This chapter discusses the use of filters, other components in frequency modulation (FM) combiners, and the hardware used to combine an in-band-on-channel digital signal into an analog signal. It also discusses combining the digital and analog signals from separate transmitters into a common transmission line before sending them to the antenna. The chapter examines the fundamentals of combining and the use of combiners in FM broadcasting. Transmitting several frequencies from a single broadband antenna system requires the use of a combining system, or combiner, composed of radiofrequency filters and interconnecting transmission line. Combiners are often made up of multiple elements that as a system provide the desired results. The method of combining analog and digital is normally used for stations that only have one single-input antenna and an analog transmitter with the reserve capacity to make up for the 10% loss in power.