Radar, Anti-Aircraft No. 3 Mk. 7
PRF | 1500 pps | |
Pulsewidth | 0.5 μs | |
---|---|---|
RPM | 20 rpm while scanning | |
Range | 950 to 36,000 yd (870–32,920 m) | |
Diameter | 5 ft (1.5 m) | |
Power | 200 kW | |
Other Names | Blue Cedar |
Radar, Anti-Aircraft Number 3 Mark 7, also widely referred to by its development
Mk. 7 developed from experiments in the mid-WWII era on
The unit was housed in an air-conditioned trailer that was significantly smaller and more portable than the World War II-era SCR-584 and GL Mk. III radars it replaced; the Blue Cedar weighed about 5 short tons, compared to about double that for the SCR-584. It was normally towed by an AEC Matador artillery tractor unit, as opposed to requiring a semi-trailer. It could be emplaced and operational in under an hour, automatically feeding data though synchros to the gunnery computer and then directly to the guns.
Blue Cedar was the primary gun-laying system for the Army through the 1950s. Beginning in 1953, the air defence mission began to move from the Army to the
History
GL Mk. I & II
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/97/GL_Mk._II_radar_transmitter.jpg/220px-GL_Mk._II_radar_transmitter.jpg)
The
It quickly became clear that a range-only system was wasting considerable utility inherent to the design. Since the radar's signal spread over about 20 degrees, it observed a wide area of the sky and was able to detect targets before the crews on the optical instruments could. Additionally, it worked at night or in bad weather. This led to the GL Mk. II design which also measured angles with enough accuracy to directly lay the guns, removing the need for the optical instruments entirely. However, as this was not immediately available, a modification of the existing Mk. I's, the Mk. I/EF, was used until the Mk. IIs became more widely available in 1941.[4]
While these systems worked, they were unwieldy. The size of an antenna needed to efficiently broadcast and receive a signal is a function of the wavelength, so with the GL's ~4 m wavelength, antenna elements several meters across were needed. Focussing such a signal requires several such antennas, or one antenna and a suitable reflector, making the complete antenna system much larger. In the case of the GL radars, the antennas were supported on large steel frameworks about 10 m across, rather less portable than desired.[4]
GL Mk. III
The introduction of the
Initially, most work with the magnetron was focused on airborne roles, where its small size was an enormous advantage. However, as the winds of war changed, there was increasing demand for a new anti-aircraft radar that could replace the existing GL's with something that was far more practical, and in particular, much more mobile. In November 1940 the magnetron had been demonstrated to Canadian and US researchers, both of whom had begun developing their own versions of GL based on it. After some initial work, the three countries agreed that Canada and the UK would work on a simple system that could be deployed as quickly as possible, while the US would work on a much more advanced system.
The result of all this work was the
Technical developments
As the Mk. III's were being designed, two new concepts were being developed that greatly improved radar designs.
The first advance came as part of the development of airborne microwave radars. The Mk. 3 used separate transmit and receive antennas because they lacked a suitable way to rapidly switch the antenna feed from the transmitter to receiver. Using two reflectors was not going to work on aircraft, and the
The second was part of the development of lock-follow systems. At the end of 1940, the Army began introducing its latest radar, the Searchlight Control radar (SLC). This was a simple system that was attached directly to a searchlight to allow it to easily find targets at night. The system used a unique arrangement of four antennas connected together in pairs, up/down and left/right. Three operators were required, each with their own CRT display. One display received the signal from all four antennas, showing every target in the area, and its operator selected one for tracking. The other two CRTs received the signals from the up/down, left/right pairs. By comparing the height of the blips, their operators could see which antenna was closer to the target, and turn the light in that direction to track it.
In 1941, an engineer at BTH, L.C. Ludbrook, began development of a lock-follow system for the SLC. This used simple electronics that were fed the paired signals and output a current whose magnitude depended on the amount of difference between the two. This signal was then sent into amplidynes that amplified the signal and drove motors that turned the light. Only a single operator was needed; they selected a target on their CRT, and then the rest of the operation was completely automated. This was not only more accurate, but it also eliminated two crewmen and their CRTs, both of which were in short supply.
Ludbrook's system was not put into production for the SLC systems, but the idea quickly caught the interest of the entire radar establishment. A number of different designs using different underlying electronics or drivers were introduced around the same time. There was a brief attempt to adapt the Canadian Mk. IIIs to use auto-follow, but as this system swung the entire cabin around to track, the power required to drive the pointing motors was huge. Lock-follow was experimented with on the British Mk. IIIs, which turned only the antennas, producing the 3/1 and 3/3 models. Both efforts were eventually abandoned.
Instead, it was decided to combine lock-follow and the Sutton switch into a new set, which began development in 1942.[5] As part of a general reorganization of their radar efforts, the Army renamed the existing Mk. III sets as the AA No. 3 Mk. 1 for the Canadian sets and Mk. 2 for the UK versions. The new design was given the name AA No. 3 Mk. 4.[a]
SCR-584
By 1943, the US project had produced the
The SCR-584 was originally expected in late 1943, before the Mk. 4, which was then put on low-priority development. However, the sets did not begin to arrive in significant numbers until the middle of 1944. As the delays grew, the Mk. 4 was put back into full development, and the first prototypes began to arrive in 1944, just as the supply of the SCR-584 improved. Development was once again curtailed.
This all proved to be lucky timing, as the arrival of production SCR-584s was coincident with the start of the
Mk. 7
While the SCR-584 was an enormous advance on previous systems, it was also large and somewhat cumbersome. In the immediate post-war era, the magnetron saw rapid development and improvement, and new vacuum tubes were becoming widely available that combined multiple tubes into one. It was decided to re-engineer the Mk. 4 concepts with these new technologies, resulting in the Mk. 7 effort, which started in
The Mk. 7 was very similar to the SCR-584 conceptually but had a number of practical improvements. One was to use a parabolic reflector made of
Like most post-war Army projects, development of the Mk. 7 took place at a snail's pace. Estimates that another war would be at least ten years off suggested no major production should take place, as developments in the interim would render any radars built in that period obsolete. However, various events in 1949, notably the first Soviet atomic test, led to sweeping upgrades, including the first contract for production Mk. 7's. These began to arrive in 1952.
Other users
Switzerland
The
Specification
- 5 ft (1.5 m) diameter parabolic dish antenna rotating at 20 revolutions per minute.
- Elevation scan completed every 4 seconds
- Detection range 950–36,000 yd (0.9–32.9 km)
- Operating in S band 3.0 to 3.1 GHz
- 200 kW peak power.
- Powered by a Lister/Tilling-Stevens 17kVA diesel generator set housed in a separate trailer.
- Weight was about 5.125 short tons (4.576 long tons; 4.649 t).
- Height: 3.43 m
- Length: 5.75 m
- Width: 2.3 m
Notes
- ^ AA No. 3 Mk. 3 was an SLC radar adapted as an expedient gun-laying system before the SCR-584's arrived. The saw service only for a short time.
- ^ From outward appearance, the 43/50R appears to be a Kerrison Predictor.
References
Citations
- ^ "Radar Anti-Aircraft No. 3 MK. 7 - Blue Cedar (UK)". Duxford Radio Society. 24 September 2009.
- ^ "TULENJOHTOTUTKA VRRTI "SEVERI" (KALKKU), Tampere". Huutokaupat.com. Mezzoforte Oy. Retrieved 11 October 2019.
- ^ Honour 1981, p. 10.
- ^ a b Bedford 1946, p. 1119.
- ^ Bennett 1993, p. 149.
Bibliography
- Shore Radar Services (PDF). Air Ministry. October 1944.
- Bennett, Stuart (1993). A History of Control Engineering, 1930–1955. IET. ISBN 9780863412998.
- Bedford, Leslie (July 1946). "The development of gun-laying radar receivers type G.L. Mk.I, G.L. Mk.I* and G.L./E.F." Journal of the Institution of Electrical Engineers. 93 (6): 1115–1122. .
- Alber Wüst: Die Schweizerische Fliegerabwehr. 2011, ISBN 978-3-905616-20-0
- "Scientific Instrument Makers Honour Radar Pioneer". The Radio and Electronic Engineer. 51 (1): 10–11. January 1981. .
External links
- Mk. 7 training, IWM placeholder for Mk.7 training film