Ekco Red Steer radar

[overscan (PaulMM)]

Red Steer – ARI 5919 & ARI 5952

By Chris Poole December 2007

Red Steer (ARI-5919) evolved from AI Mark 20 -- code named Green Willow which was the designation given to the EKCO fire control radar developed as a back up to the AI Mark 23 radar being designed by Ferranti for the English Electric Lightning (then known as the P1), which was under development in the early 1950's.
While this radar system (AI-20) performed well and exceeded the system requirements, it was only ever a development contract and once AI-23 came 'on stream', work ceased. However a year later (in 1956) a RFQ (Request for Quotation) was issued for a Tail Warning Radar (TWR) for the V Bomber fleet as part of the ECM (Electronic Counter Measures) suite.
Note: the V Bomber fleet consisted of the Vickers Valiant, the AVRO Vulcan and the Handley Page Victor.
Fortuitously, the team at TRE Malvern (soon to become the Royal Radar Establishment Malvern) recognised that the EKCO AI-20 unit was a well engineered set, which, with a minimum of re-design could be adapted to suit the TWR requirement and at the same time significantly reduce both the development cost and more importantly the time taken to get the unit in service -- bearing in mind that at this time the 'cold war' was at it's height and there was an urgent need to get the V Bombers fully operational to act as the nuclear deterrent.
The result of this was that with the support of the RRE EKCO liaison officers, particularly Jerry Steer, EKCO was awarded the contract for the TWR, which was code named Red Steer and given the RAF reference number ARI-5919
The Red Steer team was essentially the same as for AI-20 (headed up by Cyril Drew assisted by Bill Graville, Eric Alden and by this time also joined by Maurice Wedd as the lab gofer -- (please see the AI-20 write-up for more details of the people involved) and effectively concentrated on improving the magnetron performance to 130Kw, reducing the signal noise ratio (improving the IF unit), re-designing the scanner unit and improving the wave-guide run to eliminate loses. Work took place in 'me-ladies bedroom' at Cowbridge House Malmesbury.
The unit, which evolved from this was the most powerful and complex 'valve' era radar ever made by the company and possibly the most secret, so secret in fact that most of the work was done on a strictly 'need to know' basis even down to shop floor level. An example of this is the fact that when production testing needed 'power runs' these mostly took place in the evenings when the staff had gone home with such power runs made pointing the unit down the length of the assembly hall, which had the interesting effect of lighting up all the overhead fluorescent tubes such was the microwave energy. Most testing however was done using a dummy load and an Echo test box designed by Mike Skinner, this unit also being used by the RAF when doing front line servicing 'in situ' on the flight line.
The block diagram shown below is a fair estimation of the complexity of Red Steer and shows in general terms how all the different modules are co-related.

In engineering and manufacturing terms, there were no real problems over and above those already worked through on AI-20 with the exception that a persistent problem was discovered with 'arc over' in the waveguide block (which was a large complex structure machined in two halves to great accuracy and bolted together) the problem being identifying where and why. This was solved in a rather novel manner by one of the waveguide team called 'John Fitzgerald' who hit on the idea of obtaining cigarette paper in large sheets and trapping it between the two halves of the waveguide block. Arc over then burnt the paper and showed where it happened and a look at the corners of the 3db coupler soon showed why. Problem solved.
The use of new fangled NPN silicon transistor were evaluated during the design stage of the gating unit by Mike Skinner since they provided much less change of parameter with temperature and higher frequency response. Previously they were all PNP germanium although the circuits really need both NPN and PNP forms.
Maurice Wedd remembers that when a silicon PNP transistor became available there was great excitement and with RRE help the lab got one of the rare Silicon PNP Transistors and he was asked to wire it into Mike's prototype circuit. Yes you guessed it. -- he wired collector and emitter backwards and upon switch on, by Mike, it blew. So was the colour of the air.
Another issue to solve was the 30Kv DC cabling bringing the signal to the indicator unit from the T/R unit (in the tail). The RAF were very nervous of this especially since the cable ran the length of the fuselage and passed near fuel lines as well as the armament and with the high altitudes being flown the potential for arcing needed to be eliminated with all the cabling connections. This resulted in special couplings having to be designed and manufactured, which were tested in a vacuum to check for arcing. The result being that in service they proved to be faultless.
By January 1958 the unit was ready for trials and while the exact performance details amazingly are still subject to the Official Secrets Act under the 30 year disclosure rule, the unit was known to be able to demonstrate that that there was a 75% certainty of detecting a Hawker Hunter size aircraft making a 'straight tail on' approach at 10 nautical miles with this raising to 100% certainty of detection at 8 nautical miles.

ARI-5919 indicator unit positioned in the AEW (Air Electronics Warfare) suite of the V Bombers
and controlled by the AEO (Air Electronics Officer).

As can be seen above, the operator saw the interceptions through a round display unit, which had three pre-set ranges i.e. Range 1, 0-5 Nm, Range 2, 0-10 Nm and range 3, 8 to 18 Nm. The image was produced via an 18 inch scanner dish producing a spiral scan radar beam in X band, with a 5.5º degree beam width and a high PRF (actual PRF value still classified). The scanning pattern producing a 90º degree cone coverage behind the aircraft.
The result of this is that the indicator unit showed the range as an 'inside-out display' i.e. with the minimum range at the outside of the display screen and the maximum range at the centre. While this took a while to get used to it did have an advantage that as targets got closer, the image got larger and discrimination was better.
The set was normally operated in the 'standby mode' during operations to avoid emitting any radar signal and only switched on (TX mode) when the radar threat receiver (positioned alongside this unit) indicated that the aircraft was being scanned by hostile 'airborne radar'.

Illustration of Red Steer Mk 1 (ARI-5919) Indicator unit.
The Red Steer Mk1 Spiral scan system was displayed with an outer ring, which always represented 'Minimum Range' irrespective of what range was selected by the operator.
There were three ranges, thus: -
Range 1 equalled 0 to 5 Nm -- range markers at 2Nm intervals
Range 2 equalled 0 to 10 Nm -- range markers at 4Nm intervals
Range 3 equalled 8 to 18 Nm -- range markers at 4Nm intervals
Targets were shown as inner circles when the target was target dead astern and as segments when 'off beam'.
For example: -
An attacker 3 degrees off would show as a 180-degree arc
An attacker 5 degrees off would show as a 90-degree arc
An attacker 10 degrees off would show as a 30-degree arc
An attacker 20 degrees off would show as a 15-degree arc
An attacker 30 degrees off would show as a 10-degree arc
An attacker 45 degrees off would show as a 5-degree arc.

Example 1 Range set at 0-10Nm, dotted Inner circles equal 4Nm and 8 Nm range markers, target approximately 5 miles dead astern.
Example 2. Range set at 0-10Nm, dotted Inner circles equal 4Nm and 8 Nm range markers.

ARI-5919 remained in front line service until the late 1960's when the RAF changed their policy on high-level penetration in the face of experiences learned from the USAF in Vietnam where high altitude B52's were being downed by missiles and the new doctrine was to be 'low level' which meant that the whole of the ECM suite on the V bombers needed to be updated not only because of the new threats but also the new operating regime.
Resulting from this ARI-5919 was redesigned with a new scanner unit and a new indicator unit. While the original T/R unit was retained, this was considered a major redesign by the RAF and as such was allocated a new ARI number, this being ARI-5952.
The scanner unit was a version of the M2269 scanner unit as used on the civilian E190 weather radar but with a re-designed gearbox casting, which mated onto the existing pick up points of the original radar scanner thus eliminating expensive alteration to the existing T/R unit.

ARI-5952 scanner unit on display at Bruntingthorpe -- Photograph courtesy of Maurice Wedd

The major advantage of this unit was that it had a 'Raster scan', a 150º degree azimuth sweep and a +25º beam tilt, which meant that a large section of sky behind the aircraft could be scanned.
The scanner was fully 'line of sight' stabilized and had a scan rate of 40 scans per minute, this together with a 24 inch dish (giving a beam-width of 3.7ºdegree's) gave a very good high fidelity target return together with an improvement in detection range. Exceptionally smooth control could be maintained on the scanner dish due to the high degree of stabilization and the lack of 'servo drag', which was held to better than 1º degree over the whole range of pitch or roll.
This fine control on the scanner dish was especially useful when the AEO (Air Electronics Officer) operated the set in 'sector scan mode' i.e. manually controlling the scanner unit to focus on one small area of sky in order to focus in on a target.
Along with the re-designed scanner unit, the indicator unit was a heavily modified M2212 indicator unit designed by the late Gordon Simons, and again taken from the civilian E190/E290 weather radar systems.
Unlike the 5919-indicator unit, this unit needed a much lower EHT feed at 18Kv (designed by Jack Halsall el al) and benefited from the use of a new screen phosphor CRT, which gave an exceptionally brilliant display. The next advantage was display size (5X3 inches) and the simplicity of reading the display.

Indicator unit in Vulcan XM655 at Wellesborne -- Photograph courtesy of Derek Powell

The testing of the new unit was not without tribulations since the initial testing was done at RSRE Pershore and was the first time the indicator and the video output from the T/R unit was tried for the first time against real targets.
This immediately showed up a major problem since the whole screen lit up and was saturated by the strong return from the Malvern Hills.
This fault however was quickly recognized since Gordon Simons had not used any form of DC restoration on the video amplifier, which resulted in the video signal being saturated. Maurice Wedd well remembers that this resulted in a fast trip back to Southend for a modification (Note, by this time R&D; and production had moved away from Malmesbury to Southend on Sea).

General view of AEO position in Vulcan XM655. Note the small white screen to the right of the TWR unit
is the radar threat screen. This screen showed if the A/C was being painted by hostile radar.
Photograph courtesy of Derek Powell

ARI-5919/5952 had a long service life and remained in service for as long as the V Bombers were flying, which meant of course that the unit was flown down to the Falklands in XM607 (in 1982) although the unit failed during the mission due to the casing suffering pressurisation failure because of the long flight duration (15 hours+), which far exceeded the design parameter for pressurisation.
Later the unit saw service again during the first gulf war in 1992 -- flying in the tail of the HP Victor 'air to air' refuelling aircraft, which meant that not only was the radar older than most of the aircrew, the T/R unit was some 38 years old from the date it was originally first conceived in 1953 in Cyril Drew's lab at Malmesbury. Not bad for a 'valve system' and not only showed the soundness of the design but also the quality of the workmanship from the EKCO team at every level.
Red Steer was officially retired from service in 1994 and the units either being broken up, sold with the remaining Vulcan's, which are now museum pieces and the unit with XH558 at Bruntingthorpe (the Vulcan restored to flying condition) has been on public display during open days and the Vulcan XM655 team at Wellesborne also hope to display a Red Steer in the future.
Interestingly while there are units on public display, due to the 30-year secrecy rule on documentation, the associated manuals are still 'restricted' and will not be publicly available until 2024.

Archived from http://www.ekco-radar.co.uk/poole/redsteer.php