Incoherent clocking for radio telescopes

The method of “incoherent clocking” is discussed, wherein all-digital methods using FPGAs and COTS digital fiberoptic modules and commercial (e.g. aerial) fiber routing, along with free-running local oscillators at each antenna, are used to provide a clock and timing solution for “at antenna” digitization for any cost, scale, and frequency of radio telescope. Antenna local oscillator stability (Allan Deviation) requirements are developed, indicating there is virtually no limit in baseline extent that can be handled with this method. Research results and plans, focusing on a hardware “laboratory demonstrator” at 10 Gbps using a Xilinx ZCU111 evaluation board, with external real-world aerial fiber up to 300 km with OEO repeaters, are presented and discussed. As well, although not discussed in this paper, with NRC “Small Teams” funding, 4 antennas of the NRC-Penticton 7-antenna 400-1800 MHz Synthesis Telescope are being outfitted with new feeds, receivers, an at-antenna digitizer, and a “TALON Demonstration Correlator” (developed for the SKA) to test this method on-the-sky.