Wednesday, October 08, 2014


In addition to the Navigator system, Decca also designed a special long-range system for crossing the North Atlantic Ocean. It was called DECTRA. They rolled it out in 1957, installing one node in Gander, Newfoundland, and another in Prestwick, Scotland. These operated in pairs, as slave and master stations., with one of each at each end. The radio waves were about a mile long, and the two pairs of stations were almost 100 miles apart on 70 kHz., transmitting alternately, not concurrently.

In an era that spawned a slew of radar systems: Doppler, Roller Map, Hi-fix, Loran C, Decca Navigator, Delrac and Omega, Sea-fix, Mini-fix, Lambda, and Data Link. DECTRA stands out as a very unique system that only operated for a short time.

The system was an adaptation of Decca intended to serve the needs of a very different terrain. The transmissions used normal "pattern" transmitters of a much higher power than on standard DECCA frequencies. The system was strangely simple. It consisted of two RF amplifiers, an oscillator, mixer, divider and phase component. With the two combined signals a navigating vessel can plot a course using phase meter reading.

The name DECTRA was actually an acronym for "DECcca Tracking and RAnging." Between the DECCA system over Europe and DECTRA over the Atlantic  it was said that there existed a continuous aerial highway between London and Quebec. While initially supportive, the UK eventually soured on the multiple competing systems. As late as 1959 they were pushing for adoption of Decca and DECTRA,