Satellites of Opportunity as Calibration Sources: Peak- Timing Pointing and Thermal-Node LO Drift

Abstract

Low Earth orbit constellations put a predictable Ku-band beacon through a fixed dish beam several times an hour, and that makes them a calibration source available to almost any station. I use those crossings to calibrate a 4.5 m Earth Station dish, with no dedicated beacon, radio star or boresight tower. Each scheduled stare yields one power-transient peak time. For a circular Gaussian beam, each peak time gives one linear constraint, on the beam center and a common clock offset. The track geometry comes from SGP4 and public CelesTrak supplemental GP elements. From 138 Starlink and OneWeb stares over 35 hours, the least-squares solution places the beam at azimuth 341.608° and elevation 70.309°, with leave-one-out jackknife deviations of 0.035° cross-elevation and 0.021° in elevation, and τ = 0.007 ± 0.026 s. The same transits also give a 0.589° beamwidth, a Starlink identity test from the OFDM cyclic prefix, and a frequency reference that exposes a sun-driven LNB drift of about −0.14 ppm/°C. The method needs only a fixed dish, a wideband receiver that records time-stamped power, and published ephemerides. It returns pointing, a clock check and oscillator drift from routine operation rather than a dedicated calibration campaign. In my view, it suits any narrow-beam ground station that has to know where it is looking, before it can trust what it is recording.