The 478A Thermistor Mount is an RF power sensor head that is compatible with the 431 and 432 series RF power meters. Its frequency range is 10 MHz to 10 GHz, and its power range is -30 dBm to 10 dBm. Maximum power is not to exceed 30 mW (+15 dBm) average power or 5 W*microsecond energy. It has a Type N male input connector. Introduced in 1961, it is still produced and sold by Keysight today.