| Radar
Anti-Aircraft No. 3 MK.
7 - Blue Cedar (UK) |
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AA3
MK7
mobile radar
cabin after external restoration, June 2007
The
mobile
radar unit pulled by an AEC Militant Medium Recovery Vehicle.
When in service, the radar unit was towed by an AEC Matador Medium
Artillery Tractor
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Equipment
information
The
AA3 MK7 was a mobile trailer-mounted,
second level, anti-aircraft gun control radar station,
the original design of which
dates from
the mid 1940s. The equipment design was in use with various
UK
and Commonwealth Armed Forces until the mid 1970s.
The UK code name for this
equipment was Blue Cedar.
The radar was originally used to control
anti-aircraft guns Type 5.25 inch and
Type 3.7 inch in elevation, height and range via an intermediate
mechanical computing device known as an AA Predictor. AA3
MK7 is
capable of detecting a Spitfire at 25,000 yards and planes the size of
a
Beaufighter or larger at 36,000 yards.
The
radar station is housed in
a steel, air-conditioned,
four-wheel
trailer which carries a rotating 5ft parabolic dish antenna on the
roof. The
radar trailer weighs approx 5.125 tons and has dimensions of length 15
ft, height 12 ft 9 ins, width 12 ft.
The
frequency range of operation
is 3.0-3.1G Hz (9.7-10cm) with a
transmit output power of 200kW peak, which gives a detection range
between 950-36,000
yards. The antenna
rotates at 20RPM and also
executes
an elevation scan every 4 seconds.
The system can operate
in either search mode or tracking mode. This
means that the station can both acquire and track moving targets in
range, elevation and azimuth bearings.
Electrical power is obtained
from a separate trailer-mounted
three-cylinder Lister/Tilling-Stevens
diesel
generator, type X2/X8/17472, which can supply
17k VA three phase AC at 240 Volts 50c/s.
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Equipment
background story
This
particular radar unit was built by the British Thomson Houston Company
and has serial number 223
on its identification plate.
After use by the British Army
Anti-Aircraft Command it was supplied to
the Netherlands Armed
Services.
After service in Holland it was
subsequently transferred to the Air
Defense
Regiment
of Ireland and was used as a mobile air defence radar.
Following completion of its
active service in Ireland
it was donated to the Winbolt Collection. It has spent approx the
last 8
years or more stored in the open at Bletchley Park.
It is complete with its trailer
mounted diesel generator (dated 1952
with 12 hours operation on the clock),
target
simulator
equipment and some of the original documentation.
IWM
Duxford already has on display two examples of the type of large
anti-aircraft
gun which
was controlled by this radar unit (AA
Gun Type 3.7 inch).
One can be seen in Hangar
4 finished in deep bronze green,
and a second in the Land Warfare Hall.
An informative public display
would be the radar
station exhibited alongside the matching 3.7 inch AA gun to show the
complete 1940s/1950s mobile Anti-Aircraft station.
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Conservation
& restoration process
This
equipment was kindly donated to DRS by Dr. G. E. Winbolt.
The
external conservation of this complete mobile radar
station began with maintenance work by DRS Volunteers on the
diesel engine of
the generator trailer and work to repair the roof of the main
Radar cabin. As the equipment has to stand outside for the
foreseeable future, the priority was to protect the exterior of the
station.
During
August 2006 the diesel generator was moved to the Duxford
Aviation Society
Military
Vehicles Section in
the Land Warfare Hall at
Duxford to be overhauled, stripped,
resprayed and serviced by the DAS Volunteers from this Section.
Volunteers from the Radio Section began work on the electrical
components. The generator exterior restoration was finished in
December 2006. Work continues on the electrical, control and
metering equipment.
On 18 September 2006 the radar
trailer was also moved to the DAS Military Vehicles
Section ready to begin its
mechanical restoration and overhaul.
The exterior
restoration was finished in early February 2007. See photos
below.
After the external mechanical
restoration, if a covered area to work
can be
found, it intended that the power supplies
will be gradually
applied to the
main radar
trailer to
enable the heaters and air conditioning plant to operate and therefore
maintain the cabin interior in a dry state. Conservation work can
then start on the internal equipment modules.
On 24 January 2008 the custom made canvas cover or 'Tilt' for the
diesel generator arrived for first fitting.
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Photographs of Radar AA3
MK7 Blue Cedar taken in the afternoon light, January 2008
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Radar
AA3 MK7 with matching 17KW diesel generator
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View
of the radar station from the other side
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Close-up
view of radar cabin 1year after re-painting
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Close-up
of generator with custom cover fitted
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AA3 MK7 Restoration Project
Sequence Photographs
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Rear
view of radar cabin while in
storage at Bletchley Park
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Front
view of radar cabin
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Part
of radar cabin interior
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17
kVA diesel generator trailer
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AA3MK7
radar cabin and Generator trailer being delivered to Duxford from
Bletchley Park
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Radar
cabin with the DRS team of "youngsters"
From left to right: Arthur Llewellyn, Denis Willis, Dennis Harvey
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| Mobile radar
cabin before restoration, September 2006 |
Working on the
diesel generator March 2006 |
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Diesel
generator in the DAS Military Vehicles
Section workshop
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Diesel
generator front view
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Rear
view of diesel generator
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Electrical
control panel partly dismantled |
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Mechanical
assembly after top coat of Deep
Bronze Green paint
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Diesel
generator front view
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Rear
side view of diesel generator
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Other
side view |
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Radar
trailer pulled by the DAS MV Section AEC
Militant Medium Recovery
Vehicle (called "Milly"). Since this shot was taken, Milly has
been finished in a nice deep bronze green paint finish.
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Radar
trailer parked outside the IWM Duxford
Land Warfare
Hall in the queue of vehicles waiting for attention
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Adding
some of the fine paint details to the
generator engine paint finish
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Now
the engine has to be made to start well
and run reliably
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AA3
MK7 radar trailer in the DAS MV Section
workshop ready for dismantling and restoration to start
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DAS
MV Section Volunteers working on the radar trailer. Note the
emergency exit door at right. |
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| View
through the emergency exit door showing
the antenna mounting, the main support shaft, waveguides and cableforms
etc |
Rear
view of radar trailer showing progress
made on the cleaning, sanding, de-greasing and primer stages
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Right
hand side view of the new paint
finish. The Military Vehicles Section do a really excellent
job.
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The
exterior restoration is nearly finished now. Just the small
details to be highlighted and the wooden decking on the roof to be
re-fitted |
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View
inside one of the electronics modules
inside the radar cabin
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Close-up
view of the same module - some corrosion to be gently dealt with in here
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| Side
view of finished radar cabin after
restoration taken on a
damp morning in February 2007 |
Rear-side
view.
The wooden decking has now been painted and re-fitted on the roof
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Rear
view showing the motor drive
assemblies for the dish
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Front
view showing the towing and steering gear
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Radar cabin with diesel generator behind
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Side
view of radar unit with dish mount raised and tilted over into the
operating position
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| Three-quarter
side view of finished unit |
Radar
and generator unit from side
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Work is
still
ongoing on the electrical control gear of the mobile generator
trailer. The diesel engine needs further attention. A
replica of the correct canvas cover for the diesel generator has now
been fitted.
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Work has now
started to conserve the electronics modules inside the radar cabin. |
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