The Stanford Big Dish
A picture of The Dish can be seen in the top left corner of this page.About the Dish
In the foothills behind Stanford University sits a 150-foot (46 meters) diameter radio telescope which has come to be known simply as The Dish. Originally constructed in the 1960's to probe the scattering properties of the Earth's ionosphere, the Dish has been utilized in numerous research pursuits in its 30-plus years of existence. Even before The Dish was constructed, it was recognized that the structure would become a University icon. In the original proposal (dated August, 1958) to construct the antenna at is present site, it is written:
It is proposed that the transmitter and other equipment be housed in a one-story building which would be designed and positioned so as to be relatively inconspicuous. The large parabolic antenna, however, cannot be hidden... It is a more pleasing structure than some of the radio antennas that have been used in the past. It is expected that this large, geometrical structure, used for important scientific research, would become widely known as a Stanford University landmark.
Specifications
The Dish is maintained by SRI International. The specifications for the Dish come courtesy of Mike Cousins (SRI International) and are as follows:
| Antenna type | Parabolic reflector |
| Site | Stanford University Radio Science field site, academic reserve area |
| Horizon | Maximum 3 degrees |
| Diameter | 150 feet (45.7 meters) |
| f/d ratio | 0.42 (focus is 63 feet from surface at center) |
| Surface mesh | 5/8 inch spacing, soft aluminum hex pattern |
| Surface roughness | Approximately 1 inch |
| Gravitational deformation | Approximately 1 inch at edge for minimum to maximum elevation |
| Beamwidth/gain attainable (with appropriate feeds) | @ L-band (1420 MHz): 0.25 degree beamwidth, 35% efficiency, 52 dB |
| @ UHF (400 MHz): 1.0 degree beamwidth, 55% efficiency, 43 dB | |
| @ VHF (150 MHz): 3.0 degree beamwidth, 55% efficiency, 35 dB | |
| Feed arrangement | Prime focus, tripod structure, feed house, tilting feed platform for small apparatus, high power cables |
| Reflector structure | Steel torus ring, aluminum tubular rings and radial trusses, non-homologous, light-weight design |
| Reflector structure weight | 100,000 pounds |
| Total structure weight | 300,000 pounds |
| Motion | Elevation over azimuth, wheel and track, CR-170 rail, steel 4-wheel alidade on 140-foot diameter track for azimuth, rack (bull gear) and pinion spur gears for elevation motion |
| Practical limits | Azimuth 2-turns, elevation 3 to 87 degrees, azimuth cable wrap via central hole and tunnel |
| Programmed tracking speed | 1 degree/second, useful for LEO satellite tracking to elevations of approximately 65 degrees |
| Programmed tracking acceleration | 1 degree/second^2 |
| Motion control | AC vector controlled 25-HP motors giving full torque through entire speed range + to - including 0 with dynamic braking (60-HP capacity) |
| Control computer | PC with appropriate multiple parallel interfaces, programmed in Pascal, code similar to Sondrestromfjord (Greenland) incoherent scatter radar, GPS timing available |
| Positional resolution | 0.01 degrees azimuth and elevation, 1-turn binary optical encoders, unique azimuth encoder offset mechanical connection |