Historical Photo of the Month - March 2007

Microlock Ground Antenna, 1956
Photograph Number 331-2426A

On March 22, 1956, preliminary satellite tracking tests began in a field near JPL. The antenna is being assembled in the photo above. The prototype Microlock ground receiving station included the antenna, instrumentation built into a 25 foot van, generators, and other equipment.

This experimental antenna included a ten-foot square groundplane made of plywood and metal, a three-foot diameter by five-foot long fiberglass reinforced plastic tube with a metal strip helix, and two struts in the rear that allow the groundplane to be tilted to any angle. The cylinder detached from the groundplane, which then separated into 3 pieces for transport.

A low-power, light-weight transmitting beacon was towed by a helicopter at about 10,000 feet, simulating the flight of a satellite in the distance and over the test site. A 450-foot nylon rope separated the beacon from the helicopter, to minimize any effects on the experiment. The beacon was similar in size and shape to components used less than two years later on Explorer I.

Next month's Historical Photo will show further tests of tracking stations in Earthquake Valley.

For more detailed information about the history of JPL, and about the evolution of communication technology, contact the JPL Archives for assistance. [Archival sources: Photo albums and indexes, History Collection document 2-746.]