carma, and the carma wvr effort
DESCRIPTION
WVR workshop Wettzell 2006. CARMA, and the CARMA WVR effort. Alberto Bolatto Associate Research Astronomer U.C. Berkeley Astronomy Radio Astronomy Lab. Dick Plambeck (UCB/RAL), Dave Woody (Caltech), Leslie Looney, Yu-Shao Shiao (UI), Douglas Bock (CARMA). Outline. What is CARMA? - PowerPoint PPT PresentationTRANSCRIPT
CARMA, and the CARMA CARMA, and the CARMA WVR effortWVR effort
Alberto BolattoAlberto BolattoAssociate Research AstronomerAssociate Research Astronomer
U.C. Berkeley AstronomyU.C. Berkeley AstronomyRadio Astronomy LabRadio Astronomy Lab
Dick Plambeck (UCB/RAL), Dave Woody (Caltech), Leslie Looney, Yu-Shao Shiao (UI),
Douglas Bock (CARMA)
WVR workshop WVR workshop Wettzell 2006Wettzell 2006
Outline
• What is CARMA?
• The OVRO experience
• The RAL correlation radiometer
• What next?
+ UChicago SZA 8 3.5-m antennas
Berkeley-Illinois-Maryland array
10 6.1-m diameter antennas
Caltech array 6 10.4-m antennas
CEDAR FLAT
Cedar Flat – elevation 2200m
June 2004August 2005
21 Jul 2004 – lifting off the first reflector
panel adjustmentsurface error determined from holography
before adjustment: 127 μm rms
→ 75% loss at 225 GHz
after adjustment: 28 μm rms
→ 7% loss at 225 GHz
all antennas assembled10 Aug 2005
Comparison with other arrays
CARMA
+ SZASMA IRAM ALMA
elevation 2200 m 4200 2500 5000
antennas 23 8 6 50+
baselines 253 28 15 1225+
diameter 10, 6, 3.5 6 15 12, 7
area 850 m2 226 1060 5600+
max baseline
1900 m 500 m 400 m 14 km
E, D configurations
Now
1.6 km
baselines 8–150 m
1mm beam: 2”
E, D, C configurations
for Winter 2005
1.6 km
baselines 8–350 m
1mm beam: 0.8”
E, D, C, B, B+ configurations
for Winter 2006
1.6 km
baselines 8–1700 m
1mm beam: 0.2”
E, D, C, B, A configurations
for Winter 2008
1.6 km
baselines 8–1900 m
1mm beam: 0.13”
225 GHz zenith opacity
% tau mm H2O
SSB Tsys
25 <.12 <1.8 <290
50 <.16 <2.4 <350
75 <.28 <4.3 <520
Tsys computed for 1.5 airmasses, Trcvr(DSB) = 45 K
OVRO WVR
Sample phase improvement
It can work, but…
• Can it work reliably?
• It’s easy to improve very bad tracks, but good tracks can be worsen
• Only works for ~40% of the dataY.-S. Shiao et al., SPIE, (2006)
Correlation WVR at 22 GHz
• Correlation receiver: less sensitive to amplifier gain variations, no moving parts, built-in absolute calibration. Fast control of temperature of reference for nulling: ultimate stability.
• Weak points: complexity, sensitive to spurious correlations
Expected performance
• Measured amplifier performance based on Hittite commercial HMC 281 GaAs mmic ($40):
Tnoise ~55 K, G ~23 dB, BP ~16-36 GHz • Expect Tsys ~ 140 K, or RMS ~5 mK in 1s in 1 GHz
hot spill~3% (9 K), input w.g. loss~0.5 dB (32 K), hybrid+w.g./coax loss~0.3 dB (4 K), 2nd amp stage~5-10 K
• Assuming canonical ~4.5 mm/K @ 22.2 GHz expect path RMS ~20 mm in 1s
• Performance will be degraded by control of load temperature, thermometry, spectral baseline removal, etc, but there is a safe margin /20 goal is ~60 mm
Block diagram
x2
CARMA X-band
CTL
CANbus uP + DAQ
22 GHz optics
180 hybrid/magic T
BIMA dewar
HMC 281 cryo amps
DITOM D3I1826DUAL HMC281
NARDA 4017C-10
MARKI M1R-0726L
18-26 GHz
ASTRONOMY IF
MCL SLP-550
NARDA 4317B-2D0612LA
9-13.5 GHz YIG OSC.
DETECTOR
4-q multiplier
180° PHASE SWITCH
WR42 th. gap + window
12 K stage
40 K stage
The ReceiverK band
cryo amp (x4)
Controled temp. load
Magic-tee
hybrid
Thermal clamp to 12
K stage
Input (to
horn)
Input (to
horn)
K band cryo amp
(x4)
Thermal clamp to 12
K stageControled temp. load
Magic-tee
hybrid
The Controlled Temperature Load
Cernox sensor chip on top of inverted 50 Ω
alumina resistor
10 mil 50 Ω quartz μstrip
Heater biasing
wire
• Load + sensor mass is 3 mg: fast temperature response
• Once mounted, sensors are calibrated against standards
•S11~-20 dB
Brass pedestal
The Amplifiers
HittiteHMC 281
12 amps put together by Dusty Madison, a freshman summer
student who learned to assemble and wirebond them
The Dewar “Insert”
• Minimum impact on existing BIMA dewar
• No internal screws/electrical connections: just plugs in
• Special 2-port test dewar designed and fabricated
Other HardwareLO/
downconverter
LO/downconverter
IF/MultiplierIF/Multiplier
MicrocontrollerMicrocontroller Signal conditioning
Signal conditioning
The Complete SystemWVR
dewar “inserts”
LO chain and downconvert
er
IF chain, AGC,
multiplier, phase
switching, and filters
Signal conditionin
g and control
electronics
XAC uP, ADC, DAC,
and CANbus
Nice idea, but it has proven difficult to make it work
• Tests looking into heated cryogenic waveguide load in 2nd dewar
• Non flat passband– Slope is caused by
imperfect hybrid– Central feature is
from CTL wg adaptor
– Edges not quite understood
– A few K of “extra” correlation, probably reflections in hybrid
Status May 2005Status May 2005
Nice idea, but it has proven difficult to make it work
• Spurious correlation due to internal coherent reflections– Could be mitigated
with input isolators
• Even without moving parts, calibration is not repeatable enough– Difficult to attain the
mK calibrability goal
• Further work?
Status May 2005Status May 2005
What next?• Revert to basics – Simple is beautiful• Implement a Dicke-switch radiometer
– Room temperature: use noise diode– Cryogenic: use controlled temperature load
LOCTL
DETe.g. AD8309
Dicke-WVR assembly using CTL
Conclusions• Phase correction schemes improve correlation
for a fraction of the tracks, but not all the time. Atmosphere or engineering?
• Nulling correlation radiometers are nice in theory, very difficult in practice. Large part count and complexity makes them unattractive for (university based) interferometers.
• Dickey-switch type schemes are considerably simpler, and more attractive if stability of 1:10,000 can be attained. Partial successes at PdBI, VLA, and ALMA/SMA suggest they are viable.