An RFSoC-based Backend and Timing System for the Balloon-borne Very Long Baseline Interferometry Experiment
Abstract
We present the design and performance characterization of the digital backend and precision-timing system for the Balloon-borne Very Long Baseline Interferometry Experiment (BVEX), a pathfinder for high-frequency stratospheric VLBI at 22 GHz. The backend uses one of the four 14-bit analog-to-digital converter inputs on an AMD-Xilinx RFSoC 4x2. Although the converters support sampling rates up to 5 GSPS, the flight configuration digitizes the 2-4 GHz intermediate frequency at 4.096 GSPS. CASPER firmware provides both a high-resolution spectrometer for pointing and receiver verification, and a VLBI acquisition chain with two-bit requantization that records at a rate of about 8.2 Gbps. The timestamped data packets are sent over 100 Gigabit Ethernet (GbE) to a 16 TB NVMe array in a storage computer that draws approximately 70-80 W. The timing chain uses a Rakon oven-controlled crystal oscillator as a timing reference while a time-interval counter measures its drift relative to a GPS reference with approximately 60 ps resolution. This is the first deployment of an RFSoC-based VLBI backend and precision-timing system on a stratospheric balloon. Ground tests validated the backend, spectrometer, and timing chain. The August 2025 CSA STRATOS flight ended before reaching the target float altitude because of a balloon failure, and as a result no science observations were obtained. For the planned 2027 reflight, we are developing a conduction-cooled data storage computer with 24 TB of NVMe capacity and a direct data path from the 100 GbE interface to the NVMe array.
Versions
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BibTeX
@misc{bagchi2026rfsocbased,
title = {{An RFSoC-based Backend and Timing System for the Balloon-borne Very Long Baseline Interferometry Experiment}},
author = {Mayukh Bagchi and Felix M. Thiel and Laura M. Fissel and Maggie Oxford and Lindy Blackburn and Rafael Costa and Vincent L. Fish and Daryl Haggard and Michael D. Johnson and Dominic W. Pesce and Ganesh Rajagopalan and Javier L. Romualdez and Aarchi Shah and Adrian K. Sinclair and Stephanie St-Jean and Terry Yang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11605},
eprint = {2609.11605},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.11605},
}
RIS
TY - UNPB
TI - An RFSoC-based Backend and Timing System for the Balloon-borne Very Long Baseline Interferometry Experiment
AU - Mayukh Bagchi
AU - Felix M. Thiel
AU - Laura M. Fissel
AU - Maggie Oxford
AU - Lindy Blackburn
AU - Rafael Costa
AU - Vincent L. Fish
AU - Daryl Haggard
AU - Michael D. Johnson
AU - Dominic W. Pesce
AU - Ganesh Rajagopalan
AU - Javier L. Romualdez
AU - Aarchi Shah
AU - Adrian K. Sinclair
AU - Stephanie St-Jean
AU - Terry Yang
PY - 2026
DA - 2026/09/10
PB - arXiv
DO - 10.48550/arxiv.2609.11605
UR - https://arxiv.org/abs/2609.11605
AB - We present the design and performance characterization of the digital backend and precision-timing system for the Balloon-borne Very Long Baseline Interferometry Experiment (BVEX), a pathfinder for high-frequency stratospheric VLBI at 22 GHz. The backend uses one of the four 14-bit analog-to-digital converter inputs on an AMD-Xilinx RFSoC 4x2. Although the converters support sampling rates up to 5 GSPS, the flight configuration digitizes the 2-4 GHz intermediate frequency at 4.096 GSPS. CASPER firmware provides both a high-resolution spectrometer for pointing and receiver verification, and a VLBI acquisition chain with two-bit requantization that records at a rate of about 8.2 Gbps. The timestamped data packets are sent over 100 Gigabit Ethernet (GbE) to a 16 TB NVMe array in a storage computer that draws approximately 70-80 W. The timing chain uses a Rakon oven-controlled crystal oscillator as a timing reference while a time-interval counter measures its drift relative to a GPS reference with approximately 60 ps resolution. This is the first deployment of an RFSoC-based VLBI backend and precision-timing system on a stratospheric balloon. Ground tests validated the backend, spectrometer, and timing chain. The August 2025 CSA STRATOS flight ended before reaching the target float altitude because of a balloon failure, and as a result no science observations were obtained. For the planned 2027 reflight, we are developing a conduction-cooled data storage computer with 24 TB of NVMe capacity and a direct data path from the 100 GbE interface to the NVMe array.
ER -