The Speech Scrambler: the invention of secure mobile networks
In 1992, a secure mobile phone system came into service for the first time, when the Thames Valley Police started using a new ‘speech scrambler’ system, following research directed by Professor Joe McGeehan at the University of Bristol Centre for Communications Research. Until this time, unauthorised listeners could scan mobile and fixed telephone calls - eavesdropping the police and posing a threat to their safety and operational effectiveness.
The scrambler started a new era of higher police security, and the encryption techniques involved allowed for the massive expansion of commercial and personal mobile phone usage we see today.
Early improvements to mobile radio
In 1975, Prof McGeehan began research to manipulate the spectrum of received mobile radio signals so they would reach the recipient without fading or loss of quality. By 1980, this work resulted in an improved AM transportable mobile radio, which was adopted by the Securicor fleet of vans, significantly reducing their operational costs.
However, there were still problems with the privacy and security of calls made from analogue phones, which especially concerned the police and, in the late eighties, the Home Office called for competitive trials to be undertaken to research a variety of speech scrambler systems. Prof McGeehan and his team conducted research in response, and their prototype was then developed by GEC-Marconi Secure Systems into the Marconi Advanced Scrambler (MASC) system. The Home Office selected MASC as the recommended speech scrambler for UK police forces, out of five options.
The Speech Scrambler
By 1992, the police were using the scrambler in active service. The new mobile device was no more than a couple of inches in length and could be incorporated into the officer’s uniform radio.
Prof McGeehan recalls: “I spotted that existing technology, with the addition of new novel engineering solutions, could provide the answer. Then, as now, the challenge was to find a commercial partner willing to take a risk, and support the work and its commercial exploitation.”
Although Terrestrial Trunked Radio (TETRA) digital radio has taken over today’s mobile communications, the speech scrambler allowed police forces to convert to digital gradually, as costs came down.