SMA Man Page: spect
SubMillimeter Array Project
SMA Man Page: spect
Author: Charles Katz
Last Update: 12/18/98
spect(1) User Commands spect(1)
spect - autocorrelation spectrometer control program
-h prints a help message
-v prints version information
-a antenna_number specifies the antenna number on which
to do chopping/position-switching/
phase-switching; may be 2 or 3;
default is 2; this number may be
changed while spect is running
-d filename turns on diagnostic/debugging output
and writes it to filename; typically
this will be a /dev/ttyXX file; this
option causes a lot of output to be
generated
-g Gunn_mult specifies the Gunn oscillator
multiplication factor for the chosen
observing frequency; acceptable range
is 1-8; default is 2, corresponding
to 230 GHz
-s (silent mode) disables beeping at the
end of each accumulation
Spect is a control program for use with the Spaceborne Inc.
Autocorrelation Spectrometer and the Submillimeter Array
hardware. It runs under LynxOS 2.3.0 or 2.4.0.
The top part of the spect display lists operating informa-
tion:
Day of year : UTC, read from the system clock
Time of day : UTC, read from the system clock
GM : Gunn multiplier setting (see -g flag)
Ant : Antenna number (see -a flag)
Temp : Correlator chip temperature (Celcius)
Bandwidth : correlator bandwidth in MHZ (must
agree with the frequency at the
clock input to the spectrometer)
Integration Time : in seconds
Type : "Spec" or "Corr", indicating
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spect(1) User Commands spect(1)
calculation of spectrum or
autocorrelation of input signal
Mode : Auto Trigger, Manual Trigger,
SMA Chopper, SMA Position Switching,
or SMA Phase Switching
Thresholds : Digitizer threshold settings
State Fractions : Fraction of samples falling into
each of the four quantization levels
(see below)
Output File : Output file name and number of
integrations written
Baseline Subtr. : (auto and manual trigger modes only)
indicates whether baseline
subtraction is enabled and when the
baseline scan was acquired
System Temp : (SMA Chopper and Position Switching
modes only) Calculated wideband
system temperature in Kelvin
Source : Name of source under observation;
read from value placed in reflective
memory by the track program
Ave. Length : Indicated number of integrations
accumulated to form a spectrum; thus
total integration time is
(Integration Time)*(Ave. Length);
spect will beep when the full
averaging length has been performed
(unless silent mode was selected
with the -s switch)
Delay Line : Setting of spectrometer's internal
delay line
The middle part of the display provides status information
and user interaction.
The bottom part of the display lists the available keyboard
commands.
Auto Trigger mode: Each time an integration ends, a new
one is started immediately. The
results are written to the data file
(if open) when (Ave. Length)
integrations have been performed.
Manual Trigger mode: When an integration ends, the program
pauses. A new integration must be
started manually, with the (s)
keystroke. The results are written
to the data file (if open) when
(Ave. Length) integrations have been
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spect(1) User Commands spect(1)
performed.
SMA Pos. Sw. mode: Integrations are started by receipt of
a VXI interrupt (via reflective
memory) from the "track" program
running on the antenna specified with
the -a switch. Interrupts are sent
by "track" when position changes are
complete. The integration time must
be less than antenna dwell time (see
NOTES below). The spectrum is
calculated only when consecutive
on/off or off/on scans are collected
without interruption. Data are
written to the file (if open) after
(Ave. Length) integrations have been
performed.
SMA Chopper mode: Same as Phase Switching, except
interrupts are sent by track after
moving the chopper.
SMA Phase Sw. mode: Switches the phase at the LO through
requests to the DDS. Sequence is as
follows:
Request 0 degree phase offset
Perform 1 integration
Request 180 degree phase offset
Perform 1 integration
Calculate real data (difference
between 0 and 180 degree
integrations)
Request 90 degree phase offset
Perform 1 integration
Request 270 degree phase offset
Perform 1 integration
Calculate imaginary data (difference
between 90 and 270 degree
integrations)
Average real and imaginary data
separately with previous real
and imaginary data
If (Ave. Length) real and
(Ave. Length) imaginary data
have been averaged, calculate
phase and magnitude from real
and imaginary data; write
results to file (if open)
Before acquiring data, the spectrometer digitizer thresholds
must be calibrated. Make sure the input power is typical of
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spect(1) User Commands spect(1)
what will be seen during observation, then issue the "Cali-
brate Digitizer Thresholds" command (keystroke d). The
digitizer thresholds will be adjusted so that the state
fractions line reads
-3(0.184) -1(0.316) +1(0.316) +3(0.184)
If the state fractions drift from these values over time,
the power level at the input to the correlator has changed
and the thresholds should be recalibrated.
For power levels appropriate for the spectrometer, the digi-
tizer thresholds will be in the following ranges:
low -14000 to -8000
zero -1000 to +1000
high +8000 to +14000
Data files may be in ASCII format or FITS format appropriate
for importation into CLASS.
ASCII (Auto/Manual Trigger Modes) -- each row contains
status information, timestamps, and 128 total
power data points (or total power difference if
baseline subtraction is on)
ASCII (Chopper/Position-Switch modes) -- If there is no
Tsys calibration, the 128 data points are
(on-off)/off combinations; if Tsys has been
calibrated, the data points are Tsys*(on-off)/off
combinations; the on and off data will also be
saved in the same file.
ASCII (Phase Switch mode) -- Two files are opened; if
the base filename is entered as source1.asc, then
the files opened are source1.asc.mag and
source1.asc.phs, containing magnitudes and phases
of the data
FITS (all except Phase switch mode) -- A base filename
is requested along with several observing
parameters:
Line Frequency in GHz
Receiver IF center frequency in GHz =
(Line Frequency - local oscillator
frequency)
Correlator IF center frequency in MHz =
final downconverted frequency of line
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spect(1) User Commands spect(1)
Then, each integration is written into a new FITS file
(required for reading into CLASS). If the base filename
is source1.fits, then the spectra will be saved in
source1.fits.1, source1.fits.2, source1.fits.3, etc.
Position Switching mode: start spect with the -a switch to
select the antenna to switch. Typically the track
program is set to a switch period of 40 seconds
(i.e. 20 seconds on-source and 20 seconds
off-source). The integration time would be set to 19
seconds, and the averaging length to 1.
Chopper mode: start spect with the -a switch to select the
antenna to chop. Typically the track program is set
to a chopper period of 2 seconds (i.e. 1 second
on-source and 1 second off-source). The integration
time would be set to 0.8 seconds, and the averaging
length to something longer. For example, an
averaging length of 30 would yield 30*0.8 = 24
seconds total integration (with 50% efficiency, of
course)
Phase Switch mode: start spect with the -a switch to
select the antenna on which to perform the phase
switching (typically antenna 3). The fastest
allowable integration time for phase switching is
0.25 sec. 0.5 seconds is a safe choice. An
averaging length of 30 yields a full complex
measurement approximately once per minute (30 *
0.5sec * 2phases), with 30 seconds effective
integration time in each of the phase and magnitude
measurements.
Only a discrete number of integration times are available,
depending on the clock frequency; when an integration time
is set, spect will find the closest allowed value to that
requested.
There is about 200ms of overhead associated with each
integration when instrument type = Spec. Thus the integra-
tion time must be at least this much shorter than any exter-
nally imposed switch period. For example, if the chopper
spends 1 second on source, then the integration time must be
less than 0.8 sec.
Since spect uses the VXI bus during chopping and position-
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spect(1) User Commands spect(1)
switching, the environment variable NIVXIPATH must be set
properly.
These two files must be present in the directory with spect:
x4c128in.rbt contains configuration data for the
correlator; read by spect on startup
spect.prm contains parameter settings for spect;
used to maintain state between program
exectutions
The device driver for the spectrometer must running:
/dev/idsd spectrometer device special file;
device driver idsd
If spect must be killed externally, send SIGTERM or SIGINT.
SIGKILL will cause the program to hang and be unkillable.
The machine will have to be rebooted.
Charlie Katz
ckatz@cfa.harvard.edu
617 496 7935
spectmon, track
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