EVLA L-Band Spectral-Line Science Below 1200 MHz

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EVLA L-Band Spectral-Line Science Below 1200 MHz

• Emmanuel Momjian
• NRAO-Socorro

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The VLA _at_ 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.

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The VLA _at_ L-band

• The VLA can also tune between 1100 and 1225 MHz,
  but with limited capability.

Perley Hayward 2008
The poor sensitivity windows are caused by
resonances within VLAs dielectric phase shifter
and/or microwave lens.
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The EVLA _at_ 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.

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Interim EVLA L-Band Sensitivity
Interim EVLA
?
EVLA
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RFI at L-band
B. Hesman
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RFI (960-1200 MHz)
B. Hesman
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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.

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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.

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PKS 1413135

• z0.2467 (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.

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PKS 1413135

• RFI

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.

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PKS 1413135

• rms 4.7 mJy/bm/ch
• Theoretical value 2.5 mJy/bm/ch

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RFI D-configuration
PKS 1413135
B-conf.
D-conf.
Baseline 16-17 60 m
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PKS 1127-145

• z0.3127 (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.

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PKS 1127-145
rms 10 mJy/bm/ch Hardly any RFI.
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RFI D-configuration
PKS 1127-145
D-conf.
B-conf.
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QSO 0248430

• z0.3941 (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.

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QSO 0248430

• rms 20 mJy/bm/ch
• RFI-clean data set.

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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
  (zHI0.53).