A level gauge using microwaves to determine a distance to a surface of a product in a tank, comprising: a microwave source arranged to generate a measurement signal, comprising a first frequency sweep, and a second frequency sweep, a signal propagation device, connected to the microwave source and adapted to allow propagation of the measurement signal into the tank, and to receive an echo signal reflected from said surface, a power store to power the microwave source, said power store being charged between sweeps, a mixer connected to said microwave source and said signal propagation device, and arranged to mix said measurement signal with said echo signal to form a first intermediate frequency, IF, signal based on said first frequency sweep, and a second IF signal based on said second frequency sweep, processing circuitry, connected to receive said IF signals from said mixer and adapted to sample said first IF signal and said second IF signal, to form a combined sample vector including samples from each IF signal, and to determine said distance based on said combined sample vector, wherein each frequency sweep includes a set of discrete frequencies, whereby each IF signal is piecewise constant, wherein said processing circuitry is adapted to update said combined sample vector after each frequency sweep, by combining samples from a most recently acquired IF signal with samples of a second most recently acquired IF signal, and wherein a) the two sweeps are interleaved with each other, or b) the first frequency sweep starts at f0 and includes N steps of size Δf and the second frequency sweep starts at f0+NΔf and also includes N steps of size Δf. a microwave source arranged to generate a measurement signal, comprising a first frequency sweep, and a second frequency sweep, a signal propagation device, connected to the microwave source and adapted to allow propagation of the measurement signal into the tank, and to receive an echo signal reflected from said surface, a power store to power the microwave source, said power store being charged between sweeps, a mixer connected to said microwave source and said signal propagation device, and arranged to mix said measurement signal with said echo signal to form a first intermediate frequency, IF, signal based on said first frequency sweep, and a second IF signal based on said second frequency sweep, processing circuitry, connected to receive said IF signals from said mixer and adapted to sample said first IF signal and said second IF signal, to form a combined sample vector including samples from each IF signal, and to determine said distance based on said combined sample vector, wherein each frequency sweep includes a set of discrete frequencies, whereby each IF signal is piecewise constant, wherein said processing circuitry is adapted to update said combined sample vector after each frequency sweep, by combining samples from a most recently acquired IF signal with samples of a second most recently acquired IF signal, and wherein a) the two sweeps are interleaved with each other, or b) the first frequency sweep starts at f0 and includes N steps of size Δf and the second frequency sweep starts at f0+NΔf and also includes N steps of size Δf. a) the two sweeps are interleaved with each other, or b) the first frequency sweep starts at f0 and includes N steps of size Δf and the second frequency sweep starts at f0+NΔf and also includes N steps of size Δf.