The largest "dish" telescope at the Observatory is 26 metres in diameter. Its curved surface is a mirror which reflects the incoming radio waves to the focal point near the top of the tripod. Here a small antenna collects the radio energy and feeds it to a sensitive radio receiver. The receiver boosts the weak signal which is then sent down a cable to the control building, where it is recorded for later analysis.

The 26-metre telescope is mainly used to receive radio waves of 21 -centimetre wavelength. At any instant, it records the radio emission from an area of sky about the size of the full moon. The telescope can be pointed in any direction above the horizon by motors that drive it around two perpendicular axes, and it can "track" a certain object in the sky as the earth rotates.

It is used for studies of diffuse clouds of hydrogen gas in our galaxy by observing the 21 -centimetre-wavelength radio waves that are emitted by hydrogen atoms. In addition, clouds of interstellar gas that have been heated by newly-formed stars have been investigated. The high temperature of these clouds results in very agitated motions of their atoms and electrons, producing radio emission. Superimposed on this general emission from the hot gas are weak radio signals, at specific wavelengths, from atoms other than hydrogen. Studies of these "trace" elements will provide insight into the composition of gas clouds such as the one out of which the sun and solar system formed.