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Disciplined Oscillators Keep Time in Small Satellites

Dec. 8, 2020
These compact oscillators use PLL-type techniques to improve the stability of crystal oscillators with disciplining from GPS receivers, serving the needs of LEOS systems.

Timing is everything, especially for navigation systems, and disciplined oscillators (DOs) typical provide the positive navigation and timing (PNT) in satellite systems. By combining quartz-crystal DOs with GPS satellites via a tracking loop, it is possible to achieve even better timing than with either approach alone. GPSDOs, also known as GPS clocks, deliver the accuracy needed to maintain precise nanosecond timing in low-power applications such as low-earth-orbit satellites (LEOS), cube satellites and passive radar systems.

The long-term frequency stability or Allan deviation of the GPS receiver portion of a GPSDO is outstanding, although its short-term stability may be degraded by a few factors, including the resolution of the reference timing circuits, signal propagation effects from the satellite and atmospheric conditions. To overcome the degradation of short-term stability, the Hyas GPSDOs from Bliley Technologies achieve ±10 ppb holdover stability with −150 dBc/Hz phase noise offset 10 Hz from a 10-MHz carrier when running on 2.25 W steady-state power (and less than 3 W startup power). These high-performance sources feature amplitude-balanced outputs within ±0.5 dB and phase-balanced outputs within ±3 deg. in a package that measures just 1.35 × 3.35 × 0.815 in. (34.3 × 85.1 × 20.7 mm) and weighs less than 175 g.

Designed for low-power systems, the Hyas master reference oscillators (MROs) provide the opportunity to extend GPSDO technology to a greater number of small satellite applications, such as communications, earth observation, and tracking. “By combining OCXO short-term stability and long-term stability achieved by GPS disciplining, our Hyas product provides high precision frequency stability along with multiple amplitude and phase balanced frequency reference signals to coherently feed into multiple payloads onboard small satellites. Its form factor allows for ease of integration onboard cube satellites.” says Darshan Shah, director of Business Development for Space Products of Bliley Technologies.

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