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E190 Weather Radar System
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By Chris Poole – January 2009 |
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Introduction |
In the summer of 1958 with the E160 safely launched, one of the most momentous decisions ever taken by EKCO Electronics was taken, this being to develop the world's first transistorised weather radar system and design this around 'ARINC' specification racking. |
This decision came about when in the spring of 1958 Phil Stride (Malmesbury MD) issued a request for ideas for possible future development since it was already apparent that MoD contracts were getting scarcer. Following a ballot of departmental heads VJ Cox put forward Static inverters, Fluorescent headlights for cars and a semi solid state (transistorised) next generation weather radar. |
As VJ recalls, fluorescent headlights were deservedly dismissed but both static inverters and weather radar went ahead. At that time both Jack Gard and VJ independently reported to Phil Stride. Although all previous Weather Radar work had been in Jack's section, the limited solid state experience and the new proposals came from VJ's side so this is where it finished. |
The Weather radar proposal at that time was pretty iffy. It was decided to keep the magnetron and hydrogen thyratron vacuum components and go solid state based on germanium transistors although their low maximum temperature gave cooling problems and necessitated forced air cooling for some of the display components. At the time, silicon transistors were rare and extremely expensive so could only be used in a few essential positions. |
The decision to base this future design on ARINC specification racking was a recognition that even in 1958 future generation aircraft electronics (avionics) racking would have to be based on this American standard rather than the existing SBAC racking, which was only used by a dwindling number of British aircraft manufacturers. |
The Use of Transistors |
Transistors had only been introduced into the company in 1955 when they were considered very much 'state of the art' and were very expensive. Some initial experimentation was done on a few limited applications for possible use on Red Steer although at that time it was decided not to proceed since this design was well advanced and not enough was known about how transistors would perform 'in service'. |
Nevertheless experimentation continued and one particular champion was John Yarrow a team leader from the Radar Labs where John introduced his lab personnel to the new world of transistors starting with point contact devices and then junction transistors from a wide array of manufacturers. Various lab personnel from all the labs also attended Bristol University for courses in transistors and their applications and this was supplemented by seminars and demonstrations from the transistor manufacturers, notably Mullard and Texas Instruments. |
The E190 Design Team |
Due to the fact that the E190 was going to break new ground in virtually every area, a multi-disciplined team was set up with the remit to push ahead as fast as possible so that the E190 could be introduced into service ahead of anything being worked on by the Americans. |
Jack Halsall (from Jack Gard's lab) was appointed project leader and he was joined by Dennis Williams, Mike Skinner and Mike Rose as well as some other engineers also from Jack Gard's lab. A lab was set up at Malmesbury in what was called the 'Nursery', which was the top floor middle lab. Frank Burnill took on TR design supported by Tim Gummer. Video signal processing by circuit design was taken on by Mike Skinner (ex Cyril Drew's Radar Team). Jim Cox (VJ) designed the layout of the indicator which remained virtually the same throughout its life on the back of a postcard in best Parker 51 ink pen style. |
John Yarrow was not a direct member of the E190 team, but he assumed the role of mobile consultant visiting the various jobs giving advice and helping problem solve issues when asked. VJ would also visit the labs often on a daily basis with sketches and possible circuits. If not in the lab, as often as not he would be in the Senior Engineer's room where discussions also took place. |
The transformers were initially designed by Ian Walker and latterly by John Clarke working in conjunction with the lab engineers to get the weights down. Mike Rose was especially influential in this transformer design team where he did a lot of ground breaking work on resin encapsulation technology in conjunction with the 'potting shop'. |
As usual, Norman Wall and his team designed the IF strip, which presented particular problems since at that time 45MHz or higher was accepted centre frequency. Suitable transistors were not then available so this forced the use of a much lower frequency (13.5MHz). This brought with it an assortment of second order problems. Although this was kept under control (just!) it was never very satisfactory and, about a year later, when suitable transistors became available it was redesigned for 30MHz. which incidentally was the only major change in the E190 design. One novel feature of the IF strip was the low noise front end using a Peltier cooling system which was rather novel at that time. |
The mechanical design of the scanner (as usual) was in the hands of George Gibson (Head of the Mechanical Lab), known to everyone as 'Gibby' with the canned servo amplifier and mag-amp design including an 'E' pick-off by John Yarrow et al. At the time this was all considered novel and quite unique. The scanner was to be a 2 axis line of sight unit, which in line with the weight saving remit had to be of minimum weight consistent with the need to withstand rigorous vibration and climatic testing. This it did very successfully and it has stood the test of time. |
As can be seen, VJ had much involvement in formulating the overall design approach and getting ARINC specification acceptance to drive the standard for weather radar in the free world and for his outstanding contribution to airline safety and pushing through this ARINC standard VJ was awarded the prestigious American 'Volare' citation. |
It is a credit to this design team that not only was the system produced in such a short time, but the basic design remained in production for some 14 years with very little need to change and the system has stood the test of time - with the Royal Air Force known to be operating a limited number of E190 systems 50 years after the initial design. |
The General Design |
As originally designed, the basic E190 system consisted of 4 modules, namely: (a) The Scanner unit M2210 (b) The Transmitter/Receiver M2211 (c) The Indicator unit M2212 (d) A junction box M2219 |
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The installation was very compact compared to the E120/E160 with all up weight of the equipment starting at 56 Lb representing a considerable improvement over the E160, which weighed almost twice as much. Of course, dependant on what combination the user selected, this weight increased. |
The other major improvement over the E120/E160 equipment was the range improvement since the E190 had a maximum range of 150 Nm with selectable intermediate ranges of 20 Nm and 50 Nm with a 180° degree total scan in azimuth. |
The whole ethos of the E190 was to maximise the advantages that using transistors gave, which not only saved weight and space but also considerably reduced the power consumption. The use of thermionic vales was limited to a few positions in the microwave and power sections where the characteristics of transistors were unsuitable at that time. |
As a result of clever design, the transmitter power was reduced by 6db from 60kW to 15kW, but the resultant decrease in system gain was compensated by the use of a longer transmitted pulse, improved R.F noise factor and higher antenna gain. This reduction in transmitter power not only saved weight, but it also reduced the power input requirements. This together with the power savings afforded by the use of transistors reduced the total power consumption of the equipment to 300 VA – less than ½ that required for the E120/160 60kW system. |
Apart from transistors, the E190 broke new ground for EKCO by using the (at the time) latest multi-pin connectors made by Cannon to (American) MS specifications for connection to the aircraft systems and using PTFE covered wire throughout with the exception of the scanner unit where the moving parts of the scanner unit were wired using silicone covered wire in order to maintain flexibility over the minus 40°C to plus 55°C operating requirement. |
The principal system characteristics resulting from this design was an 'X' band system operating on 9735 Mc/s with a pulse width of 2.2µSec and a PRF (Pulse Repetition Frequency) of 400 c/s (synchronous). The noise factor was 10dB and the antenna gain was 34dB. |
The overall design concept also considered the need by operators to expand the system so all the individual modules were designed with this in mind and as a result the E190 system became extremely adaptable to suit customer needs. |
From concept to showing the system at the 1959 Farnborough Air Show, the time taken in developing the system was just about 1 year, which was a tremendous achievement given that the technology was so new in virtually every area and is a reflection of the 'world class' radar team assembled at EKCO Malmesbury at that time. As Mike Rose, one of the original team members remembers 'it was certainly an exciting time to work with such gifted engineers in an atmosphere free from rivalries where we all pulled together and helped each other out – the team work was superb'. |
Below is the launch advert in Flight International Magazine for September 11th 1959. At the 1959 SBAC Farnborough show where the system was shown to the public for the first time, quite simply it was a greeted with amazement from the competitors and enthusiasm from the airline industry. Little did they know that it was a close run thing to get the set to the show and involved quite a lot of 'burning the midnight oil' however the team succeeded in having a fully functional working set on the stand. |
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Indicator unit M2212 |
The indicator design concept was by VJ and broke new ground in that for the first time in weather radar, it used a rectangular CRT (made by Ferranti) with an in situ moulded in EHT supply cable. The use of this display screen made it possible to mount all the system controls on the lower half and dispense with the conventional separate control unit. The detail design was done by Jack Halsall and his team. |
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Simplicity and flexibility of operation were prime considerations in the design of the indicator unit; the result being that the whole of the time base generation, main IF and video amplifier was included within the indicator unit, thus also making dual indicator operation easy for those clients who wanted this facility since it permitted independent control of time base range and receiver gain control settings. |
A 'first' with this unit was the use of hinged directly wired printed circuit boards without connectors in the lower section of the indicator for the low power transistor circuits thus allowing for easy access in servicing. The power transistors were mounted on a specially designed heat exchanger integral with the rear panel and a small blower circulated air through this heat exchanger thus maintaining a uniform temperature throughout the unit. |
The CRT size was 5 ¼ x 3 ¼ inch high brightness rectangular tube operating at 18KV, which was specially developed for this application to give a maximum display area while occupying a minimum amount of front panel space. The shape permitted the display of the whole 180 degree scan without the loss of range at the larger azimuth angles. |
The high operating voltage of the tube together with a new design of screen phosphor gave an exceptionally brilliant display, which was needed in the high ambient lighting of a cockpit at high altitude. Where specular refraction was an issue (due to indicator position), a specially designed Polaroid hood was available. |
All the operational controls of the equipment were on the front panel below the CRT, thus eliminating the need for a separate control box. This position eliminating some inter-unit cabling. |
This panel had controls as follows:-
Power Switch. This switch in addition to the normal on/off had a function to switch the stabilisation off, which locked the plane of scan to the aircraft axis in the event of a stabilisation reference failure. Contrast Control. This control allowed the flight crew to adjust the contrast to suit ambient light conditions without upsetting the adjustment of interrelated settings such as manual gain and brilliance. Marker Brilliance. This control allowed the flight crew to adjust the brilliance of the markers. Time Base Range Switch. This switch controlled the range position settings, which were 20Nm, 50Nm and 150Nm (note: the corresponding range marker intervals were 5, 10 and 50Nm). In addition this switch had a 'standby function', which put the scanner into a stationary position and the modulator off, but still allowed the equipment to be in a state of instant readiness. Function Switch. This switch was a 4 position switch, which had the following functions. Position 1: Mapping - In this position the beam deflection vanes on the scanner dish were brought into action thus giving a Cosectant squared beam, which was suitable for terrain map painting. Position 2: Manual – In this position a conical beam was radiated with manual gain control retained. This position was used for long range mapping as well as cloud painting. Position 3: Weather – In this position the conical beam remained but the receiver gain was adjusted with time base range, which permitted cloud targets to be displayed at intensity independent of range. Position 4: Contour – In this position the conical beam remained but an iso-echo circuit was brought into operation, which caused the inversion of the signal above an predetermined amplitude producing 'black holes' in the display of cloud targets thus highlighting heavy precipitation, which was usually associated with severe turbulence. Manual Gain Control. This controlled varied the IF gain of the receiver. Tilt Control. This control allowed the flight crew to adjust the tilt angle of the scanner dish (and the radiated beam) over the range of 15° up and 15° down. This function was used when the flight crew needed to either enhance 'ground mapping' or to examine clouds at various altitudes. |
Where dual indicators were in the cockpit, a variation of the unit was available, which had a neon light on the panel to show which indicator had control of the scanner unit. |
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Layout by spitsortie for ekco-electronics.co.uk |