Broadband

F

ast

F

ourier

T

ransform

S

pectrometer (

FFTS

)

Bernd Klein

Max-Planck Institut für Radioastronomie, Bonn - Germany -

B.Klein Berkeley 2008

FFTS ::

A short “history” ...

2.5 GHz >8k channels 2.5

2.0

1.5

1.0

0.5

0.1

1 GHz 8k channels 2 x 50 MHz 1k channels 1.5 GHz 8k channels 100 MHz ? channels 1.8 GHz 8k channels 2003 2004 2005 2006 2007 2008 2009 year B.Klein Berkeley 2008

FFTS :: The MPIfR-Board

IF input (0 - 3 GHz) Analog Power Supply GPS/IRIG-B Time decoder ADC FPGA

Signal pro cessing

ADC Synthesizer (AD9517-n) Power Supply (1.2, 1.9, 2.5, 3.3 V) 100 MBit/s Ethernet 

Instantaneous bandwidth: 0.1 – 1.8 GHz



Spectral resolution @ 1.5 GHz: 212 kHz



Stability (spec. Allan Variance): > 1000 sec.



Calibration- and aging free digital processing

5 Volt Data B.Klein Berkeley 2008

FFTS :: Stability

ADC Transistor as „Heater“ The spectroscopic variance between two 1 MHz broad channels, separated by 800 MHz within the band, was determined to be stable on a timescale of ~4000 s.

B.Klein Berkeley 2008

APEX :: Atacama Pathfinder EXperiment Telescope: Location: Coordinates: Diameter: f/D: Beam width: Main reflector: Surface accuracy

:

Pointing accuracy: Mounting: Receiver cabins: Mass: Manufacturer:

Llano de Chajnantor, 50 km east San Pedro de Atacama, northern Chile Latitude : 23º00"20.8' South Longitude :67º45'33.0" West Elevation : 5105 m 12 m 8 (FWHM) 7.8" * (800 / f [GHz]) 264 aluminum panels, average panel surface rms 5 micron 17 micron rms 2" rms over sky Alt-Az 2 Nasmyth + 1 Cassegrain 125 000 kg Vertex Antennentechnik B.Klein Berkeley 2008

CHAMP + :: Array-RX 660/850 GHz window

B.Klein Berkeley 2008

AFFTS :: Array-FFTS for APEX Bandwidth: 32 x 1.5 GHz = 48 GHz (option 58 GHz) Spec. channels: 32 x 8k = 256k channels @ 212 kHz

B.Klein Berkeley 2008

AFFTS :: FFTS-Master

B.Klein Berkeley 2008

AFFTS :: Software / Monitoring

test line @ 300 MHz

FFTS Control Software:

• multi-threaded software / Linux • one thread per FFTS-board (smoothing, leveling, RFI-filter, ..) • communication telescope / FFTS: SCPI protocol (UDP/ASCII), e.g.

APEX:AFFTS:band1:cmdBandwidth 1500 • data flow: TCP (header + spectra) • FFTS Monitor Tool (LabView) B.Klein Berkeley 2008

The Lab-FFTS

B.Klein Berkeley 2008

FFTS :: Signal Processing

Unlike the conventional windowed-FFT processing, a more efficient polyphase pre-processing algorithm has been de veloped with significantly reduced frequency scallop, less noise bandwidth expansion, and faster sidelobe fall-off.

Frequency response of the optimized FFT signal processing pipeline

Equivalent noise bandwidth = 1.16 x frequency spacing

B.Klein Berkeley 2008

FFTS :: FPGA configurations

Today, implemented FFTS board / FPGA configurations are: • 1 x 1.5 GHz bandwidth, 1 x 8192 spectral channels, ENBW: 212 kHz (default core) • 1 x 1.8 GHz bandwidth, 1 x 8192 spectral channels, ENBW: 255 kHz 1.9 GHz is possible by using selected FPGAs with highest speed grades!

• 1 x 750 MHz bandwidth, 1 x 16382 spectral channels, ENBW: 53 kHz • 1 x 500 MHz bandwidth, 1 x 16384 spectral channels, ENBW: 35 kHz • 1 x 100 MHz bandwidth, 1 x 16384 spectral channels, ENBW: 7 kHz (in lab test) • 2 x 500 MHz bandwidth, 2 x 8192 spectral channels, ENBW: 71 kHz (in lab test)

The Equivalent Noise Bandwidth (ENBW) is the width of a fictitious rectangular filter such that the power in that rectangular band is equal to the (integrated) response of the actual filter.

B.Klein Berkeley 2008

FFTS :: in world-wide use

The superior performance, high sensitivity and reliability of MPIfR FFT spectrometers has now been demonstrated at many telescopes world-wide.

W3(OH) SgrA circum-nuclear disk CO(2 –1) Spectrum towards Orion-KL. The high-excitation CO(7-6) transition at 806 GHz was observed with the central pixel of the CHAMP+ array.

Further details : • B. Klein, et al., Proceedings of the 19th ISSTT, Groningen 28-30 April 2008 • http:://www.mpifr-bonn.mpg.de/staff/bklein B.Klein Berkeley 2008

The Effelsberg FFTS (EFFTS) Applications:

• • Spectroscopy Pulsar Search :: 16 x 100 - 500 MHz bandwidth, 8192 and 16384 channels :: 16 x 250 MHz bandwidth, 512 channels, 32/64µs dumping

Installation & Commissioning: August this year!

B.Klein Berkeley 2008

The Effelsberg FFTS :: hardware Board modifications:

• • Dual input ADC :: National ADC08D1500, 2 x 750 MHz bandwidth GigaBit Ethernet :: Marvell 88E1111, UDP: 85 MBytes/sec cont.

I-Input Q-Input Marvell GigaBit chip TCP 100 Mbits/s UDP 1 Gbits/s B.Klein Berkeley 2008

EFFTS :: pulsar signal processing Performance:

• • FPGA processing Dump time [µs] • Data rate @ 32µs :: 250 MHz bandwidth & 8-tab polyphase filterbank with 512 channels, ENBW: 515 kHz :: 32, 64 or 128, 16 x 512 channels (32-bit float) 1k Bytes tail (dump counter, GPS/IRIG-B time,...) :: ~64 MBytes/sec B.Klein Berkeley 2008

FFTS :: The 2.5 GHz development

Currently in development:

The 2.5 GHz bandwidth FFTS for GREAT

Goal: 2.5 GHz instantaneous bandwidth with adequate spectral resolution (~100 kHz), to be operational in time for SOFIA‘s early science flights in summer 2009!

B.Klein Berkeley 2008

FFTS :: The 2.5 GHz development First (lab) results: 2.5 GHz with 512 channels

Next step: Increase the number of spectral channels by replacing the Virtex-4 SX55 by the new Virtex-5 SX240T or 3/4 x Virtex-4 SX55.

B.Klein Berkeley 2008

MPIfR FFTS :: Summary

Advantages of our new generation of compact FFT spectrometers:  FFTS provide high instantaneous bandwidth (1.5/1.8 GHz demonstrated in field tests, 2.5 GHz achieved in lab tests) with many thousands frequency channels, thus offering wideband observations with high spectral resolution without the complexity of the IF processing in a hybrid configuration.

 They provide very high stability by exclusive digital signal processing. Allan stability times of > 1000 seconds have been demonstrated routinely.

 Field-operations of our FFTS over the last 3 years have proven to be very reliable, with calibration- and aging-free digital processing boards, which are swiftly re-configurable by Ethernet for special observation modes.

 Low space and power requirements – thus safe to use at high altitude (e.g. APEX at 5100-m) as well as (potentially) on spacecrafts and satellites.

 Production cost are low compared to traditional spectrometers through use of only commercial components.

B.Klein Berkeley 2008

FFTS :: Contact, Distribution Contact:

For further information about the MPIfR FFT spectrometer technology, future developments and applications, please contact Bernd Klein ( [email protected]

) at the Max-Planck Institut für Radioastronomie in Bonn, Germany.

http://www.fft-spectrometer.info

Distribution of standard FFT spectrometer (1.5 GHz / 8192 channels) by:

http://www.radiometer-physics.de

B.Klein Berkeley 2008