A radar level gauge system for determining a filling level of a product in a tank, said radar level gauge system comprising: a microwave signal source controllable to generate an electromagnetic transmit signal (S T) with a time-varying frequency; a propagation device connected to said microwave signal source and arranged to propagate said electromagnetic transmit signal towards a surface of said product in the tank, and to propagate an electromagnetic surface echo signal (S R) resulting from reflection of said transmit signal at said surface back from said surface; a mixer connected to said microwave signal source and to said propagating device and configured to mix said transmit signal and said surface echo signal to form a mixer signal; sampling circuitry connected to said mixer for sampling said mixer signal to provide sampled values of the mixer signal; first timing signal generating circuitry connected to said microwave signal source and to said sampling circuitry for providing first timing signals to said microwave signal source and to said sampling circuitry; signal processing circuitry for determining said filling level based on said sampled values of the mixer signal; second timing signal generating circuitry connected to said signal processing circuitry for providing second timing signals to said signal processing circuitry; and measurement control circuitry for controlling the radar level gauge system between a measurement state in which said first timing signal generating circuitry is enabled and a signal processing state in which said first timing signal generating circuitry is disabled, wherein: in said measurement state, said measurement control circuitry: controls said microwave signal source to generate said transmit signal with said time-varying frequency being related to said first timing signals from said first timing signal generating circuitry; and controls said sampling circuitry to sample said mixer signal at sampling times related to said first timing signals from said first timing signal generating circuitry; and in said signal processing state, said measurement control circuitry: controls said signal processing circuitry to determine said filling level based on said sampled values of the mixer signal using said second timing signals from said second timing signal generating circuitry. a microwave signal source controllable to generate an electromagnetic transmit signal (S T) with a time-varying frequency; a propagation device connected to said microwave signal source and arranged to propagate said electromagnetic transmit signal towards a surface of said product in the tank, and to propagate an electromagnetic surface echo signal (S R) resulting from reflection of said transmit signal at said surface back from said surface; a mixer connected to said microwave signal source and to said propagating device and configured to mix said transmit signal and said surface echo signal to form a mixer signal; sampling circuitry connected to said mixer for sampling said mixer signal to provide sampled values of the mixer signal; first timing signal generating circuitry connected to said microwave signal source and to said sampling circuitry for providing first timing signals to said microwave signal source and to said sampling circuitry; signal processing circuitry for determining said filling level based on said sampled values of the mixer signal; second timing signal generating circuitry connected to said signal processing circuitry for providing second timing signals to said signal processing circuitry; and measurement control circuitry for controlling the radar level gauge system between a measurement state in which said first timing signal generating circuitry is enabled and a signal processing state in which said first timing signal generating circuitry is disabled, wherein: in said measurement state, said measurement control circuitry: controls said microwave signal source to generate said transmit signal with said time-varying frequency being related to said first timing signals from said first timing signal generating circuitry; and controls said sampling circuitry to sample said mixer signal at sampling times related to said first timing signals from said first timing signal generating circuitry; and in said measurement state, said measurement control circuitry: controls said microwave signal source to generate said transmit signal with said time-varying frequency being related to said first timing signals from said first timing signal generating circuitry; and controls said sampling circuitry to sample said mixer signal at sampling times related to said first timing signals from said first timing signal generating circuitry; and in said signal processing state, said measurement control circuitry: controls said signal processing circuitry to determine said filling level based on said sampled values of the mixer signal using said second timing signals from said second timing signal generating circuitry.