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arrangement rotated 90 degrees in order to be sensitive in elevation and not angle. This portion was two dipoles wide and six dipoles high with corresponding reflectors. Finally in the "middle" of the cross, between the upright pedestal and the elevation antenna, was the broadcasting array which created a circular beam about 10 degrees wide.
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for support. Two towed the radar base and the antennas themselves, another pulled a K-34 trailer van providing power, and the fourth a van that converted the power to high voltage for the radio equipment. In total, including the trucks, the SCR-268 weighed 82,315 pounds. That the system was mobile at
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The radar operated at 205 MHz with a PRF of 4098 pulses per second of 6 μS (microsecond) duration, with an inter-pulse time of 240 μS. Radio waves (light) travel at about 0.093 miles/μS round-trip, so the system had a 22 miles (35 km) maximum range (240 × 0.093). It broadcast
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in the early 1920s. William D. Hershberger duly went to see what they had, and returned an extremely positive report. They decided to try to find a need for such a unit in order to gain funding, and eventually received a "request" by the Chief of Coast
Artillery on February 1, 1936 for a gunlaying
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Range information was taken from the elevation array, and worked, as it did for most radars of the era, by triggering the trace on an "A-line" oscilloscope and read against a scale at the bottom. A second blip was also generated by equipment attached to the rangefinder's handwheel. By rotating the
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The accuracy of the antennas themselves was not very high, about 9-12 degrees, so simply rotating the antenna and looking for a maximum would not point it very accurately. To help with this the antennas were deliberately designed to have two directions of high sensitivity, or "lobes". Signals from
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elements arranged in three groups, each in front of a passive reflector, mounted on a large aimable cross. The cross consisted of a short upright pedestal sitting on top of a large base platform, mounting long cross-arms extending from the midpoint of the upright pedestal. The antenna system was
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The left side of the cross arm, as seen from the back, contained a set of dipoles that were set to be sensitive in angle, while almost insensitive to elevation. It was arranged six dipoles wide and four dipoles high, each with its own reflector. On the far right side was a similar, but smaller,
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The system also included two sets of "repeaters" that sent the directional information to a searchlight, and both the directional and range (as dialed in on the rangefinder's handwheel) to a gun. The accuracy was not enough for direct gunlaying, but in combination with a searchlight the gun's
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Gaining the support of James B. Allison, the Chief Signal
Officer, they managed to gather a small amount of funding and "stole" some more from other projects. By December 1936 they had a working prototype, which they continued to work on and improve. On May 26, 1937 they were able to show the
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The SCR-268 was combined with the Sperry M-4 gun director to create automatic radar-controlled gun laying; however, the relatively long wavelength (1.5 meters) resulted in poor accuracy. This system was eclipsed by the
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display. One controlled the azimuth, another the elevation, and the third measured the range. Pointing the antenna was controlled by rotating large handwheels, the range being reported by a similar wheel.
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of its receiving antennas as a means to aim AA (anti-aircraft) searchlight beams at aircraft. Since it did not lobe-switch its transmitted signal it would be classed as one of the first LORO (
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both lobes were displayed, slightly separated, on the layer's displays. By adjusting the antenna until the returns from both were equally strong, accuracies of about one degree were possible.
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radars based on the "beat principle", in which an aircraft would cause two signals to interfere. Low generator efficiency and a lack of ranging capability made these efforts impractical.
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handwheel until the reference blip overlapped the one returned from the antenna, the timing could be read from the wheel. Range accuracy was about plus or minus 200 yards.
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about forty feet wide and ten feet high overall. Both the pedestal and the cross-arm could be rotated around their axis for aiming, in azimuth and altitude respectively.
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Development of this system was slowed to some degree when a long range early-warning radar became a higher priority and parts of the prototype were salvaged for the
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bomber where it was supposed to be, they started "hunting" for it and found it 10 miles off course. The radar fed pointing data to a team operating a
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detection systems (a popular idea at the time), as well as a newer generation of sound detectors, they also maintained a small program of research on
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Three soldiers of the United States Army operate a radar used by the 90th Coast
Artillery (Antiaircraft, Semimobile, Colored) in Casablanca
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system. Introduced in 1940, it was developed to provide accurate aiming information for antiaircraft artillery and was also used for
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about the same time as the -270 in 1939. The radar entered service in 1940, and about 3100 were produced by the end of the war.
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The three radar operators sat at consoles mounted on the pedestal just below the antenna cross-arm, each with their own
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In 1935 one of Blair's recent arrivals, Roger B. Colton, convinced him to send an engineer to investigate the
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had been experimenting with some radar concepts as early as the late 1920s, under the direction of
Colonel
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Oscilloscope operators with range scope at left, azimuth scope in middle, and the elevation scope at right
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the system was already considered out of date, having been replaced by the much smaller and more accurate
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all was more a testament to the US's overwhelming industrial might than any quality of the radar itself.
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about 75 kW of power, which was, in theory, more than enough to offer longer range.
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Mindell, David A., "Automation's Finest Hour", IEEE Control
Systems Magazine 15(6)
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project. The navy's system traced its development from experiments conducted by
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461:, Electronics magazine, September 1945. A detailed description of the system.
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prototype in a convincing demonstration. After failing to find their target
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http://www.monmouth.army.mil/historian/photolist.php?fname=Radar%2FSCR-268
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system with a range of 15,000 yards through rain, mist, smoke or fog.
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existing optical equipment could "fine tune" the radar's guidance.
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they were building. Nevertheless, the system entered production at
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against aircraft. The radar was widely utilized by both Army and
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oscillator from
Britain, completely automatic tracking, and the
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http://www.history.navy.mil/library/online/radar-5.htm
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There are no known surviving examples of this array.
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The SCR-268 antenna system consisted of a number of
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516:Military radars of the United States Marine Corps
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475:http://www.mobileradar.org/radar_descptn_2.html
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204:air defense and early warning units during
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80:Learn how and when to remove this message
43:This article includes a list of general
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280:United States Naval Research Laboratory
358:The radar was mobile, requiring four
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506:Military radars of the United States
412:List of U.S. Signal Corps Vehicles
49:it lacks sufficient corresponding
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371:, which utilized a 3 GHz
27:U.S. Army's first radar system
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377:Bell Telephone Laboratories
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104:SCR-268 radar deployed on
464:TM 11-1106,1306,1406,1506
245:Signal Corps Laboratories
159:22.7 miles (36.5 km)
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278:and Leo C. Young at the
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114:Country of origin
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151:7 to 15 microseconds
511:World War II radars
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422:Signal Corps Radio
398:Surviving examples
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243:, director of the
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186:United States Army
180:Signal Corps Radio
501:Gun laying radars
459:The SCR-268 RADAR
208:. By the end of
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304:Western Electric
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241:William R. Blair
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379:electronic
310:Description
293:searchlight
289:Martin B-10
231:Development
106:Guadalcanal
70:August 2013
62:introducing
495:Categories
453:References
394:) radars.
272:CXAM radar
253:New Jersey
194:gun laying
184:) was the
148:Pulsewidth
124:Introduced
45:references
427:G-numbers
373:magnetron
261:microwave
257:infra-red
217:microwave
188:'s first
140:Frequency
406:See also
369:SCR-584
300:SCR-270
268:US Navy
214:SCR-584
182:no. 268
175:SCR-268
93:SCR-268
58:improve
18:SCR-268
324:dipole
47:, but
482:pics.
433:Notes
190:radar
177:(for
164:Power
156:Range
235:The
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132:Type
127:1940
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