GBT Spectrometer Spigot Card for Pulsar Observations
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Description:
- The GBT Spectrometer Spigot Card (or Spigot system) is a
new pulsar-search backend for the 100-m Green Bank
Telescope.
- It uses the extremely powerful and flexible Digital
Spectrometer to perform auto-correlations of the data very
rapidly, then dumps the data to a PC with a 2-TB RAID.
- The hardware for the Spigot system is:
- The spectrometer
- Two custom digital logic cards designed by NRAO
engineer Ray Escoffier. These cards accumulate and sort the
data, then pack/decimate it for output.
- A PCD-60
data-acquisition card sitting in the PC
- A PC (dual Pentium 2.0-GHz)
- A 2-TB RAID (using 16 160-GB IDE disks)
- The data format is FITS
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Status:
- We achieved first light pulses in November 2002
- Currently, we are developing the observing software
- Full integration into the GBT observing plan is anticipated
in spring 2004
- Before that, observing may be possible in "Expert" mode
(in collaboration with project members)
- Testing results:
- 2003-Aug:
- We successfully observed a number of pulsars (isolated,
binary, millisecond)
- We observed at 1.4 GHz, 2.0 GHz, and 9.0 GHz
- We observed a pulsar (B1929+10) simultaneously with the BCPM and measured the same period/TOAs with both
- We have done timing analyses of 3 binary msps, and the
TOAs do not show any systematic trends
- A report (ps, pdf) detailed the testing
- Plots for:
More plots and explanations are in the report.
- 2003-Sep-15:
- Modes 1-6 have all been checked out with an artificial
noise source
- Modes 41-46 have all been checked out with an artificial
noise source
Software status:
- Scott Ransom's PRESTO analysis package works with Spigot data
- Quick-look python scripts are now available
2003-Sep-22:
- Double-Nyquist sampling has been tested for modes 1-6.
This gives (for these modes) 1024 channels across 400 MHz,
instead of 800 MHz. See bandpass: the same instrumental
bandpass is shown in both panels, but the bottom panel has
0.78 MHz/channel, while the top has 0.39 MHz/channel.
2003-Dec:
- Got modes 15,16,55,56 to work. These are the first modes
with Nlags != 1024
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Specifications:
- The data-rate is held constant at 25 MB/s.
- Within that limit, the system is extremely flexible.
- The system can use either 1.6-GHz samplers (800 MHz bandwidth,
for high frequencies) or 100-MHz samplers (50 MHz bandwidth, for
low frequencies)
- The number of lags, the sampling time, the precision, and the
number of independent samplers can all be varied as long as the
data-rate is constant
- Number of Lags: 256-2048
- Sampling Time (microsec): 2.56-81.92
- Bits/sample: 2-16 (16- and 8-bits are only available in certain
configurations)
- Polarizations: 1, 2, 4 (full Stokes), or 2 summed
- RF bands: 1 or 2
Examples
of Spigot Modes (many more combinations are possible)
|
Lags
|
Sample
Time (microsec)
|
Bits/sample
|
Polarizations/RF
bands
|
1024
|
81.92
|
16
|
1
or 2 summed
|
1024
|
40.96
|
8
|
1
or 2 summed
|
1024
|
20.48
|
4
|
1
or 2 summed |
1024
|
81.92
|
4
|
4
(full stokes)
|
1024
|
10.24
|
2
|
1
|
2048
|
40.96
|
4
|
1
or 2 summed
|
512
|
10.24
|
4
|
1
or 2 summed
|
Top | Description | Status | Specs | Collaboration | Links/Docs
Collaboration:
Top | Description | Status | Specs | Collaboration | Links/Docs
Links/Documentation:
Top | Description | Status | Specs | Collaboration | Links/Docs
<--BACK to where it all started
If you have any additional questions or comments, please contact:
David Kaplan
email: dlk@astro.caltech.edu
phone: 626-395-4051
fax: 626-568-9352
Department of Astronomy
California Institute of Technology
MS 105-24
1201 E. California Blvd.
Pasadena, CA 91125
Last modified: Fri Dec 3 06:57:20 PST 2004
