Introduction

As part of the work for the ROTOR contract the decision was made to develop a fixed-coil design for the GCI stations. The engineering work on the fixed-coil display - Console Type 64 - and its radar office equipment was done at Great Baddow.

The fixed-coil display work was an important milestone, in that it established a display and data-handling laboratory that served Marconi for a quarter of a century and a pattern of engineering that led to products that were reliable and suitable for quantity manufacture. The fixed coil development started in 1950, aiming at completion in 1953. A large team of engineers, some graduates and some with practical Service experience, was set up and dedicated facilities for making prototypes were put in place. The development programme, like all large `crash' programmes breaking new ground, suffered a few problems. There were some difficulties with the tube, which was virtually being chosen by the Ministry, from alternatives that were in fact physically and dimensionally different, in parallel with the main development. None the less, production went ahead in a time scale that was appropriate for the whole project. The first 1000 or so  complete Type  64 consoles and several thousand items of radar office equipment were manufactured by subcontract in the Plessey Company as a result of a very close collaboration. Later, there was retrospective fitting to other stations such as the CEW, together with new stations, and these were produced in Chelmsford.

Photographs

(The coloured photographs are taken at the RAF Signals Museum, Henlow - click thumbnail for a larger version)

R3 Intercept Cabin	Indicator Unit
Console 64	Showing LH and RH Deflection Amps & Voltage Stabiliser

Extract from article by Roy Simons

In 1950 it was decided that the displays for the GCFs should be 'fixed coil’ which would enable markers to be displayed. These displays would use a 'new' fluoride CRT that would give better track presentation than the existing green or blue phosphor tubes. This decision resulted in a major development programme at Baddow to attempt to design and produce a new display with all its radar office equipment to meet the original time scale of the end of 1953 for completion of ROTOR 1. In fact all the CEW and CHEL sites were completed by April 1953. The first GCI at Bawdsey was ready in December 1953.

In order to implement the 'Fixed Coil' display work a large number of engineers were recruited to supplement the existing radar people. Many of these had wartime experience, but about an equal number were new graduates. Rooms 123a, 123b, 124, 101, 102, 103 at Baddow were made available. A special workshop team was allocated to ROTOR prototyping under Fred Leach and a complete radar office was erected with all its cooling plant in Room 123a and three displays in Room 103.

Maurice Cuffiin was initially the project manager for the radar office and I was the project manager for the display. Cufflin left after a short period to join EMI and I became responsible for all the equipment design and its transfer to Plessey in a new factory in Horns Road Ilford, to where the manufacture was subcontracted. 

It was proposed that a liaison visit should be made to ASE Witley as it was believed that they were designing a display system to work with the 984 and it was probable that it might have similar requirements to ours. As a result of a full day's visit, the only information we received was a drawing of a diode with nothing connected to either end and the surprising knowledge that ASE were using the EEV metal coned CRT in their work.  

There were many reasons why the delivery of the first 'fixed coil' system was later than the hopes of the Ministry. The basic idea came from TRE, where an experimental data handling system was being studied using electromechanical storage from Ericcson. This became known as ADIS and the prototype was installed in H Block, well before the Blue Yeoman was added.

Originally the deflection waveforms were to be resolved using sine-cosine, as this gave a DC reference from input to output and would allow any markers to be easily referenced in position. However no wire-based resolver was capable of giving the smoothness and accuracy required, not to mention problems with contact noise. In the event, the sine cosine resolvers were retained for the height finding azimuth resolvers to present a short intertrace azimuth mark on the displays and a decision was  taken to use a magslip resolver for the PPIs.

This decision required the design of accurate clamps for the intertrace periods and precise linear amplifiers. One or two issues had to be solved. Diodes had significant heater to cathode leakage, causing AC modulation of the clamped position. This was cured by having separate heater transformers. The rotating armature of the magslip generated an AC current, which was not earthed reliably via the ball races at each end, causing noise. This was solved by adding a brush to remove the unwanted noise signals. Capacitors with a large dielectric constant were shown to have storage in the dielectric, solved by using a mica dielectric where needed.

Uncertainty or incorrect decisions were taken by the Ministry on some items which caused significant delay. The new CRT, the CV429, was initially made with various bulb shapes by several firms. There were also several contracts all starting to use this tube: Orange Yeoman, 984, PAR and our Type 64. At the meeting which I attended, the decision as to which shape should be used was determined by the Ministry looking to the system which was closest to production. At that time PAR! This determined the shape, which was that supplied by EMI. We had been using tubes with the Cinema Television bulb shape. When the specification was finalised we had a major redesign to cope with a much bulkier glass envelope.

This was not the end of the tube story. Mullard, who were convinced that they would get the contract, had proceeded to go firm on their glass shape and went into production. They did get the contract, (you could have expected it to have gone to EMI as their tube had the chosen shape) but, no, it was awarded to Mullard. Unfortunately the Mullard bulb shape did not conform to the Ministry drawings and they were not prepared to alter their production tools. They sub-contracted the manufacture to Cinema Television, which firm the Ministry had excluded from their consideration as the process control at the Rotunda was so poor that there was cross contamination between phosphors, which gave a white or green flash in front of the orange fluoride which was or should be without any initial flash.

Another decision, which caused considerable delay, was the requirement to reduce the width of the display console by one inch after the design was well advanced and initial models had been built. Almost every unit had to be redesigned, wrapping some round the now larger tube housing and reducing accessibility considerably.

A by-product of the choice of the EMI tube was the effect on the focusing arrangements. We had carried out a detailed analysis of the path of the beam through long focus coils using specially made one inch CRT's which could have the screen positioned at any point within the coil and a very good performance coil was designed and built into the prototypes. However the EMI tube had a very long gun assembly which reached almost up to the join with the bulb. This caused us to have to change to a narrow gap coil as used in domestic TV to avoid interaction between the metal of the gun and the magnetic field of the focus coil.

Another problem arose when we first put live radar on to the display. With the fixed coil system, off-centering to the full range of the picture was easily available. However, with the clutter off centred into the neck of the tube there was sufficient energy in the beam to puncture the glass. This caused a late extra development and incorporation of an octagonal blanking unit to prevent this happening by restricting the video pedestal to the area of the tube face.

Console 64 at the RAF Signals Museum at Henlow

Henlow have some of the equipment formerly at RAF Locking - the museum website includes a description of the Console 64 fixed-coil display system and details of the refurbishment of a Console 64 and associated drive equipment. Also available are copies of the APs (Air Ministry Publications) for the Console 64 and fixed coil back-up. In addition there is a video of the heightfinder being azicated by a joystick provided by Colin Hinson. These are training notes.

Editors note - it seems likely that this equipment is that I had in my charge when I was an instructor at Locking.