a mixer includes a first terminal and a second terminal forming a first input port for receiving a first signal having a first frequency ; a second input port for receiving a second signal having a second frequency ; a mixer output port for a resulting signal ; a first group of valves having their control inputs coupled to the first terminal for receiving the first signal ; a second group of valves having their control inputs coupled to the second terminal for receiving the first signal ; and a third group of two valves having their control inputs coupled for receiving the second signal . the valves co - operate such that in operation the mixer produces the resulting signal responsive to the first and second signals . the mixer also includes at least one passive low pass filter having an inductor , the low pass filter being connected to the control input of a valve in the first and second groups .