The ‘XR1’ is a satellite navigation receiver made circa 1983 by Polytechnic Marine. The XR1 works with the Global Positioning System (GPS), a satellite-based navigation system owned by the United States government, to determine a user’s latitude and longitude. A research and development team in Daventry, UK developed this experimental model from 1980 and it went into production from 1983 to 1987. GPS provides geolocation and time information to a GPS receiver anywhere on Earth where there is an unobstructed sight to four or more GPS satellites.

The single-channel GPS L1 C/A receiver tracked one satellite at a time using a slow sequencing algorithm. It dwelled on each satellite around 1 second. Inputs for Dead Reckoning devices (compass and log) for periods of no satellite coverage. It has 8 digital boards with 5 um custom chips, RF board and power supply. It needed several processors to acquire and track and compute position fix.
In 1987, there were only five satellites out of the minimum 24 required to make a full operational constellation. This meant that the XR1 only worked for a few hours a day when at least four of the satellites came together to be visible above the horizon. The XR1 thus worked best at a fixed point rather than on a moving ship.
The original cost price (£50,000) made it an expensive instrument for the time. It was purchased by universities, British and American military forces, and by the UK off-shore oil industry—it was a value tool for rig positioning in the North Sea. In 1983, Polytechnic Marine Ltd received a Queen’s Award for technological achievement in Transit satellite navigation receivers. This XR1 is 19” rack mounted.