True Story No4


Hot stuff this computer gear!

A long time ago now it was decided to expand a certain large Defence Contractors' Software Design Department's sphere of interest.

In the early days of integrated circuits and the Cold War there were loads of opportunities for selling bits of kit to NATO.

Combining the marketing function into the said Software Department's responsibility paved the way for near disaster. The Department was able to operate totally independently to the rest of the Company wherein resided experience in matters of particular skills.

When the first of 22 special communications data processing equipments, "vital to the defence of the free world", was sent down an ex-coal mine in Belgium to a NATO Comcen the first of many problems surfaced.

The "programmers" came back from NATO HQ to a heated meeting with senior managers. "We thought that when the specification called for "TEMPEST" it meant something to do with the weather," was the comment by the Project Manager, "But," he said, "We cracked on we knew all along what they meant and said this was just a prototype".

Unfortunately, to the software people, "TEMPEST" had just been a word, and unless you knew about it in those days, it was. Other Departments knew, but of course, because of the new way of operating, THEY hadn't found out about the "Message Heading Generator" until too late.

"TEMPEST" is the expression used by the "cloak and dagger" agencies to cover the specification of an equipment's electro-magnetic radiation and signal leakage. In order to meet TEMPEST requirements the equipment must not emit any radiation or conduct anything to its output which may impart to a listening third party any useful intelligence. For example if one was to park one's car in a busy commercial street and operate a suitable television receiver conected to a high gain directional aerial one could view information being displayed on a nearby computer screen. Commercial equipment will radiate all sorts of noise, some of which can be resolved, by an expert, into information. Military equipment used for sensitive applications must not be allowed to radiate information to all and sundry. The maximum levels of radiation and conduction permitted for these equipments is covered by TEMPEST.

Inexperienced electrical and mechanical designers had been roped in to help out the programmers in what was seen as a piece of software in a tin box.

After spending loads of money it eventually got sorted out and 22 equipments were delivered all over Europe. Soon however we got reports of failures. The MHG design engineer helped out and new components were fitted. These failed in turn and such was the standing of the Defence Contractor that the failures were automatically attributed to the component supplier.

Still failures occurred. Eventually, when all 22 failed equipments had been returned to the factory, Allan was asked to look into the problem and find a new supplier for the rogue component with an "abysmal MTBF".

Each of the eight communications interfaces was made of discrete components including an enormous stud-mounted 80 volt zener diode. When an interface wasn't being used its zener diode dissipated loads of power and went close to melt-down. In the chill of our laboratory they survived…just. When in a nice warm Comcen they didn't.

Looking at the manufacturer's curves, rather than the optimistic max power in watts on an infinite heatsink at the North Pole, the poor zeners, with no heatsinks, were operating miles outside their spec., and at times their junction temperatures must have been close to the temperature of the sun!
Because of the threat of having to re-test, I had to work out a solution which used the original circuit board, the same circuit track, as many original components as possible AND wasn't obvious to the customer AND allowed shortcomings to rest with the zener supplier. I did, it worked, and our reputation emerged spotless.

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