WAPP Dual Board Mode
The WAPP dual board mode for single pixel receivers
The capability to use the WAPPs in dual board mode for single pixel
receivers was added in CIMA version 2.3 with first observations
performed on 1 April 2007. This is the mode when the two boards of
each WAPP are used as independent spectrometers allowing each WAPP to
cover up to 200 MHz bandwidth. With this mode it is thus possible to
double the bandwidth covered with the WAPP during single-pixel
receiver observations from 400 MHz to 800 MHz, and the mode has thus
often been referred to as the 800 MHz mode. This is certainly
what it is mostly going to be used for but there is nothing preventing
an observer for using the dual board mode with narrower bandwidths all
the way down to 0.1953125 MHz.
The following freedoms and restrictions apply in the current
implementation of the dual board mode:
- Any WAPP or any combination of WAPPs can be used. You don't need
to run all WAPPs and You don't need to select WAPPs in sequential
order. If You, for some reason, want to use only WAPP-2 and WAPP-4,
You can do that.
- It is either dual board mode or single board mode for all selected
WAPPs. If You select to use dual board mode, all enabled WAPPs will be
running in dual board mode. You can not mix and have one WAPP running
in dual board mode and another one running in single board mode.
- You can only have one bandwidth selection per WAPP. When using
dual board mode, both boards on the same WAPP will use the same
bandwidth. You will thus only see one bandwidth menu for each WAPP in
the user interface when You are running dual board mode. You can,
however, select different bandwidths for different WAPPs. If You want
to cover 600 MHz of band and at the same time get some high resolution
spectra of two known lines in Your band, You could set up three of the
WAPPs to use 100 MHz and set the fourth one to use a narrow bandwidth.
- You can use any bandwidth selection normally available for the
WAPPs from 0.1953125 to 100 MHz.
- You can use any WAPP configuration normally available for the
WAPPs. As with the bandwidths, the same configuration will be applied
to both the boards on each WAPP, but You can have different
configurations on different WAPPs. NOTE though that '2 chan, 9-level'
and '9-level, polarization' can NOT be used together with 100
The example above shows how to set up an observation for dual board
mode with the new 'Receiver IF/LO selection menu' introduced in CIMA
version 2.3. In this example, the C-band receiver has been chosen and
the WAPP mode has been selected to be 'Dual board' to allow us to
cover 800 MHz between 5000 and 5800 MHz with the center frequency set
to 5400 MHz. The rest frequencies for the eight boards have then been
put in with a separation of 100 MHz. The first line of rest
frequencies refers to the first board of each WAPP while the second
line refers to the second board. Note the order of the frequencies; an
observer is, of course, free to put the selected bands in any order,
but this is the order that will make the consecutive bands to be
numbered sequentially in the CIMAFITS file.
In the example given, we have set the boards with 100 MHz
separation. This may not be the optimal set-up for projects like
searches for molecular lines, since the bandpass falls off at the
edges of each band. For such projects it may be better to have a bit
of overlap (10-15 MHz) at the edges to ensure that any interesting
line doesn't fall in the gap with reduced sensitivity between the
The data is currently written to FITS-files in a similar way as ALFA
data is written. The INPUT_ID keyword is given a value between 0 and 7
to indicate which board the data refers to, with 0 and 1 being board A
and B on WAPP-1. The two arrays SYNFRQ and MIXER are 4-value arrays
and are set up to contain the synthesizer frequencies and mixer
settings for the four A-boards in records with INPUT_ID = 0, 2, 4 and
6 and for the four B-boards in records with INPUT_ID = 1, 3, 5 and 7.
Other variables have currently not been modified.
For pulsar data, the files look very much like ALFA data. However,
there is a change of the pulsar file headers to include information on
the eight channels as well as a new flag. The 'wapp_split' program can
extract the data from the two boards into separate files and this
program is replacing the old 'alfasplit' program.
You can return to the main CIMA page by clicking here.
This page is administered by Prakash Atreya
( patreya (a) naic . edu ) and was last updated on 19 September 2008.