New frequencies
EVLA receivers often are sensitive over a wider frequency range
than their VLA predecessors, and observations at these until now
unattainable frequencies have become possible. See here for the most recent receiver upgrade
schedule. Note that:
- at these new frequencies, only data from EVLA antennas can be
used; VLA antennas do not produce useful data
- JObserve and observe does not support the creation of the required
observe files. Before our new Observation Preparation Tool (OPT) is
operational, refer to the Observation Preparation section below
- observations in IFs A/C below the traditional lower VLA frequency
limit suffer from saturation issues caused by too large a frequency
shift in the signal path. IFs B/D will give useful data since their
lack of automatic attenuation prevents the saturation seen in IFs A/C.
We see this behavior in L-band below 1250 MHz and in C-band below 4400
MHz
- The maximum IF difference for EVLA antennas is currently 10 GHz,
subject to the restrictions of the receiver bandwidth. If you want to
tune the IF pairs further apart than the maximum JObserve allows (500
MHz), please contact Gustaaf van
Moorsel
Band-specific information
Observe file preparation specifics
- Since only EVLA antennas can observe at the new frequencies, there
is no danger of small frequency changes introducing phase jumps on VLA
- EVLA baselines, and Doppler tracking can be used (see here for further details)
- If you don't want Doppler tracking, you will need to specify the
appropriate VLA LO settings directly in the observe file. Note that
JObserve will complain - the LO settings in the observe file are only
used to set the appropriate values in the EVLA LO chain. In the
specific case of L-band observing between 1000 and 1200 MHz we have
made an online
version of the LOSER program available
- For general help on finding LO values in order to arrive at the sky
frequency of your choice, please contact Gustaaf van Moorsel
|
National Radio
