Transcript Hardware Performance Rick Perley

Hardware Performance
Rick Perley
With much essential help from Barry Clark, Ken Sowinski,
Vivek Dhwan, Walter Brisken, George Moellenbrock, Bob
Hayward, Dan Merteley, and many others.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
1
Requirements
• The Project Book has listed in detail the
antenna and array performance
requirements needed to meet the scientific
requirements.
• In this talk, I will review progress in
meeting the key performance requirements.
• Not all items can be tested yet – most
outstanding ones are limited by basic
reliability issues.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
2
EVLA Testing Team
• The (unofficial) testing team:
– Ken Sowinski, Rick Perley, Barry Clark, Vivek
Dhawan, Walter Brisken, George Moellenbrock.
• A very intensive process – tests done daily, results
back to engineers/programmers within hours.
• An amazing range of problems uncovered and
repaired.
– Neither time nor space to describe.
• We believe we are ‘over the hump’ in tracking
down reliability and performance issues.
• Undoubtedly some remaining subtle problems.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
3
Antenna-Mechanical
• Requirements essentially match current best
performance of VLA antennas.
• Pointing: 6” blind, 2 – 3” referenced.
• Status: EVLA antenna pointing problems now
rectified, referenced pointing now enabled.
• More data needed, but we are close to meeting this
requirement.
• `Super-Sidereal Tracking’ for `On-The-Fly’
imaging not implemented. Awaits identification of
necessary funding.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
4
Antenna-Efficiency
• Table shows
requirements and
status.
• Observations made
on known standards
calibrated with
hot/cold loads.
• We are on track to
meet all
requirements.
Band
L
Req.
.45
Obs.
.43 - .5
S
C
X
.62
.60
.56
TBD
.55 - .65
TBD
U
K
A
.54
.51
.39
TBD
.48 - .56
TBD
Q
.34
.26 - .29*
* Observations made without optimal focus or
subreflector position. Further holography required.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
5
Antenna Polarization
• Linear: Requirements set to give < 5% crosspolarization response, stable to < 1% over 12
hours.
– C-Band: Easily meets specs at 4850 MHz, but we are
using VLBA-style polarizer. We await the new
OMT/Hybrid combination.
– L-Band: Have new hybrid, but with old VLA OMT.
Results are encouraging (following slides).
– K, Q Bands: Using existing systems. No problems
found nor expected.
• Circular: Set by beam squint – no change from
VLA expected. Measurements to follow.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
6
L-Band Polarization
(George Moellenbrock)
• Recent sky tests
(Red) show
acceptable cross
polarization.
• Spike at 1450
MHz due to
trapped modes in
VLA OMT
• Blue lines show
predicted
polarization from
lab measurements.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
7
More Polarization
• Antennas 13 x 16
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
8
Receiver Tsys
• System Temperature:
Results in Table.
• All measurements
made with hot/cold
load calibration, at
output of FE or IF on
the antenna.
• Requirements are met,
esp. at high
frequencies.
Rick Perley
Band
Req.
Obs.
L
S
C
X
27
27
27
31
28
TBD
24
TBD
U
K
A
38
61
55
TBD
45
TBD
Q
70
65
EVLA Advisory Committee Meeting
May 8-9, 2006
9
Gain Linearity/Stability
• Tsys monitoring requirement of 0.5% accuracy.
– Needed to compute visibility amplitude from
correlation coefficient.
• No specific requirement on temporal stability.
• On-sky observations show (short-term) amplitude
stability as good as VLA – at the required level.
• Some issues of stability of Tsys monitoring
remain. Occasional deviations observed, cause as
yet unknown.
• Long-term (many hours) stability TBD – weather
data and round-trip phase not yet implemented.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
10
Phase Stability
(Vivek Dhawan)
• R-T phase correction system better than VLA’s.
• Detailed tests ongoing, and results are
encouraging.
• R-T phase correction not yet turned on. Short-term
phase stability issues have been identified and
(largely) corrected.
• Observed (short-term) phase as good as VLA
antennas.
• Phase change on frequency change noted – cause
understood, and (firmware) fix to be tested.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
11
Bandpass Stability
• A very difficult spec has been set: 0.01%
amplitude, and 0.007 deg phase stability, on
– Timescales less than 1 hour, and
– Frequency scales less than 0.1% of observing
frequency.
• Recent observations of 3C84 at X-band
show we’re close – and probably limited by
VLA base-band hardware.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
12
VLA Amplitude
Differential Hourly Snapshots
• VLA antenna 17
amplitude.
• Ripple due to
waveguide
reflections.
• Magnitude ~ 0.5%
• Typical for all
VLA antennas.
RCP
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
LCP
13
VLA Phase
• Showing VLA
ripple in phase.
• Magnitude ~ 0.5
degrees.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
14
EVLA Antenna 18
Amplitude Results
• Amplitude stability
excellent.
• No sign of VLA’s 3 MHz
ripple.
• Full range is 0.4%.
• Away from baseband
edge, range is ~.05%.
• Variation likely due to
VLA baseband filter.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
15
EVLA Antenna 18
Phase
• Hourly observations of
bandpass at X-band.
• Mean bandpass removed.
• BW is ~10 MHz
• Phase peak range 0.2
degrees.
• Away from baseband
edge, phase range is 0.04
degrees.
• Instability origin unclear,
but unlikely to be FE.
RCP
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
LCP
16
Headroom/Solar Mode
• EVLA electronics designed with high headroom
requirements: up to 40 dB to 1% compression
above cold sky power.
• Whether this is sufficient depends on
time/frequency distribution of saturating RFI.
• We plan on measuring statistics for each band,
using EVLA sampler data.
• Solar mode: No change from last year. We will
test Lilie coupler-fed scheme with L-band and one
other band (TBD).
• Solar mode could be a target for descoping …
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
17
Other Characteristics
• Other characteristics (gain slope, ripple,
etc.) remain to be measured.
• Other requirements (headroom, timing, …
list others …) await testing.
• Overall – we are satisfied with performance,
but there is much yet to be done.
• We expect to meet all requirements!
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006
18