synchronization portions
of signals. It was bad enough with black and white (B&W) broadcasts, but the advent of
color made the situation notably worse because more information needed to be received properly
in order to display a good picture. Color TV adoption really began to take off in the late
1960s, and that is about the same time when electronics and technology magazines started publishing
articles like this one about how to select a roof-mounted TV antenna. A follow-up article
appeared in the April 1973
issue of Popular Electronics. The
December 1958 issue
had an antenna selection article as well, obviously for B&W TVs.
Complete listing of recommended antennas for your viewing area
By Forest H. Belt
Not too long ago, the only people who tried to convince
color-TV owners to buy rooftop antennas were the manufacturers of rooftop antennas. Today,
any TV salesman who assures you of a prime picture with only the set's rabbit ears - well,
he may disappoint you. Service technicians know; they get many requests to fix a color-TV
when the only problem is a weak or ghosty signal.
So don't disdain the antenna ads. Still, for the sake of snow-free and color-true viewing,
you should know what the ads try to say. Some play a numbers game, citing how many decibels
(dB) of gain (sensitivity) one antenna has over another. Some ads tell of "front-to-back ratio,"
others of "side lobes" or some other equally technical term. Catchy names abound, too: "Color
Brite," "Color Guard," "Color Spectrum," "Color Tuned," "Magic Color," "Sensar," "Stellar
2001," and so on.
Fig. 1 - Winegard uhf section fits in front of other companies' vhf units.
Fig. 2 - This antenna from Finco uses their frequency dependent principle.
The important matter is what kind of picture the antenna puts on the screen of your color
receiver. That may depend on where you live. How far away are the stations you watch? How
powerful are they? Are they vhf or uhf? How high can you have your outdoor antenna?
The accompanying full-page chart can guide your choice. Obviously, if you don't watch any
uhf stations, a vhf antenna is enough. Or, in a uhf-only area, you certainly have no use for
a vhf antenna. That is, you don't unless there's a not-too-distant vhf station you can pick
up with a high, sensitive antenna. In that case you might consider a powerful all-channel
model. And, if you're in a vhf-only or uhf-only locality, ask around - a new station starting
up soon might outmode your antenna.
Local, strong signals are usually received up to about 15 or 20 miles from the transmitting
antenna; medium signals up to 30 or 50 miles; and fringe signals out to 70 or 100 miles. Vhf
signals usually reach out somewhat farther than do uhf signals. Terrain modifies the TV signal.
If you find hills between you and the station, consider a more sensitive antenna (from the
next farther grouping). Likewise, if you live near the "far" end of a mileage grouping, you
may prefer the stronger antenna even if the countryside is only mildly rolling. Beyond the
mileages given above, even the best antenna brings in only a snowy picture - unless the terrain
is very flat or you can put the antenna extremely high.
The chart lists the models suggested by major manufacturers for each signal category. Don't
go only by price. Ask your dealer or distributor to show you the antenna you think best suits
your requirements. Judge its sturdiness. Is it simple to put together and raise into position?
Check its weatherproofing. Consider directionality and sensitivity (dB of gain). And, only
then, compare prices.
Several popular antenna models are shown on these pages. Some have odd shapes; but don't
think those shapes are accidental. They are carefully thought out, for very special reasons.
For All Channels. One example is a uhf design (Fig. 1) patented by Winegard.
What appears to be a folded dipole wrapped around the boom forms the only active element.
The lead-in is fastened to the opening at the bottom. There's another gap at the top of the
dipole - unlike ordinary folded dipoles which are solid along the side opposite the feed-line.
Two phasing bars (you can see only one in the illustration), connected to the top gap, are
just long enough at uhf to act like zero impedance (a short circuit) across the gap.
This peculiarity permits tacking the whole uhf array, which Winegard calls a "tetrapole
collector," onto the front of a vhf antenna and using a single downlead. At vhf, the phasing
bars and the uhf dipole have no resonance. They act as mere conductors tying the vhf antenna
to the block where the lead-in fastens. Far station signals in either uhf or vhf, the lead-in
"sees" 300 ohms impedance.
Element Shapes and Spacing. Another patented design principle applies to the Finco (Finney
Co.) antenna in Fig. 2. The company tags the idea its "frequency-dependent principle" (FDP).
Short elements, the ones that pick up high-numbered channels, are spaced far apart toward
the front of the boom. This trick imparts higher gain as the frequency goes up, which makes
up for natural losses in the TV spectrum.
Fig. 3 - Log-periodic antenna by JFD.
Fig. 4 - Element lengths follow exponential formula in GC Audiotex design.
Another special feature narrows the front lobe of this antenna. Dipoles are not straight
across. Instead, they are staggered along two electrically separate booms. Half of any given
dipole is on one boom; its other half is further along on the other. In effect, this transposes
the phasing of the feed centers from dipole to dipole. The twin lead-in connects directly
to the ends of the two booms.
A design called the "delta reflector" adds a third feature to Finco's antenna. Staggered
mounting of elements continues on the delta-shaped boom that connects at the back of the double
boom. The delta array forms a closed resonant loop to smooth response across the entire vhf
band. The delta reflector is said to block out signals from the rear more effectively than
a straight reflector, improving the front-to-back ratio.
Take a close look at the reflector elements up front, too. They are not solid. Insulators
divide them, to aid electrical breakup of longer elements so high-band vhf "cells" form. The
object, of course, is to improve performance on channels 7-12, which is poor in some TV antennas.
Ordinary spacing, called "yagi spacing," places elements the same distance apart along
the antenna boom. Gavin sells antennas of this design. Element lengths vary across the low
vhf band, to spread the gain. As usual, the long elements operate in thirds for high-band
vhf. Responses off the sides, called "side lobes," necessitate a slight forward-sweeping of
reflectors - which also strengthens the front lobe and raises gain. Short directors aid high-band
Editor's Note: Over the past year, with only a few exceptions, outdoor TV antennas have
not changed much. However, the selection of an antenna, especially for color TV, is important
enough that we decided to update a chart of recommended antennas which appeared almost a year
ago in Electronics World. Major differences include new model numbers and some price changes.
The Log-Periodic Idea. One design formula expresses a logarithmic relationship
between the velocity of TV signals and the size and spacing of antenna elements. JFD Electronics
pioneered this "log-periodic" principle. Gain goes up as frequency rises, and impedance across
the low and high spectrum stays smooth.
An all-channel log-periodic model is pictured in Fig. 3. Twin booms with alternating half-dipoles
accomplish feed transposition as already described, but the halves of each dipole are directly
opposite each other. Several forward elements incorporate insulators. However, the JFD insulators
are capacitive to "tune" the elements for high-band resonance.
Note that uhf array up front. Each set of flat dipoles
(there are two, mounted in wedge formation) is stamped from one metal plate. Spacing and lengths
of the dipoles follow the log-periodic formula, in the uhf band. The tapered configuration,
both vertical and horizontal, captures uhf signals efficiently. Farther up front, the half-discs
are broadband directors. JFD calculates they deliver twice the gain of linear directors.
GC Electronics, under the Audiotex brand name, markets a line of antennas that follow a
different logarithmic formula. In Fig. 4, note the curved pattern outlined by the element
lengths. This special tapering, say designers, improves broadband response. The dipoles are
broken up by insulators, but not into thirds. The short outer stubs make a few of the driven
elements parasitic to others, smoothing gain across the bands. You can't see them plainly,
but small insulated wires transpose the feed between each successive pair of elements.
Interestingly, the uhf array sandwiches in between the main vhf array and some high-band
vhf directors up front. Insulators break those directors up into parasitic directors for the
uhf band. This antenna thus has multiple use of elements to develop higher gain at high band
vhf and at uhf, yet keeping overall response smooth.
Multi-Feature Type. Fig. 5 exemplifies a high-gain all-channel Jerrold
Electronics Corp. model called the "VU-Finder." Elements are spaced Yagi-style. Element lengths
get shorter linearly from back to front. The feed harness is transposed, but it is through
the unique disc-shaped boom insulators which have imbedded conductors. Every element is driven,
with shorter elements acting as directors for longer ones, and longer ones acting as reflectors
for shorter ones.
Fig. 5 - Jerrold uses circular insulators.
Parasitic elements that appear to be part of the uhf array boost high-band vhf gain too.
A specially shaped bow-tie in the middle of the front array is the only driven uhf element.
Jerrold named the patented design of the bow-tie an "extended resonance uhf dipole." The projections
at each corner are angle-aluminum. The bow-tie itself is not flat; it is molded with half-cylinder
depressions toward the sides.
Two V-angled booms carry the uhf parasitic elements, forming a corner reflector. To concentrate
the front lobe and boost gain even further, another boomful of parasitic directors extends
out in front of the bow-tie.
Indoor/Outdoor. Two unusual antennas are the JFD Stellar 2001 and the
Winegard Sensar. Both belong to a new breed of pre-amplified antennas designed for either
attic or rooftop installation.
Their amplifiers are solid-state and are part of the mast-mounted antenna. Coaxial cable
connects the antenna-and-amp unit to a power-supply distribution network at the set. The manufacturers
claim a performance radius of 40 to 70 miles, Keep in mind, though, that very broadband devices
such as these depend on fairly smooth terrain for any real distance.
Which brings up another point. Despite the need for a really good signal for acceptable
color reception, you just might be situated where the signal is good enough that you can get
by with an indoor antenna. Try it, but don't be disappointed if the unit that gives you a
near-perfect black-and-white picture still doesn't "cut it" for color.
Gavin makes an indoor model with two uhf loops, one slightly smaller for high uhf channels.
Some models have knobs to tune and orient the elements for ghost-free reception. You may have
to retune for each station.
JFD makes a complex indoor antenna. You can switch the elements as well as move them around
for various ghost conditions. The dipoles telescope, too, for best vhf reception, and an inductive-capacitive
circuit in the base lets you tune each station.
Channel Master sells an elaborate amplified indoor antenna called the "Chroma 1." The vhf
dipoles telescope, while the uhf element is a trapezoid-shaped wire loop, inside of which
is a small trapezoidal metal plate. A coaxial cable from the amplifier (in the base) feeds
the signal to an impedance-matching uhf/vhf splitter that connects to the TV set. Base controls
rotate the uhf antenna, switch from uhf to vhf, and tune the antenna-matching circuit for
best performance on each station.
You take the first step to dependable color-TV reception when you recognize the need for
a really good antenna. The second step is figuring out what antenna is "really good" for your
house. The third step is to buy and install the antenna of your choice.
Posted November 12, 2017