The K6QXY-K6MXI EME Array details


In the K6QXY-K6MXI eme array, the tower axle assembly consists of 60 ft of Rohn 45G tower. One end of the axle is supported by a trunion attached to a modified Glen Martin "Hazer 4" assembly that is raised and lowered, while riding on 70 feet of Rohn 25G tower. Approximately 30 feet of vertical travel allows the axle to be positioned in elevation from about 35 to 65 degrees. The vertical travel, up and down, of the Rohn 45G, is accomplished by using an ac powered cable winch capable of lifting in excess of 2000 pounds. A very high gear ratio allows the winch to maintain a specific elevation without the need for any locking mechanism. The lower end of the axle is also supported by a trunion attached to a cart assemnbly riding on parallel tracks. A series of 10,000 pound bearings and 2" diameter drill rod shafts allow for rotation of the axial antenna support structure. Plates were custom made to accept the axial bearings mounted inside the Rohn tower sections.

The entire axle can be positioned in azimuth +/- 30 degrees in 10 degree increments. The vertical tower is guyed three ways above and below the length traversed by the Hazer. Because of other existing towers at the site, one guy anchor required elevation. A 3" X 20 ft section of galvanized pipe was used to accomplish this task.

The axle assembly is aligned on 120 degrees "true" azimuth. A digital theodolite enabled the layout. For K6QXY's latitude and longitude in California, this 120 degree line corresponds to the UNIVERSAL EME WINDOW for the United States and Europe. The window corresponds to a meridian crossing near the middle of the North American continent, and a moonset in Central Europe. The window includes the region of maximum northerly Lunar declination. Since the moon changes declination in a sinusoidal fashion, it remains near maximum declination for several days. This optimizes the number of moon-days per month.

The array antennas are Directive Systems DS50-5 yagis. They are stacked at 16 X 16 feet on the Rohn 45 axle. They are mounted vertically polarized near their reflectors to maximize ground clearance, and reduce phasing harness length. The "E" and "H" plane beamwidths are 25 degrees and 12.5 degrees respectively. Forward gain is calculated to be approximately 18.6 dBd. The antennas are fed with phase matched Times Microwave LMR-400 coax, and combined with two and four port air power dividers. The rotation loop is made of Times LMR-600 coax to a main feeder of 1 5/8" Heliax.

This combination of some limited elevation and azimuth steering allows this array to see moon set from Northern Africa through Europe for 7-10 days per month.