Transmitter Parts Salvaged from Alaska

The observatory's 430 MHz transmitter dates back to the late 1950s, when the BMEWS (Ballistic Missile Warning System) was being designed. Our system, designed at the same time, uses the same type power klystrons.. We lose a klystron about once a year and used to buy replacements from the manufacturer, Litton Industries, at a cost of about $220,000 each (in today's dollars). Around 1986, the BMEWS station at Thule (Greenland) was upgraded to a phased-array radar, and the Air Force gave us 16 surplus tubes. Just as we used up the last of those tubes, the Air Force finished the phased array at BMEWS site 2 in Clear, Alaska. This time we were given 14 tubes. In January Victor Iguina and Jose' Vives went to the base at Clear, where they removed the tubes from the transmitters and prepared them for shipment. The tubes are now on site in Arecibo. In July, accompanied by Jon Hagen, they returned to Clear and filled a 20ft container with waveguide components, two driver klystrons, focusing magnets, vac-ion pump controllers, and other miscellaneous transmitter hardware.

The radar at Clear, off the air for more than a year, was still 95% intact. Miles of WR2100 waveguide connect the three large search antennas (each covering a 40-degree sector) to the two transmitter buildings.	Each search antenna used a fixed parabolic torus reflector, 165 ft high by 400 ft wide. The feeds in front of these reflectors rotated about a vertical axis in order to scan in azimuth. Horizontal cuts through the reflectors are therefore circular arcs, centered on the axis of the scanner. Feeds were provided for beams at two elevation angles, 3.5 degrees and 7 degrees. A missile would be seen as it passed through the lower beam, and then again as it passed through the upper beam. Once detected, the target would handed over to a tracking radar that used a fast- moving 85 ft dish. Each search antenna actually had two fixed horizontal rows of feeds, each with 100 side-by-side horns. Waveguides from each row of horns were routed to enormous rotating distributors ("organ pipe scanners") whose circumferences were about equal to the width of the row of horns. The two transmitter buildings together housed about 25 transmitters. Each transmitter was very similar to our Arecibo transmitter, using two klystrons in parallel. A mile- long access tunnel connected the transmitter buildings and then led to the coal-fired power plant. Receivers used parametric amplifiers with X-band pumps. Three of these BMEWS systems (Thule, Clear, and Fylingdales in England) were built at a cost of more than a billion (1960) dollars.