1. EVLA Advisory Committee Meeting
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

2. EVLA Advisory Committee Meeting
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

3. EVLA Advisory Committee Meeting
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

4. EVLA Advisory Committee Meeting
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

5. EVLA Advisory Committee Meeting
Antenna-Efficiency
Band
Req.
Obs. L
.45 S
.62
TBD C
.60 X
.56 U
.54 K
.51 A
.39 Q
.34 *
Table shows requirements and status.
Observations made on known standards calibrated with hot/cold loads.
We are on track to meet all requirements.
* Observations made without optimal focus or subreflector position. Further holography required.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006

6. EVLA Advisory Committee Meeting
Antenna Polarization
Linear: Requirements set to give < 5% cross-polarization 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

7. 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

8. EVLA Advisory Committee Meeting
More Polarization
Antennas 13 x 16
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006

9. EVLA Advisory Committee Meeting
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.
Band
Req.
Obs. L 27 28 S
TBD C 24 X 31 U 38 K 61 45 A 55 Q 70 65
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006

10. 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

11. 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

12. EVLA Advisory Committee Meeting
Bandpass Stability
A very difficult spec has been set: 0.01% amplitude, and 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

13. VLA Amplitude Differential Hourly Snapshots
VLA antenna 17 amplitude.
Ripple due to waveguide reflections.
Magnitude ~ 0.5%
Typical for all VLA antennas.
RCP LCP
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006

14. EVLA Advisory Committee Meeting
VLA Phase
Showing VLA ripple in phase.
Magnitude ~ 0.5 degrees.
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006

15. 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

16. EVLA Advisory Committee Meeting
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 LCP
Rick Perley
EVLA Advisory Committee Meeting
May 8-9, 2006

17. EVLA Advisory Committee Meeting
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

18. 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