sounds about as serious as 'Wonkavision,' but unlike the candy maker's
fictional machine that transported chocolate bars across the room, Stratovision
was in fact a serious proposal. It was an early form of satellite television.
Since orbiting communications satellites would not be practical for
another decade, Westinghouse devised a system in 1945 using aircraft
flying at high altitude to relay television signals. Engineers calculated
that 14 airplanes circling at 25,000 feet could provide coverage to
78% of the country. By 1950 they had a working system, but needless
to say (because nobody has ever heard of it... except you, now), the
concept ultimately did not pan out. It was not because the system failed
to work as designed, but because there was not enough demand for coast-to-coast
broadcasts at the time. Thanks to Terry
W. for providing this article.
Is Stratovision the Answer?
By Kenneth Boord
The experimental Stratovision station (a modified B-29). flying
at 25,000 feet over the Pittsburgh area, rebroadcast telecast
picked up from the east coast television network over an estimated
area 525 miles in diameter. Programs from the ground stations
are picked up on the antenna projecting above the tail. and
rebroadcast from the long. mast-like antenna extending down
from the nose of the plane.
Fourteen planes would provide adequate coverage for approximately 78%
of the people in the U.S.A.
Although Stratovision experiments
in the United States have been suspended temporarily, there are many
TV authorities who believe it is the only answer to truly adequate "nationwide"
video coverage - including the small towns and rural areas as well as
the large metropolitan centers of the country. Five years ago (1945),
the Westinghouse Electric Corporation, in cooperation with The Glenn
L. Martin Co.) announced the intention of developing this system in
the United States. What is Stratovision?
It is airborne television-transmission relay from planes in
motion at high altitudes. By raising the broadcasting antenna to greater
heights, relatively large improvements in v.h.f. (very-high frequency)
and u.h.f. (ultra-high frequency) transmission range may be obtained.
"Radio" horizon distances, of course, are largely dependent upon atmospheric
conditions. A transmitting antenna 30,000 feet above the earth's surface
has a "line of sight" distance to the horizon of 211 miles, and this
distance roughly represents the service area of such a v.h.f. or u.h.f,
transmitting antenna. Assuming true spherical earth conditions, calculations
indicate that television coverage over this large distance is attainable
with powers equivalent to those used in present-day commercial television
A transmitter operating at 600 megacycles, airborne
30,000 feet above the surface of the earth, with an effective radiated
power of 25 kw. assumed, will achieve a field intensity of 2 millivolts
per meter for a 3D-foot high receiving antenna, out to 238 miles. This
distance represents the coverage from an airborne station over the earth.
Minimum values of field intensity occur at several points closer
to the transmitter and fall below the value of two mv/m. required for
service. These minimums will not occur at the same distances for a different
receiving antenna height. This makes it possible to increase the field
intensity at any location by changing (either raising or lowering) the
receiving antenna by a few feet. Energy at the receiving antenna arrives
from the transmitting antenna over two paths - a direct path and a reflected
path. Thus, the net energy at the receiving antenna is a vectorial addition
of these two components. As the distance between transmitter and receiver
is changed (or the antenna heights are changed), the changing vectorial
relationship produces nulls and maximums. There are as many nulls between
the transmitter and its horizon as the number of half-wavelengths that
the receiving antenna is above ground. It is desirable to reduce the
receiving antenna height as the receiver is moved closer to the transmitter,
even to the point of laying it close to the ground when the location
is near the transmitter.
Naturally, terrain factors influence
the coverage obtained, and these factors have a greater attenuative
effect in the u.h.f. television band than in the v.h.f. band.
The Westinghouse and Glenn Martin
companies undertook two series of flight tests to study the propagation
and plane motion effects. The first of these studies was made with a
twin-engine PV-2 aircraft, capable of operation at 25,000 feet. (This
ship was by no means of the type suitable for day-to-day broadcasting
but was quite suitable for propagation measurements.)
were installed in the unpressurized cabin of this ship. A 250-watt transmitter,
operating on 107.5 mc., and a 5 kw. (peak of pulse) transmitter operating
at 514 mc., were flown at various altitudes away from Baltimore (Maryland),
and continuous recordings of field intensity were made at locations
ranging from Norfolk (Virginia), to Pittsburgh (Pennsylvania), and Boston
During the one-year flight-test period using
PV-2, measured field intensities were compared with calculated values
and effects of motion of the plane upon the pulsed waveform of the 500
mc. transmitter were studied. No effects of the motion of the plane
were found except for the expected variation of field intensity as the
distance changed. Measured field intensities agreed with calculated
values reasonably well when the receiving antenna site approached a
true spherical earth condition. Departure below predicted values was
noted when the receiving antenna was down behind a hill. In a comparison
study of measured and calculated values when the receiving antenna was
set up on a beach at Norfolk (Virginia) - the total path between transmitter
and receiver being over the waters of Chesapeake Bay - it was noted
that even with this ideal "spherical earth" location, the minimums were
never as deep as calculated.
As a result of these tests, the
two companies were encouraged to equip a .more suitable plane for actual
picture transmission in accordance with commercial television standards.
A complete set of modern TV transmission equipment was built
and installed in a B-29 "Super Fortress" with all military armament
removed to make room for the TV equipment. This aircraft is a pressurized,
four-engine, high-altitude airplane capable of operation at 30,000 feet.
1 C. E. Nobles, originator of the Stratovision
system for airborne television and frequency modulation transmission,
monitors the television signal received and transmitted from the Stratovision
airplane. Ben Carroll (shown at right), Martin Stratovision project
engineer, listens at the sound monitoring position.
2 C. E.
Nobles at the twin video monitoring boards in the experimental Stratovision
airplane. The boards are so arranged that each can be used separately
to monitor the video signal coming to the plane or the signal being
transmitted by the plane, or they may be used together so that the signal
picked up by the plane appears on one screen while the plane's broadcasted
video signal is monitored on the other. The TV picture is viewed on
the large screen.
3 Angus A. Macdonald and Larry Smith, Westinghouse
engineers, record current and voltage readings of the 1000 watt transmitter
used to rebroadcast frequency modulation sound signals from the airplane.
This transmitter plus the TV transmitter and the other equipment aboard
the plane generated so much heat in early flight tests that a refrigeration
system, capable of air conditioning a seven room house, was installed
Television equipment installed in this
ship consisted of receivers capable of receiving standard commercial
television stations or a special 547.5 mc. relay link from the Westinghouse
studios in Baltimore (Maryland). Transmitting equipment capable of emitting
5 kw. of video and 1 kw. of sound on TV Channel 6 (82-88 mc.) and monitoring
and control equipment were also installed. In addition, other transmitters
operating on 250 mc. (with 200 watts c.w.) 750 mc: (with 200 watts c.w.),
and 3300 mc. (with 50 kw. peak of pulse) were installed to carry out
further propagation measurements.
Receiving circular dipoles
were located on an eight-foot streamlined mast atop the vertical tail
fin. These antennas were used to receive standard ground stations for
rebroadcast. The vertical tail fin was chosen as a location for the
receiving array because it was the spot most isolated from the transmitting
array, thereby reducing the problems of receiving weak signals in close
proximity with the 5 kw. video and the sound transmitters. This location
plus the use of filters made it possible to receive any commercial channel
except Channel 5, where the lower sideband components of the Channel
6 transmitter were relatively high.
In broadcasting position,
the main transmitting antenna mast hung vertically downwards. This mast
carried a two-element turnstile array for the Channel 6 video carrier,
a single-element circular dipole sound antenna, and a 547.5 mc. relay
link receiving array. The mast is 28 feet long and induced some 600
h.p. of additional drag to the plane in spite of its being streamlined.
This array, of course, was retractable for take-offs and landings.
for all equipment was obtained from three 15 kva., 500-cycle alternators
coupled directly to the plane's engines. The plane used a 70,000 BTU-per-hour
air conditioning system in order to dissipate the heat from the operating
compartment. Without air conditioning, the compartment temperatures
reached 134 degrees Fahrenheit in spite of the fact that outside air
temperatures were 25 degrees Fahrenheit.
This equipment was
flown more or less regularly from June of 1948 to February of 1949.
Usual flight procedure after take-off from Baltimore (Maryland) was
to climb to operating altitude at Baltimore. During the hour required
to climb, equipment was brought on the air and checked out. Upon reaching
altitude, the plane was flown away from Baltimore while continuous propagation
measurements and range measurements were being made. The programs of
WMAR-TV of Baltimore usually were broadcast on Channel 6.
each flight, many TV fans wrote in to describe results of the test at
their particular location. These reports from the public were numerous;
several hundred letters were received on some flights and proved to
be a valuable source of information. Area covered by reports agreed
very well with predicted coverage.
An angle of five degrees
or greater is obtained for only the first mile from a 500-foot high
antenna compared with 64 miles from the 30,000-foot antenna. An angle
of one degree or greater is obtained for only 5 miles from a 500-foot
high antenna as compared with 168 miles from the 30,000-foot antenna.
Stratovision proponents estimate that it would require only
eight planes in "relay" to provide a transcontinental network and six
additional planes to give adequate coverage to 78 percent of the 149,000,000
people in the United States.
As to the future of airborne TV,
C. E. Nobles, head of Stratovision work for Westinghouse, says "The
major technical problems of the system have been solved, and the commercial
development awaits only the crystallization of public demand for the
expanded services offered by airborne broadcasting, application of the
system by the radio industry to meet this demand, and the clarification
of channel facilities available to make possible this application."