About the North Atlantic Radio System

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As the Dew Line extended eastward, across Greenland, then (although the sites weren't officially part of the Dew Line) to US sites in Iceland, a Danish site in the Faroes, and British sites in Scotland and England, the method of communication chosen, as on the Dew Line, was Tropospheric Scatter (Tropo.) Tropo relies on relatively high-powered transmitters and large high-gain "billboard" antennas to "bounce"* signals off of particles in the troposphere, the lowest layer of the atmosphere. Depending on the power used, and the antenna sizes, a single tropospheric "hop" can span several hundred miles, which would require several repeaters, if ordinary microwave systems were used. 

Beginning in 1960 and 1961, five Tropo sites were constructed.  Site 41, at Keflavík, served the USAF radar at "Rockville" in southwest Iceland and Site 42 was co-located with the USAF radar at Höfn, in southeast Iceland.  NATO Comm Unit was manned jointly by US and Danish technicians and was located with the Royal Danish Air Force radar near Tórshavn in the Faroe Islands.  There were two sites in the UK; one at Mormond Hill, Scotland, serving the Royal Air Force Buchan radar and the other at Fylingdales Moor in northern England to provide connectivity for the Ballistic Missile Early Warning System (BMEWS) site operated by the RAF.

Except for Fylingdales, which was originally at the end of the "chain,"  the NARS sites were all laid out in a similar manner.  There was a "Composite" building, which contained one of the radio links and the multiplexers and other terminal equipment necessary for local telephone and teletype distribution.  The site's power plant, offices and other facilities were also located in the Composite building.  The other radio link was located in a smaller "Radio" building, located anywhere from a few feet to a hundred yards from the Composite building.  The buildings at Mormond Hill (which had a separate power building) and NATO Comm were linked by enclosed walkways.  The two Iceland sites had no such luxury, which made for some interesting trips during blizzard conditions.

The Tropo equipment used on the NARS sites was the AN/FRC-39A(V), manufactured by Radio Engineering Laboratories.  These radios could be configured, by the use of different power amplifier combinations, for transmission at 1, 10 or 50kW.  With the exception of both links at Site 41, and Site 42's link to Site 41, which were 50 kW, the NARS sites used the 10kW version.  There were two transmitters and four receivers, each of which was (theoretically) capable of operation at signal levels as low as -105 dBm, with the optional "threshold extenders" installed and properly maintained.  Because the equipment used vacuum-tube technology, maintenance was a constant problem.  While the radios were fairly reliable, they were difficult to maintain, to the manufacturer's specifications, for any length of time, and many thousands of hours were expended "tweaking" them back into spec.

The quality of tropo communications depends upon many factors and can vary from one hour to the next. By the mid-1970s, serious questions were being raised about the ability of the NARS system to carry the sort of communications that it had been designed for.    Circuits were frequently logged out, especially during the winter, due to high noise levels.  This was before the days of high-speed data transmission but even the simplest teletype circuit would not function and, at times, it was difficult to even have a telephone conversation.  Matters slowly began to improve, with the implementation of new maintenance procedures that, in many cases, far exceeded what was called for by either the manufacturer or the Air Force. Beginning about 1978, the tube equipment began to be replaced with its solid-state counterparts and, eventually, maintenance became easier as the overall transmission quality steadily improved.  At the time of closure, in 1992, it was usually possible to pass data at speeds up to 9.6kbps.

The demise of the NARS system was not unexpected.  As satellite communications became more prevalent, it was obvious that Tropospheric Scatter would soon be a thing of the past.  In 1988, one of the Dew Line sites in Greenland, Dye-2, was declared unsafe and was abandoned.  Since most of the NARS circuits back to the US passed through Dye-2, it was only a matter of time before NARS would be closed down.  Then, in 1989, it was announced that Site 46, at Fylingdales, England, would have to be closed to make way for the new BMEWS facility that was being planned.  Site 46 ceased operation in 1990, and was dismantled, leaving only the empty building.  The following year, the decision was finally made to close down all the NARS sites by 1992, thus ending over 30 years of service to the US Air Force.

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