Misplaced Pages

#877122

58-541: Because the broadcasting antenna for Stratovision is usually hung beneath the aircraft in flight, it naturally has a great command of line-of-sight propagation . Although transmission distances are dependent upon atmospheric conditions, a transmitting antenna 30,000 feet (9.1 km) above the Earth's surface has a line of sight distance of approximately 211 miles (340 km). A Stratovision 25 kW transmitter operating from 30,000 feet (9.1 km) at 600 MHz will achieve

116-488: A Broadcasting magazine article, "Vietnam to get airborne TV: Two-channel service —one for Vietnamese, other for U.S. servicemen—starts this month", noted: Television broadcasting in South Vietnam ... begins January 21 and it's going to be done from the air. Two airplanes, circling 10,000 to 20,000 feet [3.0 to 6.1 kilometres] above the ground, will broadcast on two TV channels—one transmitting Saigon government programs;

174-749: A field intensity of 2 millivolts per meter for a 30-foot (9.1 m) high receiving antenna up to 238 miles (383 km) away from the aircraft. Stratovision tests were undertaken between June 1948 to February 1949. The first phase was undertaken by the Glenn L. Martin Co. and Westinghouse using a twin-engine PV-2 aircraft flying at 25,000 feet (7.6 km) that transmitted with 250 watts on 107.5 MHz and 5 kW on 514 MHz at Baltimore , Maryland so that recordings could be made at various locations ranging from Norfolk, Virginia to Pittsburgh , Pennsylvania and Boston , Massachusetts . The second phase of testing

232-402: A straight line . The rays or waves may be diffracted , refracted , reflected, or absorbed by the atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles. In contrast to line-of-sight propagation, at low frequency (below approximately 3  MHz ) due to diffraction , radio waves can travel as ground waves , which follow the contour of

290-511: A Stratovision service from the airfield of Purdue University . The effort began as a three-year experiment funded by the Ford Foundation . The program organized, produced and transmitted educational television programs four days a week from a DC-6AB aircraft flying at 23,000 feet (7,000 m) over the community of Montpelier in north central Indiana. MPATI delivered its programs to television channels 72 (call sign KS2XGA) and 76 (KS2XGD) in

348-418: A carbon image on an aluminum target plate or slide. The target plate is sequentially scanned with a focused beam of electrons, which were originally called cathode rays . When the electron beam strikes the carbon image areas, the carbon resists current flow, and the resulting lower electron current flow is adjusted to appear as video black. When the electron beam strikes the metallic-aluminum image areas, there

406-740: A collector. The Indian head was also used by the Canadian Broadcasting Corporation (CBC) in Canada in conjunction with its own monochrome test pattern, following the Canadian national anthem sign-off in the evening, and during its final years in the late-1970s and early-1980s it was shown before sign-on in the morning, after the showing of the SMPTE color bars . It was also used by Rhodesia Television (RTV) during British colonial times (varying between Northern and Southern Rhodesia ) following

464-691: A controversy with the Westinghouse company. During the Vietnam War, the United States Navy used Stratovision television technology when it flew Operation Blue Eagle from 1966 to 1972 over the Saigon area of South Vietnam . The television programs were aimed at two audiences on two channels: one was aimed at the general public and the other was intended for the information and entertainment of US troops who were stationed in South Vietnam. On January 3, 1966,

522-575: A direct visual fix cannot be made. Designs for microwave formerly used 4 ⁄ 3  Earth radius to compute clearances along the path. Although the frequencies used by mobile phones (cell phones) are in the line-of-sight range, they still function in cities. This is made possible by a combination of the following effects: The combination of all these effects makes the mobile phone propagation environment highly complex, with multipath effects and extensive Rayleigh fading . For mobile phone services, these problems are tackled using: A Faraday cage

580-540: A heavily modified Philips PM5544 test card. The Indian head was also used in Brazil by Rede Tupi , both as a test pattern and as part of a television ident , from its launch in 1950 until it became the first Brazilian television network to adopt colour television in 1971–72. The Indian head pattern was also used by Kuwait Television in Kuwait from its launch of television services in 1961 until it adopted colour television in

638-530: A high degree of consistency due to the device's simplicity. The monoscope tube is constructed similarly to a small cathode-ray tube (CRT), but instead of displaying an image, it scans a built-in image, producing a video signal. The tube has a perfectly proportioned copy of the test pattern master art (or a modified variant with the station ID replacing the Indian-head portrait, such as those used by KRLD-TV , WBAP-TV and WKY-TV ) inside, permanently deposited as

SECTION 10

#1732849111878

696-517: A radio signal from it, the propagation characteristic at these frequencies is called "line-of-sight". The farthest possible point of propagation is referred to as the "radio horizon". In practice, the propagation characteristics of these radio waves vary substantially depending on the exact frequency and the strength of the transmitted signal (a function of both the transmitter and the antenna characteristics). Broadcast FM radio, at comparatively low frequencies of around 100 MHz, are less affected by

754-481: A relief, which would transmit commercial television programs to Britain by Stratovision. Although these stories continued for some time, nothing became of the project. To date no pirate radio or television service has ever operated by means of Stratovision. The advent of fibre optic cable television systems and direct broadcast satellite services has supplanted Stratovision as a permanent means of television delivery. The Stratovision concept continues to be used as

812-472: A stop-gap measure where land-based transmitters are not possible and where large areas of territory need to be served with a television program. Line-of-sight propagation Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves can only travel in a direct visual path from the source to the receiver without obstacles. Electromagnetic transmission includes light emissions traveling in

870-484: A streamlined eight-foot (2.5 m) mast atop of the aircraft's vertical tail fin. The retractable 28 feet (8.5 m) long broadcasting antenna hung vertically beneath the aircraft. It was composed of a two-element turnstile array for video and a single-element circular dipole for sound transmissions. The receivers, transmitters and necessary air-conditioning were all powered by the plane's engines using three 15 kVA, 500 Hz alternators. Without air conditioning

928-497: A transcontinental network, and six additional planes to provide coverage to 78% of the United States. Charles Edward Nobles, the head of Stratovision for Westinghouse, said in his report: On September 30, 1954, Cuba used a DC-3 to broadcast a baseball championship game from the United States, the first live extracontinental broadcast. In 1961 a nonprofit organization, Midwest Program on Airborne Television Instruction , commenced

986-753: A variety of domestic power sources, and which had been airlifted to South Vietnam on December 28, 1965. They were to be put into community facilities around Saigon. AID was also spending $ 2.4 million to supply a total of 2,500 TV sets to South Vietnam. The entire project was under the control of Captain George C. Dixon, USN. He claimed to be installing AM, FM, shortwave and TV transmitters on the aircraft which would get their power from an onboard 100 kW diesel-fueled generator. The planes would not only relay programs from film chain kinescopes and video recorders, but they would also have live cameras to create their own live programs. Ground transmissions would be received from

1044-651: A videotaped production, followed by channel 11 at 8 p.m. with General Westmoreland introducing a two-hour program which incorporated one hour of the Grand Ole Opry filmed in Nashville, Tennessee . After that the Vietnamese channel would be seen for one and half hours a day and the U.S. channel for three hours daily. On 8 February 1966 The New York Times article "South Vietnamese Watch First TV Show" reported that South Vietnamese viewers had to strain their ears because

1102-453: Is a consequence of a circular segment of earth profile that blocks off long-distance communications. Since the vacuum line of sight passes at varying heights over the Earth, the propagating radio wave encounters slightly different propagation conditions over the path. Assuming a perfect sphere with no terrain irregularity, the distance to the horizon from a high altitude transmitter (i.e., line of sight) can readily be calculated. Let R be

1160-457: Is composed of a conductor that completely surrounds an area on all sides, top, and bottom. Electromagnetic radiation is blocked where the wavelength is longer than any gaps. For example, mobile telephone signals are blocked in windowless metal enclosures that approximate a Faraday cage, such as elevator cabins, and parts of trains, cars, and ships. The same problem can affect signals in buildings with extensive steel reinforcement. The radio horizon

1218-412: Is less resistance with higher current flow, and the resulting higher electron current flow is adjusted to appear as video white. This image was used to calibrate monitors in the station. Second, stations would use a cardboard-mounted lithograph of the test pattern (typically attached to a rolling easel in each TV studio); videographing the lithograph would create a second image that could be compared against

SECTION 20

#1732849111878

1276-433: Is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth. If the Earth were a perfect sphere without an atmosphere, the radio horizon would be a circle. The radio horizon of the transmitting and receiving antennas can be added together to increase the effective communication range. Radio wave propagation is affected by atmospheric conditions, ionospheric absorption , and

1334-454: Is usually chosen to be 4 ⁄ 3 . That means that the maximum service range increases by 15%. for h in metres and d in kilometres; or for h in feet and d in miles. But in stormy weather, k may decrease to cause fading in transmission. (In extreme cases k can be less than 1.) That is equivalent to a hypothetical decrease in Earth radius and an increase of Earth bulge. For example, in normal weather conditions,

1392-464: The Archie McPhee company, reminiscent of the times when a fairly common late-night experience was to fall asleep while watching the late movie, only to awaken to the characteristic sine wave tone accompanying the Indian-head test pattern on a black-and-white TV screen. The test card also featured in the opening sequence of the early 1960s science fiction anthology The Outer Limits . Nearly all of

1450-783: The Dominican Republic , the Indian-head pattern was used by its public broadcaster Corporación Estatal de Radio y Televisión (CERTV) in the late-1960s and 1970s (in conjunction with the EIA 1956 resolution chart test card) after playing the National Anthem of the Dominican Republic at sign-off. In Sweden , the Indian-head test pattern was used in test transmissions from the KTH Royal Institute of Technology in Stockholm alongside

1508-520: The 9 to 10 pm EDT time period. As part of the activity, a receiver was set up in a hall in Zanesville, Ohio , a small city on the outskirts of the broadcast area, to demonstrate to invited newspaper reporters that the system was capable of reaching "small town and farm homes". The tests were watched by many television viewers who sent in reception reports. From these reports it was calculated that Stratovision would require only eight relay planes to provide

1566-483: The Baseball World Series of October 1965 Stratovision had also been used to bring the games to the troops. The aircraft had picked up Voice of America radio broadcasts from California and relayed the signal to a ground broadcasting station. The Agency for International Development (AID) had purchased through the military Post Exchange Service , 1,000 monochrome, 23-inch television sets modified to operate on

1624-419: The Earth. This enables AM radio stations to transmit beyond the horizon. Additionally, frequencies in the shortwave bands between approximately 1 and 30 MHz, can be refracted back to Earth by the ionosphere , called skywave or "skip" propagation, thus giving radio transmissions in this range a potentially global reach. However, at frequencies above 30 MHz ( VHF and higher) and in lower levels of

1682-490: The Indian-head test pattern persists as a symbol of early television. Many U.S. television stations chose the image of the Indian-head card to be their final image broadcast when their analog signals signed off for the final time between February 17 and June 12, 2009, as part of the digital television transition in the United States . A variant of the card appeared on the Canadian sketch comedy show Second City Television in

1740-598: The NBC/CBS-derived "bullseye" patterns became the test card of choice. Since the 1990s, most television stations in the United States have broadcast continuously without regular sign-offs, instead running infomercials , networked overnight news shows, syndicated reruns, cartoons, or old movies; thus, the broadcast of test patterns has become mostly obsolete (though they are still used in post-production and broadcast facilities to check color and signal paths). Nevertheless,

1798-730: The RMA Resolution Chart 1946, Telefunken T05 test card, as well as other experimental test cards from Televerket and Chalmers University of Technology from 1948 until November 1958 when it was replaced by the Sveriges Radio TV (now Sveriges Television ) test card. In Australia, the Indian-head test pattern was used by TNT-9 in Northern Tasmania in conjunction with the Marconi Resolution Chart No. 1 from its launch in 1962 until it adopted colour television in

Stratovision - Misplaced Pages Continue

1856-530: The UHF band, by transmitting videotaped lectures from the aircraft to an estimated potential 5,000,000 students in 13,000 schools and colleges. The aircraft were equipped with two 2-inch (51 mm) videotape machines and two UHF transmitters. When MPATI signed on it used an "Indian head" test pattern card which was shown for five minutes before and between programs. The service ended in 1968 when it became embroiled in legal action over their application of Stratovision in

1914-521: The United States over a variety of television and radio frequencies. It has been used in several areas of operation, including Bosnia and Iraq . In 1969, news stories began to appear in the United Kingdom that Ronan O'Rahilly , the founder of the pirate radio ship based service called Radio Caroline , which at that time was not on the air, was about to launch Caroline Television instead. His plans called for two aircraft, one in service and one as

1972-478: The aircraft on TV sets tuned to channel 11 for Armed Forces Television, and channel 9 for programs in Vietnamese. On radio the broadcasts would be tuned to 1000 kHz for AM and 99.9 MHz for FM. On 7 February 1966, Broadcasting magazine reported that after working out a number of technical problems that the first show on channel 9 would begin at 7:30 p.m. and feature South Vietnamese Prime Minister Nguyen Cao Ky and U.S. Ambassador Henry Cabot Lodge in

2030-487: The atmosphere with height ( vertical pressure variation ) is to bend ( refract ) radio waves down towards the surface of the Earth. This results in an effective Earth radius , increased by a factor around 4 ⁄ 3 . This k -factor can change from its average value depending on weather. The previous vacuum distance analysis does not consider the effect of atmosphere on the propagation path of RF signals. In fact, RF signals do not propagate in straight lines: Because of

2088-405: The atmosphere, neither of these effects are significant. Thus, any obstruction between the transmitting antenna ( transmitter ) and the receiving antenna ( receiver ) will block the signal, just like the light that the eye may sense. Therefore, since the ability to visually see a transmitting antenna (disregarding the limitations of the eye's resolution) roughly corresponds to the ability to receive

2146-484: The hard-to-open, steel-shielded monoscope tubes were junked with their Indian-head test pattern target plates still inside, but many of the board-mounted lithographs survive. The master art for both the portrait and the pattern design was discovered in a dumpster by a wrecking crew worker as the old RCA factory in Harrison, New Jersey was being demolished in 1970. The worker kept the art for over 30 years before selling it to

2204-421: The height h is given in metres, and distance d in kilometres, If the height h is given in feet, and the distance d in statute miles, In the case, when there are two stations involve, e.g. a transmit station on ground with a station height h and a receive station in the air with a station height H , the line of sight distance can be calculated as follows: The usual effect of the declining pressure of

2262-446: The late-1970s, and another variant appeared on theatrical release posters for "Weird Al" Yankovic 's 1989 film UHF . Some Pioneer GGV1069 LaserDisc reference discs released for the NTSC market included a variant of the card, but modified with a gray-colored grid and a drawing of a Japanese lion-dog replacing the Indian-head portrait. It was sold as a night-light from 1997 to 2005 by

2320-602: The mid-1970s. This version eschewed the Indian head drawing with the TNT-9 station ID on top, similar to the aforementioned KRLD-TV, WBAP-TV and WKY-TV variants. Saudi Broadcasting Authority in Saudi Arabia also formerly used a modified version of the Indian-head test pattern, with the Emblem of Saudi Arabia replacing the Indian head drawing, from 1954 until 1982 when it was replaced with

2378-500: The monoscope-created control image. The test pattern was useful for the calibration of home television sets as well as television studio equipment, so the image was routinely broadcast outside hours of programming . (It was often accompanied by an audio test tone for the purposes of calibrating aural system frequency response measurements. ) From the late 1950s the test pattern gradually began to be seen less frequently, after fewer sign-offs, on fewer stations, and for shorter periods in

Stratovision - Misplaced Pages Continue

2436-557: The morning, since new and improved TV broadcast equipment required less adjusting. In later years the test pattern was transmitted for as little as a minute after sign-off while the transmitter engineer logged required Federal Communications Commission -US/ Board of Broadcast Governors transmitter readings before cutting power. The Indian-head test pattern became obsolete in the 1960s with the debut of color television ; from that point onward, an alternate test card of SMPTE color bars (and its immediate predecessors), or colorized versions of

2494-685: The other U.S. programs. The project is being handled by the U.S. Navy . Also involved are the U.S. Information Agency and the Agency for International Development . Work on modifying two Lockheed Super Constellations has been underway by Navy electronics experts at Andrews Air Force Base ... The project is an outgrowth of a broadcasting plane used by the Navy during the Cuban and Dominican Republic crises when both radio and television were beamed to home in those countries. The same article went on to report that during

2552-486: The other side referred to lines of resolution. The gray bands emerging from the center off to the lower right and upper left were for differential gain, contrast, and white level. The pattern began with the Indian-head portrait created in August 1938 by an artist named Brooks using pencil, charcoal, ink and zinc oxide . For about a year, the portrait (which contains several identifiable shades of gray from Zone VIII texture in

2610-699: The playing of " God Save the Queen " at closedown. This test pattern was later used by the Venezuelan TV channel Venevisión , in conjunction with the RMA Resolution Chart 1946, until the late-1970s before signing on with the Venezuelan national anthem . Telesistema Mexicano (now Televisa ) stations also used this test pattern until the late-1960s immediately after playing the Mexican national anthem at sign-off. In

2668-401: The presence of buildings and forests. Low-powered microwave transmitters can be foiled by tree branches, or even heavy rain or snow. The presence of objects not in the direct line-of-sight can cause diffraction effects that disrupt radio transmissions. For the best propagation, a volume known as the first Fresnel zone should be free of obstructions. Reflected radiation from the surface of

2726-414: The presence of obstructions, for example mountains or trees. Simple formulas that include the effect of the atmosphere give the range as: The simple formulas give a best-case approximation of the maximum propagation distance, but are not sufficient to estimate the quality of service at any location. In telecommunications , Earth bulge refers to the effect of earth's curvature on radio propagation. It

2784-518: The radius of the Earth and h be the altitude of a telecommunication station. The line of sight distance d of this station is given by the Pythagorean theorem ; The altitude of the station h is much smaller than the radius of the Earth R. Therefore, h 2 {\displaystyle h^{2}} can be neglected compared with 2 ⋅ R ⋅ h {\displaystyle 2\cdot R\cdot h} . Thus: If

2842-448: The refractive effects of atmospheric layers, the propagation paths are somewhat curved. Thus, the maximum service range of the station is not equal to the line of sight vacuum distance. Usually, a factor k is used in the equation above, modified to be k  > 1 means geometrically reduced bulge and a longer service range. On the other hand, k  < 1 means a shorter service range. Under normal weather conditions, k

2900-706: The rise of color television in the 1960s. The Indian-head test pattern was created by RCA at their factory in Harrison, New Jersey . Each element of the card was designed to measure a specific technical aspect of television broadcast so that an experienced engineer could, at a glance, identify problems. The card contains elements used to measure aspect ratio, perspective, framing, linearity, frequency response, differential gain, contrast, and brightness. The grid and circles were used for perspective, framing and linearity. The tapered lines (marked with 20, 25, 30, and 35) were used for resolution and frequency response. The thin lines marked from 575 to 325 on one side and 300 to 50 on

2958-510: The service range of a station at an altitude of 1500 m with respect to receivers at sea level can be found as, Indian Head test card The Indian-head test pattern is a test card that gained widespread adoption during the black-and-white television broadcasting era as an aid in the calibration of television equipment. It features a drawing of a Native American wearing a headdress surrounded by numerous graphic elements designed to test different aspects of broadcast display. The card

SECTION 50

#1732849111878

3016-580: The speakers on the TV sets would need to be amplified if they were going to be heard by a room full of people watching THVN -TV channel 9. The U.S. programming on NWB-TV channel 11 was Bob Hope in a two-hour special called Hollywood Salute to Vietnam , followed by half-an-hour of the Grand Ole Opry and another half-hour of the quiz show I've Got a Secret . The regular line-up of shows included Bonanza , Perry Mason , The Ed Sullivan Show , and The Tonight Show Starring Johnny Carson . EC-130 Commando Solo

3074-443: The surrounding ground or salt water can also either cancel out or enhance the direct signal. This effect can be reduced by raising either or both antennas further from the ground: The reduction in loss achieved is known as height gain . See also Non-line-of-sight propagation for more on impairments in propagation. It is important to take into account the curvature of the Earth for calculation of line-of-sight paths from maps, when

3132-528: The transmitters in the interior of the aircraft would have generated a temperature of 134 degrees Fahrenheit (57 degrees Celsius) with an outside air temperature of 25 degrees Fahrenheit (minus 4 degrees Celsius). On 23 June 1948 the system's airborne transmitter rebroadcast the Republican National Convention , being held in Philadelphia, Pennsylvania , to the surrounding nine-state area during

3190-406: The white feathers to Zone II texture in the black hair) was the entire test pattern, but in 1939 the portrait was incorporated into the current pattern of calibrated lines and shapes. Television stations would produce the image of the Indian-head test pattern in two ways. First, they would use a monoscope in which the pattern was permanently embedded, which was capable of producing the image with

3248-410: Was created by RCA to be the standard image for their TK-1 monoscope , a simple video camera capable of producing only the image embedded within it. The pattern was introduced in 1939 and over the following two decades became a fixture of television broadcast across North America in 525-line resolution and (often in modified form) abroad in 525- and 625-line resolution until it was made obsolete by

3306-497: Was undertaken by these companies using a stripped-down B-29 Superfortress flying at 30,000 feet (9.1 km). The plane was equipped to receive a relay transmission from WMAR-TV in Baltimore, which was then relayed over a 5 kW video transmitter and a 1 kW audio transmitter for reception on 82-88 MHz with a television set tuned to Channel 6. The aircraft received its originating signals from circular dipoles attached to

3364-614: Was used in propaganda warfare during the 1999 NATO bombing of the Federal Republic of Yugoslavia with questionable success. Production was very cheap, below local TV standards in Federal Republic of Yugoslavia with slide show and narration based news. Quality of reception was very poor and area of coverage was rather small. During the 2000s, the EC-130 Commando Solo has been used to broadcast information and propaganda for

#877122