The DENEL Overberg Test Range, DENEL OTR is a large aerospace test facility on the south coast of South Africa. There are three large monopulse tracking radars, two smaller tracking radars and a number of optical trackers.

The three large monopulse tracking radars were originally controlled by Gould-SEL computers with embedded CSPI MAP array processors. The array processors had become un-maintainable, and the old Gould-SEL operating system and non-standard Fortran dialect hampered software development. The project was to replace the Gould-SEL and array processor systems with PCs running modern and maintainable codes. There were four important contraints:

• The radars were to remain operational throughout the project. OTR has a busy test schedule, and no system was to be rendered inoperable at any time.

• The system performance was required to be at least as good as that of the original Gould-SEL systems.

• The safety of the systems was not to be compromised. The radars have large moving parts, sensitive receivers and high voltage transmitters. The original software had safety interlocks to protect the equipment and these were to be preserved and extended.

• The code was to be migrated and sometimes re-implemented in languages appropriate to the sub-systems. Therefore the signal processing remained in Fortran, the instrument control was largely converted to C and the user interfaces to C++.

The project was divided broadly into four phases, though there was overlap between tha last two.

• The CSPI MAP array processors were replaced by PCs running a Fortran emulation of the array processor code. The PCs communicated with the Gould-SEL system through HSD devices. Some of the CSPI MAP codes were successfully analysed and were replaced by new Fortran routines. Parts of the array processor code were judged to be too obscure to be analysed and an automatic translator was written to convert these to Fortran.

• The data recording system in the Gould-SEL host was then replaced by PC code. This involved the translation of the Gould-SEL real numbers into IEEE format, and decoding of the data structures used in the original programs.

• The complete signal processing was then transferred to the PC. This required replacement of the Gould-SEL DATAPOOL and shared memory constructs.

• The instrument control and user interfaces were then re-implemented on a PC cluster.

The main project was completed and accepted in 2013. The completion is described here.

However, there are ongoing projects to upgrade parts of the system hardware and software.

Many staff were involved in the project, in particular, the radar managers Stephen Day Mandy and Justin Abraham, the software team, Harry Huyzers, Fred Arnott, Ian Swart, Thomas Bennett (Now at SKA), Brian Farrimond (SimCon) and John Collins (SimCon), the hardware engineers, Wimpie van der Westhuizen and Gerard van Eck, and the radar operators, Louis van der Walt, Cassie Carstens, Jeff Owens, Julie Meswatu (Now at SALT) and Berto Botha.