updated
September-06-00 / jn
As
described
here the 8192-channel-correlator can be used for normal continuum
observations.
That especially is interesting for line observers in order to get
calibration
information of continuum or line sources.
Lately the 8192-Correlator got a
special external
filter unit making it possible to have bandwidthes below
the
minimum of 10 MHz as originally possible (See
here !).
Using the correlator
for line pointing one can observe line sources for pointing like
an ideal double-horn configuration eliminating
atmospheric
effects. An incomming signal from the receiver can be splitted
into
two correlator IF-channels. One correlator channel is well adjusted to
the frequency of the line with a selectable bandwidth of 20, 10, 5, 2.5
or 1.25 MHz, another one is shifted for example for 20 MHz respect to
the
line. Because of the architecture of the correlator only if-channels 1
3 5 and 7 have the narrowband external filters beneath 10 MHz. To serve
also receivers with 2 polarisations the output channels of the
correlator
(i.e. the channels for the continuum output) are arranged in the
following
way:
Channel 1 of the correlator contains
the line
of Receiver A.
Channel 3 of the correlator contains
the line
of Receiver B.
Channel 5 contains a shifted signal
(20 MHz) of Receiver B.
Channel 7 contains a shifted signal
(20 MHz) of Receiver A.
For reduction
using
continuum
beam switch mode (i.e. the differences 1-7 and 3-5) not only provides
a good signal to noise ratio of the line signal, but more over the
atmospheric
effects should be eliminated.
OBSe
I added another parameter for
<cmode> in
POINTING and
the other continuum procedures. That automatically uses the 8192-AC in
the mode described above, i.e. observing a strong line. One only must
specify
for <cmode> the parameter D(o_line) instead
for example T(otal) or L(oad) ...
The
parameters to
specify
are:
FRQRX
< linefrequency [GHz]>
For receivers,
where it
is possible, otherwise use
SET FREQUENCY_C <
linefrequency
[GHz]> <lsb or usb>
SET NBAND
< bw bw bw bw bw bw bw bw>
The
bandwidthes for
the 8 channels of the correlator in the range for bw = 20 - 1.25 MHz.
POINTING D(o_line)
Automatically
switches
to the 8192-AC and selects all parameters for the continuum-line-mode
and
does the Pointing.
The
Online-Display
automatically displays the calibrated signal of Receiver A or B.
Set PEN 1
will display
Receiver A (channel 1)
Set PEN 2
will display
Receiver B (channel 3)
For manually doing a line pointing in OBSE
the
following
commands are neccesary
(if not using POINTING D):
set backend_c f
! Choose continuumbackend as filterunit
(8192 AC)
set pen 1 7
! beamswitch 1-7
or
set pen 3 5
! beamswitch 3-5
set nsplit 4 offr
! use splitmode 4 with absolute offsets
set nband 2.5 2.5 2.5
...
! bandwidth for example 2.5 MHz (must be given exactly !)
set nfrq 0 0 0
0 20
0 20
0 ! offset in channel 5 and 7 is 20 MHz
set nchann 2
*
! contribute two IFs to all correlator channels
set frequency_c <line_frq>
! set continuum frequency to line frequency in GHz
pointing beam
! pointing now with beamswitch for display
or
pointing total
! or using only one channel for display ( 1 or 3 )
