Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/alfa/galfa/docs/galspect3.ps.gz Äàòà èçìåíåíèÿ: Sat Dec 4 21:34:41 2004 Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 05:21:10 2007 Êîäèðîâêà: IBM-866 Ïîèñêîâûå ñëîâà: òóìàííîñòü ôåéåðâåðê

GALFA SPECTROMETER (GALSPECT): SETUP, OPERATION, BASICS
Carl Heiles (9/5/04), updated by Yvonne Tang (11/1/04) & Je# Mock (11/6/04)
This material is from Je# Mock, the person that designed the spectrometer. This document
is a distillation of the full scoop, which is on the webpage seti.berkeley.edu/galfa . The distillation
contains the following:
Contents
1 STARTING GALSPECT 1
2 STOPPING GALSPECT 4
3 PROBLEMS WHEN RUNNING GALSPECT 4
3.1 Rebooting GALSPECT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2 Overflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3 Missing Records in the FITS output file. . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4 What Time Is It? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 THE LO ARRANGEMENT FOR GALSPECT 6
4.1 Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2 Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5 OPTIONS FOR gdiag AND vncviewer 8
6 CHANGING THE PICTURE ON THE VNCVIEWER DISPLAY 9
1. STARTING GALSPECT
The control program for GALSPECT is called gdiag . To run GALSPECT for conventional
Galactic HI observations, perform the following steps:
1. Obtain the encryption file galfa key. If this is the first time you log into GALSPECT,
you need to copy the file galfa key from Je# Mock's directory to your home directory. To
do so, while working in your home directory, type the command

-- 2 --
cp jmock/galfa key .
2. Log into the GALSPECT computer. You should have already copied the file galfa key
to your home directory and made it readíonly by the user (chmod 0400 galfa key). Then the
appropriate command is
ssh íi galfa@galfa1
3. Check that no one else is already using GALSPECT, i.e. that no one else is running
gdiag
ps
This lists the programs running on the galfa1 computer. Look for gdiag . If it is already
running, STOP HERE!
4. Check that the data disk is mounted and has free space.
df /dump
5. Run the basic operational check of GALSPECT.
/var/diag
Let this run for 30 sec or so. If there are error messages, reboot GALSPECT (see ç3.1). If you
still get error messages, repeat until it works or until you or the equipment die of exhaustion.
6. Set the DAC levels to 10 units rms.
/var/levels
Setup the telescope and move it near the starting source before setting levels. The 1st IF and
IF routing should be configured to provide a valid signal to galspect before setting levels.
Let this run until it finishes. It prints out its current action on the screen and, at the end,
a summary. In the summary, the rms should be around 10, as you requested, and the DAC
values should be around 90. Sometimes a large RFI pulse might interfere with this operation.
If the levels do not look right, repeat this process.
Note: The gains increase with decreasing DAC number in a highly nonlinear way. From
DAC=0 to # 90 the gain decreases by # 4 db; from DAC# 90 to 255 the gain decreases by
# 36 db. Thus, low DAC values are very sensitive to signal levels. High DAC numbers should
be very rare. A low DAC number is not a problem as long as the rms is acceptable.
7. Decide how many oneísecond dumps per FITS file you want. The example below
assumes 600 (--sdiv=600), meaning that each FITS file lasts 10 minutes.
8. Decide on a project name. This should normally be the observing proposal number, e.g.
A1943.

-- 3 --
9. Create a shell script file with observation parameters. The file is usually the observing
proposal number, it should be placed in /var, make executable (chmod 775 /var/a1943) and
contains a galspect command that looks something like this:
#!/bin/sh
gdiag ígalfa ísdiv=600 íscram ílo2=256.25 íproj=A1943 ívnc
10. Start the observation.
/var/A1943
The --time option allows you to decide the number of seconds you want to run the program.
If you want to run forever, don't include the --time option.
The --scram option allows GALSPECT to listen to the network directly with the LO values.
It replaces the obsolete option --o#set.
The --lo2=256.25 option sets the frequency of the LO2 frequency synthesizer located in the
galspect rack to 2*256.25 MHz. The synthesizer is set to twice the LO2 frequency to account
for the way the analog mixers work in galspect.
The --vnc allows you to view the online graphical output on your local terminal---and anyone
else to view it on her terminal (simultaneously). And not only to view it, but also to change
the display and (yes, it's true!) the value of digitalmix. So in principle some random hacker---
or your collaborator in Timbuktu---could ruin your observation. If you replace the --vnc by
--run, then nobody can view the online output, and nobody---not even the local keyboard
on GALSPECT---can change things while you are running. If you invoke gdiag and specify
neither --vnc nor --run, then GALSPECT's local display and keyboard both function.
If you are running from o#ísite you shouldn't use the display because of network latency, so
you should not use --vnc; and if you want to make sure that local sta# don't accidentally ruin
your data, use --run.
gdiag írun íscram ílo2=256.25 ísdiv=600 íproj=A1943
11. Open another xterm and invoke the online display with
vncviewer galfa1
from LINUX machines, or
/pkg/misc/bin/vncviewer galfa1
from SOLARIS machines.
When running vncviewer, you can change the display as explained in its documentation (ç5
below). Make sure that the RA, DEC, LO1 and LO2 values on the vncviewer display match
those on the main observation panel.
It is advised that you do not run vncviewer remotely. The more people running it, the more
network bandwidth it uses which might cause the lost of data.

-- 4 --
12. Finally, the files are located in
galfaserv.naic.edu:/export/galfa.startdate.project.sequence.fits
2. STOPPING GALSPECT
To stop GALSPECT:
. If you are running vncviewer, then stop GALSPECT by typing q while the cursor is in the
plotting window.
. If you are not running vncviewer, then stop GALSPECT by typing CTRLíc.
3. PROBLEMS WHEN RUNNING GALSPECT
3.1. Rebooting GALSPECT
When there is a problem and you need to reboot GALSPECT, you can first stop GALSPECT
by typing q, then type in ps to check the pid(process id) of gdiag. After that, type in kill - 9pid
to kill the process and finally type reboot to, well, reboot GALSPECT.
When the above method does not work, you can reboot GALSPECT by powering down (turn
the key) for 1 minute. Power up and try again.
DO NOT REBOOT GALSPECT UNLESS ABSOLUTELY NECESSARY. Generí
ally speaking, it is only absolutely necessary when the /var/diag test fails.
3.2. Overflows
If the input gets too strong there are warning messages about overflows. For narrowband
spectra these messages contain the string MLFS, in which each letter represents an internal digital
operation, followed by a four digit number, one digit for each operation. All digital operations
are done in integer arithmetic, and overflow means just that. When overflow occurs, the number
saturates at the maximum value and there is no wraparound. The digits take on values from 0 to
3, with larger numbers being increasing severity.
For narrowband spectra, the operations are:
1. A means the analog to digital converter. The ADC is overflowing (saturating) when this is
set.

-- 5 --
2. M means the digital Mixer. Dan says that saturation is less serious than for the other
processes. .
3. L means the digital Low Pass Filter.
4. F means the Fourier transform computation.
5. S means the accumulator (Sum).
The meanings of the numbers are:
1. 0 means almost perfect (0í15 overflows during 1s intergration)
2. 1 means pretty good (16í255 overflows during 1s integration)
3. 2 means pretty bad (256í4095 overflows during 1s integration)
4. 3 means horrible (ƒ= 4096 overflows during 1s integration)
For wideband spectra there are only two relevant overflow parameters, F and S.
Normally, when centered on Galactic HI, GALSPECT's wide (100 MHz) band covers about
1388 to 1488 MHz. Every 12 seconds the SJU radar, centered at 1350 MHz, partially saturates
the RF electronics and causes saturation problems at the 1 level. These are not serious. It is
surprising if you don't see error messages every 12 seconds. This can change depending on time of
day, azimuth angle, and possibly other parameters.
Normally, when the EGALFA people are observing, GALSPECT's wideband is centered lower
by about 30 MHz. The SJU radar comes directly into the wide band and produces saturation
problems at the 3 level, which is very serious. But this does not indicate a problem with GALSPECT
and you should just keep observing.
GALSPECT has a few birdies. One is at the center channel, i.e. baseband DC. You'll need to
interpolate over this, or center the lines away from band center.
3.3. Missing Records in the FITS output file.
GALSPECT writes out about 2 GB per hour. If the output filesystem is being stressed by
another user, GALSPECT might complain that it has missed writing out some records. This is
serious: you are not recording data! Tell Arun; this has happened before and he has tried to arrange
that it will never happen, so he is familiar with the problem and needs to know about it. If you
want to investigate yourself, then stop GALSPECT and take a look at the activity on your output
file system.

-- 6 --
3.4. What Time Is It?
If there is a problem with time, check that the machine time on galfa is NTP locked:
ntpdc galfa1.naic.edu
> peers
remote local st poll reach delay offset disp
=======================================================================
*mosquito.naic.e 192.231.93.131 1 512 377 0.00104 0.000107 0.00780
=cuca.naic.edu 192.231.93.131 16 1024 0 0.00000 0.000000 0.00000
ntpdc>
The o#set should be within a few ms; here, it is o# 0.1 ms.
4. THE LO ARRANGEMENT FOR GALSPECT
4.1. Frequencies
GALSPECT is a baseband spectrometer that samples complex inputs, meaning that it sepaí
rates negative and positive frequencies. Thus the baseband center of each GALSPECT spectrum is
DC. The IF is mixed with the second LO, called LO2. The wideband baseband center frequency of
DC corresponds, at IF, to the frequency of LO2. The narrowband baseband center frequency of DC
corresponds, at IF, to the frequency of LO2 - digitalmix, where digitalmix is digitally generated
within GALSPECT.
Suppose you are observing the HI line at 1420.400 MHz (for this example, rounded from
1420.405752 MHz and no Doppler correction) and you want it centered in the narrowband spectrum.
To accomplish this, set the first LO to
LO1 = 1695.400 MHz = 1420.400 + 275.000 MHz
This makes the IF line frequency 275.000 MHz. The IF center of the wideband (width = 100 MHz)
GALSPECT spectrum is at the frequency of LO2, normally set to
LO2 = 256.250 MHz
and the IF center of the narrowband (width = 100
14
= 7.142857. . . MHz) is at LO2 - digitalmix.
Normally, digitalmix = -18.75 MHz, so the narrowband IF center frequency is normally

-- 7 --
Fig. 1.--- IF and RF frequencies for GALSPECT. LO1 = 1695.4 MHz, LO2 = 256.25 MHz,
digitalmix = -18.75 MHz.
LO2 - digitalmix = 256.25 - (-18.75) = 275.000 MHz
At RF, the wideband spectrum is centered at 1439.150 MHz and the narrowband one at 1420.400
MHz.
These frequencies are set as follows:
1. The LO1 frequency is set by the observing software.
2. The LO2 frequency is set by the ílo2 commandline option. The synthesizer is actually set to
twice the LO2 frequency to account for the way the mixers operate.
3. The o#set between centers of the wideband and narrowband spectra, --18.75 MHz in this
example, is the quantity digitalmix. You can set it two ways, one gdiag --mix=nn and the
other with the w option in vncviewer. There are 32 possible values, spaced by 100
32
MHz. For
nn < 16 digitalmix is negative, and for nn # 16 digitalmix is positive. The default value is
í18.75 MHz.
These relationships are illustrated in the Figure.

-- 8 --
4.2. Channels
Both GALSPECT's wideband and narrowband spectra have RF frequency increasing with
channel number. The wideband spectra has 512 channels and the center channel is number 256
(counting from zero). This wideband channel has a big DC spike.
Each narrowband spectrum has 8192 channels in the Fourier transform computation. When
writing out to a file, 513 are removed and replaced by other numbers (512 are the wideband
spectrum; the 512th is a flag). This leaves 7679 channels in the narrowband spectrum. The center
channel is number 3839 (counting from zero), and again RF frequency increases with channel
number.
5. OPTIONS FOR gdiag AND vncviewer
You can get this list by invoking gdiag with no options.
Usage: gdiag [options]
Main operating modes
íadc Print out buffer of ADC samples as text
írfft Plot real FFT of ADC channel samples
ícfft Plot complex FFT of ADC channel samples
íscope Plot oscilloscope view of ADC samples
ípatt Pattern test for data acquisition
ídump Print galfa acquisition as text
ígalfa Plot galfa data and write FITS file
írun Collect galfa data and write a FITS file
ídac Set DACs for input level of f dBM
Other options
ívnc Run as VNC server instead of console
íavg=n Average interval for histograms and FFTs
ímax Add maxíhold line FFT displays
íinput=n Take input from channel n
íppdb=f Pixels per dB for vertical scale
íadcfreq=f Use f as ADC sample frequency (MHz)
ínshift=n Set upshift of narrowband PFB before acc
íwshift=n Set upshift of wideband PFB before acc
ínpfb=x Set narrowband PFB downshift vector
íwpfb=x Set wideband PFB downshift vector

-- 9 --
íbeam=n Select beam for single beam operations
íscram Listen to the network with the LOs
ímix=0..31 Select mixer for narrowband
íta=f Signal generator A frequency
ítb=f Signal generator B frequency
ílpf=x Use LPF output instead of ADC for time domain displays
íppsint Beam 0 gets PPS from internal source
íproj=s Project portion of filename for FITS dump file
ísdiv=n Number of seconds per FITS file
ítime=n Run íírun for n seconds
ílevel=f RMS units for analog level setting
During graphical operation
Press `q' to quit program
Press `p' to create raw image file in /tmp
Press `r' to toggle maxíhold
Press `a' to toggle through galfa display modes
Press `0í6' to select beam in galfa display
Press `c/v' to modify pixels per dB on log display
Press `z/x' to change preíaccum shift in galfa display
Press `,/.' to scroll through narrow band displays
Press `' to scroll faster through narrow band displays
Press `o' to swap drawing order for polarizations
Press `m/n/b' to manually move marker
Press `w' to change mix frequency for narrowband
Press `K/L' to zoom in/out xíaxis in narrowband displays
Press `d/f' decrease/increase PFB downshift vector
Press `h' to toggle linear/log vertical display
Be careful not to hit `w' accidentally because it changes the mixer frequency
and can cause serious problems.
6. CHANGING THE PICTURE ON THE VNCVIEWER DISPLAY
It is understood that astronomers can get really bored sitting in the control room for hours.
Changing the small picture on the lower right corner of the vncviwer display can provide some
entertainment. To do so, rename a JPEG file (use one with a black background for best results) to
egg.jpg and scp it to the /var directory. 102x82 is a nice size for the mascot image.