July 1967 Radio-Electronics
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
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With as much ink as was
used in reporting on this "Major Antenna Breakthrough?" item in the July 1967
issue of Radio-Electronics magazine, it could have qualified as a
feature story. The breakthrough is an active antenna, dubbed a Subminiature
Integrated Antenna (SIA), with amplifying transistors in series with the radial
elements. This hookup makes practical, it is claimed, to reduce antenna length
from 1/4 to 1/50 wavelength and still have reasonable signal pickup. A TV or FM
receiver version could be 2 or 3 inches long. Half a year later the magazine had
an SIA article entitled "Build a Mini-Tenna,"
which operated in the 88-108 MHz FM radio band. There does not seem to have been
a widespread adoption of active antennas for most applications; however, they
are found today significantly in GPS units and the satellite radio antennas on
top of your vehicle. At this point, they are useful mostly for receivers due to
power handling limitations.
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News Briefs
Major Antenna Breakthrough?
Ever since Marconi stretched a longwire and copied history's first DX, the problem
of antenna size versus available space has given engineers and technicians headaches.
An antenna which is physically small (compared to wavelength) simply doesn't capture
very much signal. Hence its gain is low and it doesn't respond very well to weak
signals. For convenience, however, most people prefer small antennas; TV rabbit
ears are a good example. Yet such antennas are inefficient.
Three recent developments could mean a really efficient yet small antenna. Putting
an rf preamp at the antenna terminals has been done for some time for a greatly
improved signal/noise ratio. But the relatively recent development of inexpensive
high-gain rf transistors has made possible a type of antenna which is a combination
of active and passive elements. The idea they seem to share is to "marry" transistors
to individual antenna elements.
Late in April the US Air Force revealed what was called a Subminiature Integrated
Antenna (SIA). As shown in the drawing, transistors are connected between the antenna
elements and the coaxial lead-in. A top hat of capacitance is also connected to
a common junction. This hookup makes it practical, it is claimed, to reduce antenna
length from 1/4 to 1/50 wavelength and still have reasonable signal pickup. A TV
or FM receiver version could be 2 or 3 inches long. Because of the transistor's
beta, the SIA has a lower resonant frequency than a passive element alone. Characteristic
impedance is close to that of standard coaxial cables, and can be matched by adjusting
the transistor transconductance. Bandwidth of the solid-state antenna is greater
than that of a passive version. The new antenna can be made in horizontal or vertical
configurations, bidirectional or omni-directional.
SIA was developed during a 4-year program by the Air Force. Inventor is Edwin
M. Turner of the Air Force Avionics Lab, Wright-Patterson Air Force Base, Dayton,
Ohio. He estimates an SIA for TV reception could be about the size of a penlight
battery, and could be manufactured for $2 to $3.
An antenna that seems similar was demonstrated at the October 1966 convention
of the Audio Engineering Society in New York City. Described as an "omnipolar high-gain
vertically polarized antenna of small dimension" it appeared to be a plastic tube
about 14 inches long and 1 inch in diameter. Its developer - William S. Halstead,
of Multiplex Development Corp. - said that inside the tube was a spiral of wire
which formed a monopole antenna element. At the base of the tube (shown at the right
in the photo) Halstead stated there was an FET preamp driving the coax back to the
receiver.
The Halstead antenna was devised for mobile reception of SCA subchannels from
FM stations. It was claimed to have a gain of 4 dB over a reference dipole, with
equal response to both horizontally and vertically polarized transmissions. It has
maximum response when in a vertical position, and minimum when 45° away from
vertical.
In January 1967 the antenna was placed in service on the Eastern Air Lines Air
Shuttle run between Washington, New York and Boston. It became part of a system
operated by Newsrad, Inc., which furnishes news and weather reports to airline passengers.
Tape cartridges containing the newscasts are played in the studios of New York's
WOR-FM and transmitted via their SCA subchannel. Signals are then picked up by the
Halstead antenna and the Newsrad receiver in a plane just before it lands at LaGuardia
Airport in New York City.
In September 1966 several demonstrations of a new antenna were held in the small
Ohio town of Lewisburg (near Dayton). The antenna- known as the Americus SkyProbe
- was developed by John M. Eagle of UniScience Laboratories, Inc. at Lewisburg.
As shown in the photo, the antenna is built inside a plastic tube. In one demonstration,
it was connected to a TV receiver with 300-ohm twin-lead and then dropped into the
bottom of a metal water well 139 feet deep. Observers reported good reception of
vhf TV stations 20 miles away, and fair reception of vhf stations 50 miles away
and a uhf station at 20 miles.
Eagle states that his antenna is "not a diapole" [sic], but can receive both
color and uhf beneath the earth's surface. He claims that classic theories of TV
and radar reception are "incorrect or incomplete"; that the earth's magnetic field
carries "video and audio"; and that neither antenna size nor height is a "controlling
factor" in reception.
The SkyProbe antenna has been advertised and sold in stores in Ohio. Ads claim
it is solid-state, but no further details were available from UniScience.
None of the above cases have shown protection from multipath or ghosting. Each
seems to use semiconductor gain to compensate for antenna inefficiency.
Time Signals
Standard frequency and time stations WWV (Fort Collins, Colo.) and WWVH (Maui,
Hawaii) are now making voice announcements in Greenwich Mean Time (also known as
Universal Time, or UT). The National Bureau of Standards stations thus have joined
time and frequency stations in other countries which have been making announcements
in GMT for some time.
Low-frequency WWVB (which does not make time announcements in voice) is one of
only two stations currently transmitting the internationally recognized unit of
time - the atomic second - in a coordinated system. DCF77, at Mainflingen, West
Germany, transmits pulses which are synchronized to within 1 msec of those from
WWVB. Both stations use the Stepped Atomic Time System; time pulses are one atomic
second apart, and carrier frequencies remain constant at their nominal values.
More on Walkie-Talkie Rule Change
As reported in this column in our April 1967 issue, the Federal Communications
Commission has proposed to change its regulations governing 100-mW Part 15 transmitters
operating in the 27-MHz Citizens band. Chief provision is to move license-free walkie-talkie
operation to 5 channels in a band from 49.9 to 50.0 MHz.
If adopted, the new rules would also require the following: frequency tolerance
of 0.01 %; total dc power input under any modulation condition not to exceed 100
mW; superregenerative detector in associated receiver prohibited; transmitter must
be type approved; certain limitations on spurious emissions.
Present 100-m W operation in the 27-MHz band would be permitted for 7 years following
adoption of the new regulations.
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