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EVLA L-Band Spectral-Line Science Below 1200 MHz. Emmanuel Momjian NRAO-Socorro. The VLA @ L-band. The VLA L-band system has: OMT bandwidth of 1200-1800 MHz. LNA bandwidth of 1200-1800 MHz. Post-Amp bandwidth of 1200-1800 MHz. VLA antennas can tune between 1225 and 1900 MHz. - PowerPoint PPT Presentation
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EVLA L-Band Spectral-Line Science Below 1200 MHz
Emmanuel MomjianNRAO-Socorro
The VLA @ L-band
• The VLA L-band system has:– OMT bandwidth of 1200-1800 MHz.– LNA bandwidth of 1200-1800 MHz.– Post-Amp bandwidth of 1200-1800 MHz.
• VLA antennas can tune between 1225 and 1900 MHz.
The VLA @ L-band
Perley & Hayward 2008
The poor sensitivity windows are caused by resonances within VLA’s dielectricphase shifter and/or microwave lens.
• The VLA can also tune between 1100 and 1225 MHz, but with limited capability.
The EVLA @ L-band
• EVLA antennas will tune between 930-2000 MHz.
• Currently, all EVLA antennas, except for one, use the OMTs of the VLA. However,– these EVLA antennas do not have the microwave
lens of the VLA, and
– the dielectic phase shifter is replaced with a quadrature hybrid.
Interim EVLA L-Band Sensitivity
EVLA?
Interim EVLA
RFI at L-band
B. Hesman
RFI (960-1200 MHz)
B. Hesman
RFI
• The RFI below 1150 MHz is primarily due to radar transponders used for aeronautical navigation.
• The strongest are at 1090 (air to ground) and 1030 (ground to air).
• The others are due to civilian DMEs and Military TACAN systems located every 500 kHz between 1025 and 1150 MHz.
Science Below 1200 MHz
• To test whether radio astronomical science can be delivered at the lowest frequencies of the L-band, we observed HI absorption lines at:– 1139 MHz; a frequency that the whole array
can observe.– 1082 MHz; a frequency that only EVLA
antennas can observe.– 1019 MHz; a frequency that only EVLA
antennas can observe.
• z=0.2467 (HI frequency at ~1139 MHz).
• Total time 1 hours (~75% on target) in B-configuration starting at ~7 am MST.
• Bandwidth 3.1 MHz with 127 spectral channels.
PKS 1413+135
PKS 1413+135RFI
Short baseline Intermediate baseline Long baseline
• Short baselines are clearly affected by the navigation transponders. • The pulses are 3.5 microsecond long (1.1 km) separated by 12 microsecond.
PKS 1413+135
• rms = 4.7 mJy/bm/ch• Theoretical value = 2.5 mJy/bm/ch
RFI: D-configuration
Baseline 16-17~ 60 m
PKS 1413+135
B-conf.
D-conf.
• z=0.3127 (HI frequency at ~1082 MHz).
• Total time 1 hours (~75% on target) in B-configuration starting at ~2 am MST.
• Bandwidth 3.1 MHz with 127 spectral channels.
PKS 1127-145
PKS 1127-145
rms = 10 mJy/bm/chHardly any RFI.
RFI: D-configuration
D-conf.B-conf.
PKS 1127-145
• z=0.3941 (HI frequency at ~1019 MHz).
• Total time 1.5 hours (~75% on target) in C-configuration starting at ~12 noon MST.
• Bandwidth 1.56 MHz with 255 spectral channels.
QSO 0248+430
QSO 0248+430
rms = 20 mJy/bm/chRFI-clean data set.
Summary
• Successful L-band observations were carried out with the EVLA at frequencies down to 1019 MHz.
• The RFI environment had a marginal or no effect for night-time observations and/or extended configurations.
• These results show that the EVLA, with its new L-band capabilities, will become a major player in spectral-line observations down to ~930 MHz (zHI~0.53).