SCR-584 Technical Description

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This text was written by Ken Anderson, one time AN-FPQ6 radar supervisor at the Carnarvon Tracking Station.

The SCR-584, development of which began in 1941, could be operated in either a search or track mode. In the search mode the antenna was rotated through 360 degrees at 6 RPM. On each revolution the antenna elevation is raised so that it reaches a maximum elevation of 20 degrees in one minute. The result is a complete helical search of the space surrounding the radar.

Helical scan mechanism:Image – ‘Electronics’; Fig 2, Dec ’45, p.104
Helical scan mechanism:
Image – ‘Electronics’; Fig 2, Dec ’45, p.104
A conical scan beam: Image – ‘Electronics’; Fig 1, Nov ’45, p.104
A conical scan beam:
Image – ‘Electronics’; Fig 1, Nov ’45, p.104

There were three different scan patterns available for the antenna:

(a) a helical scan (see diagram to the right) in which the antenna scans the sky around the radar;

(b) a spiral scan in which the antenna beam spirals outwards from a designated azimuth and elevation and then back to the designated position until a particular target is located. This would be limited in extent, probably only 1 or 2 degrees maximum; and

(c) the rotation of the beam around the antenna's bore sight line provides a conical beam pattern (see diagram above left) which allows the system to determine the position of the target, and then automatically track it.

Nutating antenna dipole feed:A slightly-offset dipole antenna was rotated rapidly (nutated) to define the shape of the beam used in the three scanning patterns discussed above.Image – ‘Electronics’; Fig 5, Dec ’45, p.107
Nutating antenna dipole feed:
A slightly-offset dipole antenna was rotated rapidly (nutated) to define the shape of the beam used in the three scanning patterns discussed above.
Image – ‘Electronics’; Fig 5, Dec ’45, p.107

The angle scans, both the helical and the spiral, were generated by motor driven cams in the angle control panel. The caption on the photograph of the interior of this panel at refers to the angle control panel as a mechanical computer in the PPI unit. The analogue computer associated with the SCR584 was the M-9, a separate device.

The collected information was displayed on a Plan Position Indicator [PPI]. It allowed the operator to see all the radar returns on a map-like screen with the radar at its centre. On the console there were also two J-displays - a coarse-range display and fine-range display. Having designated the target on the PPI the operator could cause the antenna to carry out a spiral scan around the selected elevation and azimuth, and could thus locate a target.

Having located the target in angles the fine range display would then be used to differentiate between, for example a friendly fighter and enemy bomber and then allow the operator initiate automatic tracking of that target.

In the track mode the operator was required to adjust the rate of range change by operating a hand-wheel on the console. The Azimuth, Elevation, and Range analogue signals were fed to the external M-9 Gun Predictor. The M-9 was an analogue computer which solved the targeting problem and pointed the associated 90mm anti-aircraft guns so that the shell and the target arrived at the same spot simultaneously.

See 'Operator Instructions'

See: for The Test; a history of the SCR-584's use by the US Signal Corps.

See: for an explanation of the principles of Tracking Systems.

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