Radial-velocity observations spanning more than a century are used to produce a reliable orbit of the {delta} Sagittae system. We find an orbital period of 3703.7+/-1.5 d and a semi-amplitude of 7.73+/-0.05 km/s. In addition, we find quasi-periodic variations with time-scales in the range of 550-750 d and a typical amplitude of 1 km/s. The phase and amplitude are both irregular, sometimes changing very abruptly. We consider pulsation, rotational modulation and convection as possible causes of the variations, finally favouring convection.