On Wed, 5 Jan 2005 12:15:33 -0800, Joel Kolstad wrote:
Hi guys,

I saw the Australian movie, "The Dish" over the holidays. It's about the
Parkes Observatory and the large dish antenna used to relay video, audio,
and telemetry feeds from Apollo 11 in 1969 back to NASA.

At one point in the movie, they lose track of where Apollo 11 is and have to
scramble to manually point the dish to get a signal again. However, once
they DO manage to get a signal, they flip a switch and the dish continues to
automatically track Apollo 11.

I'm curious... how is this down?

By counting on the gulibility and limited education of movie audiences. :-)

3 or 4 slightly offset (from the dish's
central feedpoint) receivers, the outputs of which are compared to determine
which way the transmitting source is 'drifting' (then feed back to the
motion control system to move the dish that way)? Or is there a simpler
means?

The way a Hughes Radar system I once worked on did it was to spin the
horn in the dish focal point. The horn was E V E R S O S L I G H T L Y
off center in its axial alignment. The receive signal strength was
constantly compared against a servo feedback from the horn assy. to
determine which way (what angle) the signal source was drifting.

In a system that was polarization sensitive, I guess one could "joggle"
the position of the horn assy. and achieve much the same results.

HNY
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
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