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VLBI2010 and difx
Arthur Niell
MIT Haystack Observatory

2011 December 5

DiFX Workshop - Haystack

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Observing Frequency Bands
35000 30000

25000

PHASE(Arbitrary Units)

Phase
20000

Phase Delay: = / Group Delay (slope): g = /

15000

X-Band

10000

5000

0 2

S-Band: Serious RFI
4 6 8 10 12 14

2
2011 December 5

Frequency (GHz)
DiFX Workshop - Haystack

Frequency, GHz

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2


RF filter phase/noise cal Antenna Control room

Feed and LNAs cooled to ~20K Both senses of linear polarization used

Odd channels from each pol'n for one band output to each Mk5C.

2 Gigabits/sec recorded on each Mk5C. Total data rate: 8 Gbps

2011 December 5

DiFX Workshop - Haystack

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VLBI2010 Broadband System
n n

Four independent 512 MHz RF bands
Ё

Each recorded on separate Mark5C at 2 Gbps (Mk5B fmt) Each pol'n/IF becomes sixteen 32-MHz LSB channels. The channel set to be recorded is selectable. Half of the channels from each polarization are recorded. Currently: H1 V1 H3 V3 ... H15 V15 Switch soon to non-redundant spacing n e.g. 1 2 4 7 9 13 14 15

Two linear polarizations for each 512 MHz band
Ё Ё Ё Ё Ё

2011 December 5

DiFX Workshop - Haystack

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VLBI2010
n

Observations
Ё Ё Ё

One or two scans per minute scattered around the sky Scan lengths only long enough to get necessary SNR Duty cycle only about 1/3 so can use burst mode (when available) to increase instantaneous data rate.

2011 December 5

DiFX Workshop - Haystack

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S/X System
n

Mark4 (RCP)
Ё Ё

6 S-band channels 10 X-band channels: 8 upper sideband plus lower sideband on outer two. Probably 3 DBEs (2 for X and 1 for S) Single pol'n: 15 channels per DBE Dual pol'n: 8 channels per pol'n per DBE

n

DBE (when S/X stations have them)
Ё Ё Ё

2011 December 5

DiFX Workshop - Haystack

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Correlation ­ DBE to DBE
n

Correlate all cross-hands

2011 December 5

DiFX Workshop - Haystack

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Correlation ­ Mk4 to DBE
n

Broadband to Mark4 cross-correlation
Ё Ё Ё Ё

8 MHz Mark4 channels 14 USB + 2 LSB 32 MHz PFB channels LSB May have multiple 8 MHz channels within 32 MHz channel Each type to be correlated against both types in same scan Mark4 channels RCP Broadband channels linear polarization

n

Polarization
Ё Ё

2011 December 5

DiFX Workshop - Haystack

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Mark4 vs DBE
8-MHz

analog channels (Mark5A or Mark5B ­ one module)

S1U S2U S3U S4U S5U S6U X1L X1U X2U X3U X4U X5U X6U X7U X8L X8U

PFB 32 MHz channels (Mark5C - 3 modules Mk5B format)
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---| S-band (2 pol'n) |---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---| Xlow-band (512 MHz) (2 pol'n) Xhigh-band (512 MHz) (2 pol'n) |---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Correlate Mark4 against both linear polarizations of the broadband system

2011 December 5

DiFX Workshop - Haystack

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Example of 8 MHz vs 32 MHz
X1L X1U
-------- --------

X2U
--------

Mark4 (8 MHz)
RCP

PFB (32 MHz LSB)
-------- -------- -------- --------------- -------- -------- -------Vertical pol'n Horizontal pol'n

0 frequency(MHz) 32

2011 December 5

DiFX Workshop - Haystack

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Correlation
Mark4 Mark4

PFB

PFB

2011 December 5

DiFX Workshop - Haystack

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Simplification
Put DBEs everywhere using PFB. Put all data on one module using Mark6!

2011 December 5

DiFX Workshop - Haystack

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Post-correlation
Coherently fit all four bands and all four cross-hands for phase delay, amplitude, rate and differential ionosphere. Incorporate source structure phase. May have to be incorporated in the coherent fit.

2011 December 5

DiFX Workshop - Haystack

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2011 December 5

DiFX Workshop - Haystack

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2011 December 5

DiFX Workshop - Haystack

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Quadridge Feed Horn (QRFH)
n

California Institute of Technology Design
Ё Ё Ё

Sandy Weinreb Ahmed Akgiray Bill Imbriale

n

2-
14 GHz Unbalanced Design
Ё

One single-
ended port per polarization

n

Designed for Patriot 12m Antenna Shaped Optics
Ё

Adaptable to other antenna optics

n

Overcomes limitations of commercial quadridge designs Have observed 60% efRiciency on 12m antenna

n

2011 December 5

DiFX Workshop - Haystack

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12m antenna at Goddard Geophysical and Astronomical Observatory, Greenbelt, Maryland

2011 December 5

DiFX Workshop - Haystack

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http://ivscc.gsfc.nasa.gov/about/wg/wg3/ IVS_WG3_report_050916.pdf
18 2011 December 5

ftp://ivscc.gsfc.nasa.gov/pub/ misc/V2C/ TM-2009-214180.pdf

DiFX Workshop - Haystack


12m performance
Current

fiber link noise

2011 December 5

DiFX Workshop - Haystack

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VLBI2010 signal chain
n n n

Cooled broadband feed and LNAs UpDown Converters (4)
Ё Ё Ё Ё Ё

Usable as-is for 2-13 GHz Hardware complete Firmware complete, under test Interface/command software complete; under test In use/testing by VLBA Functionality complete; minor bugs In use/testing by VLBA
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RDBE digital back end (4)

n

Mark5C recorder (4)
Ё Ё

2011 December 5


Thank you.

2011 December 5

DiFX Workshop - Haystack

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2011 December 5

DiFX Workshop - Haystack

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