ADC Crosstalk Measurements with SNAP for OVRO-LWA

Abstract

The LWA (Long-Wavelength Array), located at Owens Valley Radio Observatory, is a powerful and sensitive radio telescope. OVRO-LWA needs very good signal transmission with minimal spurious emissions carried through its signal chain. The telescope receives analog radio signals from space, then interprets them as digital data that can be computationally analyzed to gain a better understanding of what that data means. A high-level description of the flow of information in the LWA is as follows: Analog receiver → analog-to-digital conversion (ADC) → short-timescale FPGA processing → long-timescale GPU processing In order to minimize unwanted effects, some parts of the signal chain are being redesigned. This includes possible changes in the ADCs employed, the FPGA used, or the circuitry linking the two. A variety of options are available for the new hardware, including several boards from the CASPER1 collaboration. Currently, the LWA uses CASPER ADC16x250-8 RJ45 rev 1 boards with HMCAD1511 ADC chips. A different CASPER board, or a new combination of ADC and FPGA hardware from multiple platforms, may be used. Among the candidate replacement boards is SNAP2 (Smart Network ADC Processor). In order to determine the viability of retooling the SNAP board for this purpose, the performance characteristics of its ADC hardware have been tested.