Editing Cosmic Background Explorer (section)

==== Differential Microwave Radiometers (DMR) ====
The Differential Microwave Radiometer (DMR) investigation uses three differential [[radiometer]]s to map the sky at 31.4, 53, and 90 [[Hertz|GHz]]. The radiometers are distributed around the outer surface of the cryostat. Each radiometer employs a pair of horn antennas viewing at 30° from the spin axis of the spacecraft, measuring the differential temperature between points in the sky separated by 60°. At each frequency, there are two channels for dual-polarization measurements for improved sensitivity and for reliability. Each radiometer is a microwave receiver whose input is switched rapidly between the two horn antennas, obtaining the difference in brightness of two fields of view 7° in diameter located 60° apart and 30° from the axis of the spacecraft. High sensitivity is achieved by temperature stabilization (at 300 K for 31.4 GHz and at 140 K for 53 and 90 GHz), by spacecraft spin, and by the ability to integrate over the entire year. Sensitivity to large-scale anisotropies is about 3E-5 K. The instrument weighs {{cvt|120|kg}}, uses 114 watts, and has a data rate of 500 [[Bit rate|bit/s]].<ref name="Experiment3">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1989-089A-03 |title=Experiment: Differential Microwave Radiometers (DMR) |publisher=NASA |date=28 October 2021 |access-date=27 November 2021}} {{PD-notice}}</ref>