Currently known constraints for LWA1 observing as of September 17, 2018
- Number of beams: Since August 2018, only three beams are
operational on LWA1. It is not clear at this time when/if the fourth
beam will come back online. (9/17/2018)
- Injected noise: Between 9/18/2013 and 10/3/2013 the LEDA
FEEs were switched on and being included in beams. This resulted
in the LEDA noise switching cycle injecting noise for 1 sec out of
every 3 seconds. In the future we will not be including the
LEDA outriggers in the beams.
- DRX Dropouts: Every so often there appears to be a small
drop in power associated with BAM commands that lasts for about 1
second. Cause of this is not yet known. Not all DRX observations are
- Zeros in Spectrometer Mode: A very small fraction of
spectrometer data <0.001 percent has shown zeros in a few
specific channels in some spectrometer modes.
- DRX Timing: It appears that data from DRX
observations are fast by 1 second. Cause of this is not
yet known. (7/2/2013)
- TBN Timing: It appears that data from TBN
observations are 10.24 msec delayed. This is likely
due to sampling 1024 samples at 100 kSPS.
- TBN bandwidths: Only the widest TBN bandwidth
(100 kSPS) is known to be working. If you need a reduced
bandwidth mode, please send an e-mail request to the Director.
- Pointing: Currently thought to be good to about
0.1 degrees rms at elevations above 40 degrees. To read
the full history of pointing corrections (and errors)
look at LWA
memo 194 by Dowell \& Grimes. (5/1/2013)
- Running beams simultaneously with TBN or PASI: At the moment this is not recommended due to apparent bad interactions between these modes (internal to the digital processing subsystem). (3/19/2012)
- Limits on available observing modes: None. All
observing modes, including custom beamforming, are
- Creation of Session Definition Files (SDFs):
- Within the SDF, each 'observation' has to be 1,024
steps or less. If your file contains more steps, please submit your
schedule as a series of shorter observations. (2/1/12)
- Each SDF can contain maximum 149 'observations'. If your file contains more observations, please submit your
schedule as a set of shorter SDFs. (6/14/12)
- Each beam and TBW/TBN set need a separate SDF to be prepared. The SessionGUI schedules beams separately. If you have more than one beam that may differ only in e.g., the tunings, schedule one beam first. Then copy the
text file for the other beams, and edit the tuning frequency. (2/26/12)
SDFs for TBW/TBN captures under SDF control are now working (8/14/2012)
- No time gaps allowed within an SDF: If your planned observation has several
parts that are not to be observed continously, please prepare
separate SDFs for these observations.
- SDF length limit: SDFs of 6 hours or less are currently easier to schedule for the operator, if your observations are much longer please submit several shorter SDFs.
- For limitations of spectrometer observing modes look at
this interactive table,