A radar level gauge system for determining a filling level of a product in a tank, comprising: a transceiver for generating, transmitting and receiving electromagnetic signals; a signal propagation device coupled to the transceiver for propagating a transmit signal (S T) towards a surface of said product, and for propagating a surface echo signal (S R) resulting from reflection of said transmit signal at said surface back towards said transceiver; and processing circuitry coupled to said transceiver for determining said filling level based on a relation between said transmit signal and said surface echo signal, said transceiver comprising: PLL circuitry for generating an output signal, said PLL circuitry being configured to indicate a lock state of said PLL circuitry; and signal modifying circuitry connected to said PLL circuitry for receiving said output signal and for modifying at least one property of said output signal to form said transmit signal, characterized in that: said signal modifying circuitry is controllable between a first signal modifying state resulting in a first modification by said signal modifying circuitry of said at least one property of said output signal, and a second signal modifying state resulting in a second modification by said signal modifying circuitry of said at least one property of said output signal, different from said first modification, and said signal modifying circuitry is arranged and configured to receive a PLL status signal (STATUS) indicative of said lock state of the PLL circuitry, and to transition from said first signal modifying state to said second signal modifying state in response to said PLL status signal indicating that said PLL circuitry is in a locked state. a transceiver for generating, transmitting and receiving electromagnetic signals; a signal propagation device coupled to the transceiver for propagating a transmit signal (S T) towards a surface of said product, and for propagating a surface echo signal (S R) resulting from reflection of said transmit signal at said surface back towards said transceiver; and processing circuitry coupled to said transceiver for determining said filling level based on a relation between said transmit signal and said surface echo signal, said transceiver comprising: PLL circuitry for generating an output signal, said PLL circuitry being configured to indicate a lock state of said PLL circuitry; and signal modifying circuitry connected to said PLL circuitry for receiving said output signal and for modifying at least one property of said output signal to form said transmit signal, characterized in that: said signal modifying circuitry is controllable between a first signal modifying state resulting in a first modification by said signal modifying circuitry of said at least one property of said output signal, and a second signal modifying state resulting in a second modification by said signal modifying circuitry of said at least one property of said output signal, different from said first modification, and said signal modifying circuitry is arranged and configured to receive a PLL status signal (STATUS) indicative of said lock state of the PLL circuitry, and to transition from said first signal modifying state to said second signal modifying state in response to said PLL status signal indicating that said PLL circuitry is in a locked state. PLL circuitry for generating an output signal, said PLL circuitry being configured to indicate a lock state of said PLL circuitry; and signal modifying circuitry connected to said PLL circuitry for receiving said output signal and for modifying at least one property of said output signal to form said transmit signal, characterized in that: said signal modifying circuitry is controllable between a first signal modifying state resulting in a first modification by said signal modifying circuitry of said at least one property of said output signal, and a second signal modifying state resulting in a second modification by said signal modifying circuitry of said at least one property of said output signal, different from said first modification, and said signal modifying circuitry is arranged and configured to receive a PLL status signal (STATUS) indicative of said lock state of the PLL circuitry, and to transition from said first signal modifying state to said second signal modifying state in response to said PLL status signal indicating that said PLL circuitry is in a locked state. said signal modifying circuitry is controllable between a first signal modifying state resulting in a first modification by said signal modifying circuitry of said at least one property of said output signal, and a second signal modifying state resulting in a second modification by said signal modifying circuitry of said at least one property of said output signal, different from said first modification, and said signal modifying circuitry is arranged and configured to receive a PLL status signal (STATUS) indicative of said lock state of the PLL circuitry, and to transition from said first signal modifying state to said second signal modifying state in response to said PLL status signal indicating that said PLL circuitry is in a locked state.