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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).
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.
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Would you buy a radiometer from this man?
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5 GHz radiometer back end
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The table below summarizes the ARCADE radiometers.
ARCADE Receiver Summary
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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.
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