A radar level gauge system for determining a filling level of a product contained in a tank, the radar level gauge system comprising: first pulse generating circuitry for generating a transmission signal in the form of a first pulse train having a first pulse repetition frequency, second pulse generating circuitry for generating a reference signal in the form of a second pulse train; frequency control circuitry for controlling the second pulse generating circuitry to generate said second pulse train with a second pulse repetition frequency, the second pulse repetition frequency differing from the first pulse repetition frequency by a predetermined frequency difference; a propagation device connected to the first pulse generating circuitry and arranged to propagate the transmission signal towards a surface of the product inside the tank, and to return a reflected signal resulting from reflection of the transmission signal at the surface of the product contained in the tank; measurement circuitry connected to the propagation device and to the second pulse generating circuitry, the measurement circuitry being configured to form a measurement signal based on the reflected signal and the reference signal; and processing circuitry connected to the measurement circuitry for determining a value indicative of the filling level based on the measurement signal, wherein said radar level gauge system further comprises: first frequency selection circuitry connected to said first pulse generating circuitry and said frequency control circuitry and configured to provide a higher order harmonic frequency component of said transmission signal to said frequency control circuitry; and second frequency selection circuitry connected to said second pulse generating circuitry and said frequency control circuitry and configured to provide a higher order harmonic frequency component of said reference signal to said frequency control circuitry, said frequency control circuitry being configured to control said second pulse generating circuitry based on said higher order harmonic frequency component of the transmission signal and said higher order harmonic frequency component of the reference signal. first pulse generating circuitry for generating a transmission signal in the form of a first pulse train having a first pulse repetition frequency, second pulse generating circuitry for generating a reference signal in the form of a second pulse train; frequency control circuitry for controlling the second pulse generating circuitry to generate said second pulse train with a second pulse repetition frequency, the second pulse repetition frequency differing from the first pulse repetition frequency by a predetermined frequency difference; a propagation device connected to the first pulse generating circuitry and arranged to propagate the transmission signal towards a surface of the product inside the tank, and to return a reflected signal resulting from reflection of the transmission signal at the surface of the product contained in the tank; measurement circuitry connected to the propagation device and to the second pulse generating circuitry, the measurement circuitry being configured to form a measurement signal based on the reflected signal and the reference signal; and processing circuitry connected to the measurement circuitry for determining a value indicative of the filling level based on the measurement signal, wherein said radar level gauge system further comprises: first frequency selection circuitry connected to said first pulse generating circuitry and said frequency control circuitry and configured to provide a higher order harmonic frequency component of said transmission signal to said frequency control circuitry; and second frequency selection circuitry connected to said second pulse generating circuitry and said frequency control circuitry and configured to provide a higher order harmonic frequency component of said reference signal to said frequency control circuitry, said frequency control circuitry being configured to control said second pulse generating circuitry based on said higher order harmonic frequency component of the transmission signal and said higher order harmonic frequency component of the reference signal. first frequency selection circuitry connected to said first pulse generating circuitry and said frequency control circuitry and configured to provide a higher order harmonic frequency component of said transmission signal to said frequency control circuitry; and second frequency selection circuitry connected to said second pulse generating circuitry and said frequency control circuitry and configured to provide a higher order harmonic frequency component of said reference signal to said frequency control circuitry, said frequency control circuitry being configured to control said second pulse generating circuitry based on said higher order harmonic frequency component of the transmission signal and said higher order harmonic frequency component of the reference signal.