A guided wave radar level gauge for determining the filling level of product in a tank, said gauge comprising: a housing providing explosion proof protection, and being electrically connected to a housing ground potential, an explosion proof first signal passage in said housing wall, said first signal passage configured to be connected to an external power supply, an explosion proof second signal passage in said housing wall, said second signal passage providing an intrinsically safe, IS, output, a resistor having a first terminal connected to the IS output and a second terminal connected to the housing ground potential, a transmission line probe connected to said IS output, said probe being adapted to direct a microwave transmit signal toward said product and return reflections thereof from a surface of said product, wherein said housing encloses: radar level gauge, RLG, circuitry (14, 15, 16, 17), a microwave unit connected to the IS output, said microwave unit configured to generate and transmit an microwave transmit signal S T and receive a microwave return signal S R reflected from the tank, said RLG circuitry (14, 15, 16, 17) and said microwave unit having a floating ground potential which is independent from said housing ground potential, and a set of blocking capacitors connected between the microwave unit and the IS output, which blocking capacitors serve to block any DC components, wherein the microwave unit includes: a pulse generator having a first terminal connected to said IS output via said set of blocking capacitors, and a second terminal connected to said housing ground potential via said set of blocking capacitors, and a differential receiver, having a first terminal connected to said IS output via said set of blocking capacitors, and a second terminal connected to said housing ground potential via said set of blocking capacitors, a voltage between said first and second terminals forming an input signal to said differential receiver. a housing providing explosion proof protection, and being electrically connected to a housing ground potential, an explosion proof first signal passage in said housing wall, said first signal passage configured to be connected to an external power supply, an explosion proof second signal passage in said housing wall, said second signal passage providing an intrinsically safe, IS, output, a resistor having a first terminal connected to the IS output and a second terminal connected to the housing ground potential, a transmission line probe connected to said IS output, said probe being adapted to direct a microwave transmit signal toward said product and return reflections thereof from a surface of said product, radar level gauge, RLG, circuitry (14, 15, 16, 17), a microwave unit connected to the IS output, said microwave unit configured to generate and transmit an microwave transmit signal S T and receive a microwave return signal S R reflected from the tank, said RLG circuitry (14, 15, 16, 17) and said microwave unit having a floating ground potential which is independent from said housing ground potential, and a set of blocking capacitors connected between the microwave unit and the IS output, which blocking capacitors serve to block any DC components, a pulse generator having a first terminal connected to said IS output via said set of blocking capacitors, and a second terminal connected to said housing ground potential via said set of blocking capacitors, and a differential receiver, having a first terminal connected to said IS output via said set of blocking capacitors, and a second terminal connected to said housing ground potential via said set of blocking capacitors, a voltage between said first and second terminals forming an input signal to said differential receiver.