Atacama Large Millimeter/submillimeter Array Expanded Very Large Array Robert C. Byrd Green Bank Telescope Very Long Baseline Array DBE Implementation for VLBA Keith Morris & Matt Luce CASPER2010 August 18 th, 2010

DBE Contributors Haystack: – Alan Hinton, Arthur Niell, Shep Doeleman, Mikael Taveniku, Christopher Beaudoin, Chester Ruszczyk, Russ McWhirter NRAO: – Doug Gerrard, Bob McGoldrick, Hichem Ben Frej, George Peck, Steve Durand, Jon Romney, Craig Walker, Mike Revnell, Walter Brisken, Keith Morris, Jim Jackson, Miguel Guerra, Matt Luce CASPER KAT

The Very Long Baseline Array 3

VLB A Current IF Processing 4 Four IFs – Eight sidebands – 2 sidebands (upper/lower) per IF – 16MHz per sideband – 128 Mbps peak data rate

VLBA Upgraded IF Processing 5 Single sideband Up to Four IFs – 512MHz per IF – 4x128MHz sub-bands per IF – 16 total down-converters per DBE – 4096Mbps peak data rate

DBE Hardware: Overview 6

DBE Framework/Infrastructure 7

Synthesizer/Clock Distribution Board Inputs – 5MHz reference (Maser) – GPS 1 PPS Outputs: – 1024MHz (3 copies) 1.5 o RMS phase noise – 1 PPS (4 copies) Buffers ALC control signals from ROACH

Automated Level Control (ALC) Gain: -11dB to +20dB in 1dB steps Optional 20dB fixed attenuator 2 channels

ALC-Bandpass variation

ALC Delay variation

Anti-aliasing filter amplitude

Anti-aliasing filter: band edges

Anti-aliasing filter: stopband

Anti-aliasing filter: phase

DBE Framework/Infrastructure 16 Blue boxes are Haystack specific and will be replaced in the DDC personality

DDC: Block Diagram 17

ALC: Raw sample capture Accepts de-multiplexed samples from both ADC channels Selectable IF0/IF1 capture Output sample stream: – Up to time continuous samples of the raw ADC data Two access methods: – File – Network socket 18

ALC: Raw sample capture examples 19

ALC: Power setting loop 20 Relative Power – V rms to dBm – Adjust ALC linearly in dB

GUI: Device Browser, Matrix Switch

GUI: Device Browser, DBE

GUI: Monitor archive query tool 23

GUI: Monitor archive data

Results 1: Autocorrelation on LA 25

Results II: 0 Baseline Cross-correlation 26

Questions? 27

ALC Adjustment Range Nominal Input power to the DBE: -33dBm. 28 ALC Control Value Sampler Input power level RMS CountsSampler Head Room dBm3220dB dBm2322.5dB dBm1626dB dBm9.530dB dBm3.340dB

DDC: Specifications As per the VLBA sensitivity upgrade project book, the filters in the DDC personality must conform to the following: – Quantity:Eight DDCs per 512MHz wide channel – Tunable range:Within the 512MHz wide channel – Minimum tuning step:1 Hz (center frequency specified). – Output truncation: Any number of bits between 1 and 8. – Decimated output rate: 128 kbits/s – 2048 Mbits/s. – Return to previous phase after switching to another frequency/bandwidth and back. 29