Signal Transport and RF over Fiber Design for ALPACA

• Main Author: Nygaard, Erich Johannes
• Format: Others
• Published: BYU ScholarsArchive 2020
• Subjects: radio astronomy; RF over fiber; phased array feeds; analog; radio frequency interference; Arecibo Telescope; Engineering
• Online Access: https://scholarsarchive.byu.edu/etd/8753; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=9753&context=etd

The design of the RF over fiber signal transport system for the ALPACA receiver is described, with particular attention to the strict noise requirements as well as dynamic range considerations. Also discussed are analytical tools for analyzing dynamic range in the context of RFI-rich radio astronomy observational settings, including formulas for maximum interference to noise ratios and a simulation framework for predicting distortion levels. Phase and gain stability measurements of the signal transport system are presented, including the effects of the multi-strand armored fiber optic cable. The resulting system meets design requirements, with equivalent noise temperature below 900 K in 90° F ambient air, resulting in less than 1 K contribution to the system noise temperature. Typical gain is 31-37 dB, and gain differences between channels are stable within 0.25 dB in 90° F conditions. Phase drift between channels due to electronics remains below 1° at room temperature, and below 1.3° in a warm environment. The fiber optic cable is predicted to cause phase changes between channels of no more than 1.3° per °C. Typical spurious free dynamic range is 99 dB·Hz^(⅔), and distortion levels for normal RFI conditions at Arecibo are expected to be 28 dB below the system noise floor.