from windblown debris. The positions of the panels can be adjusted from the front of the dish. The initial adjustment of the surface panels in Hawaii was done in the service hangar, using a rotating template. After the antennas were deployed, the surfaces were measured using near-field holography with a 232.4 GHz beacon source mounted on the exterior cat-walk of the Subaru building, 67 meters above the SMA's subcompact pad ring. The panel positions were adjusted based on the holography results, and holography guided adjustments are repeated periodically, to maintain the surface quality. After several rounds of adjustment, the surface's error is typically about 15 microns RMS. Heating units are installed on the primary mirror, the quadrupod supporting the secondary mirror, and the secondary mirror itself, in order to prevent ice formation in high humidity conditions. Each antenna has a cabin holding the electronics needed to control the antenna, as well as the Nasmyth focus receivers. This temperature-controlled cabin nearly encloses the antenna's steel mount to minimize pointing errors due to thermal changes. Receivers The SMA uses cryogenic SIS heterodyne receivers, at a bent Nasmyth focus. All receivers are mounted in a single large cryostat within the antenna cabin. The cryostat can accommodate up to eight receiver inserts, each of which holds a single receiver. A rotating wire grid beam splitter followed by a rotating mirror directs the two linear polarizations of the incoming radiation to two of the receiver inserts. This allows the array to observe either a single polarization of two different frequency bands simultaneously, or both polarizations of a single band simultaneously to improve sensitivity and measure Stokes parameters. Receivers are available to cover frequencies from 194 to 408 GHz, without gaps. However full polarization measurements can only be made around 230 and 345 GHz, where pairs of receivers can be tuned to the same frequency, and quarter wave plates optimized for those frequencies can be inserted into the optical path. The receivers are sensitive to both sidebands produced by the heterodyne mixing. The sidebands are separated by introducing a Walsh pattern of 90 degree phase changes in the LO signal, and demodulating that pattern within the correlator. A Walsh pattern of 180 degree phase changes, unique to each antenna, is also introduced to the LO, in order to suppress cross talk between the IFs arriving at the correlator from different antennas. Thanks to the recent wideband