Interference between frequency hopping (FH) systems sharing the same frequency band can decrease the communication performance. The decrease can be severe, especially for systems on the same platform or in the vicinity of each other. Interference can stem both from sharing the same frequency channel momentarily or from adjacent channels. It is shown that a devastating high error floor can appear when several FH systems are using the same frequency band and special considerations on the system coexistence are overlooked. Here, the effects on the communication system is shown both with and without adjacent channel interference. Some strategies to decrease the effects of interference, i.e. optimal sequences and isolation, are also evaluated and discussed.