Historical Photo of the Month - April 2007

Earthquake Valley Antenna Test
Photograph Number 331-2547D

The March 2007 Historical Photo of the Month showed a prototype antenna tested near JPL in March 1956. Two months later in Earthquake Valley, San Diego County, similar helical antennas were tested in conjunction with a Microlock receiver. Two objectives of the tests were to gain experience with the Microlock ground station equipment and determine the accuracy of the interferometer antenna system.

Three of the helical antennas were spaced just over 100 feet apart. Two phototheodolites behind the antennas were used to measure the system's angular accuracy. The van at the far left contained the receiver equipment and other instruments. A helicopter towing a transmitting beacon was again used to simulate the signal of a satellite in orbit. It was determined that the system could track a beacon of 1 milliwatt at a distance of about 6,000 miles. The low ambient noise level in Earthquake Valley helped to increase the receiver's performance, compared to the tests done near JPL.

The next step in the development of satellite communications can be seen in the January 2004 Historical Photo. It shows the mobile tracking system used for the Explorer 1, and Pioneer 3 and 4 spacecraft.

[Archival sources: Photo albums and indexes, History Collection document 3-1041.] For more detailed information about the history of JPL, and about the evolution of communication technology, contact the JPL Archives for assistance.