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National Aeronautics and Space Administration

Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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ARCADE Radiometers

ARCADE consists of a set of seven Dicke-switched cryogenic radiometers covering the poorly-measured centimeter band between full-sky surveys at radio frequencies (f < 3 GHz) and the FIRAS millimeter and sub-mm measurements (f > 60 GHz).

Block Diagram
Each radiometer consists of a cryogenic front end with a high electron mobility transistor (HEMT) amplifier, switched at 75 Hz for gain stability between a wavelength-scaled corrugated conical horn antenna and a temperature-controlled internal load. Latching ferrite switches alternately connect the amplifier input to the sky horn or an internal reference load. The radiometer back ends are housed in a temperature-controlled module mounted outside the dewar, with stainless steel waveguide (30 GHz and above) or coax (10 GHz and below) providing the RF link between the cryogenic and room-temperature components. The back end of each radiometer is split into two frequency sub-channels: one covering the lower half of the front-end passband and an independent channel covering the upper half of the front-end passband. Video preamplifiers following each detector diode separately amplify the dc and ac portions of the signal, proportional to the total power on the diode and the antenna-load temperature difference, respectively. A lockin amplifier demodulates the switched (ac) signal and integrates for 0.5 second to produce an output proportional to the difference in power between the antenna and the internal load. The lockin output and total power signals are digitized at 2 Hz and written to an on-board recorder before being telemetered to the ground.

Radiometer Collection 5 GHz radiometer back end
Would you buy a radiometer from this man?
5 GHz radiometer back end

The table below summarizes the ARCADE radiometers.

ARCADE Receiver Summary

3 GHz 5 GHz 7 GHz 10 GHz 30 GHz* 90 GHz
Lower Freq (GHz) 3.1 5.2 7.8 9.5 28.5 87.5
Upper Freq (GHz) 3.5 5.8 8.5 10.7 31.5 90.5
Cold Stage Gain (dB) 40 29 40 40 25 26
System Temperature (K) 7 8 13 12 40 60
Sensitivity ( mK Sqrt(s) ) 0.7 0.7 1.0 0.7 1.5 2.2

* There are 2 independent radiometers at 30 GHz: one with beam FWHM 12 degrees and a second identical radiometer with beam FWHM 4 degrees. All other radiometers have FWHM of 12 degrees.