InfiniiMax III Differential Probe Head 28GHz, 2.92mm, The Agilent (now Keysight) is an InfiniiMax Differential Probe Head with a bandwidth of 28 GHz. Bandwidth: 28 GHz Input impedance: DC Input impedance resistance: 55 ohms to V therm Input resistance 10 kHz: 50 ohms to 0.909 x V therm Input voltage range: Input voltage range: 2.5 V rms Input common mode range: +/- 12 V DC to 250 Hz, +/- 2.5 V > 250 Hz (must not exceed max input voltage)