The National Instruments USB-5681 RF Power Sensor (Part Number: 781214-01) is a compact and highly precise instrument designed for mobile applications requiring accurate RF power measurements. This device operates in both hardware and software-triggered modes, making it versatile for various testing environments. It supports a broad frequency range from 10 MHz to 18 GHz and can handle input signal strengths between -40 dBm and +20 dBm, categorized into two measurement sub-ranges: +20 dBm to -7 dBm and -7 dBm to -40 dBm. The USB-5681 offers a bandwidth support of 50 kHz with a measurement speed of 100 samples per second, all while maintaining a typical linearity uncertainty of less than 3%. Adhering to safety standards such as IEC 61010-1, EN 61010-1, UL 61010-1, and CSA C22.2 No. 61010-1, the device operates with a 5 VDC input from a USB host, drawing 450 mA of current. With built-in protection against a maximum voltage of ±20 VDC and absolute power of +30 dBm at the RF port, the USB-5681 is engineered for reliability. The device weighs 0.51 lb (230 g) and, when the RF connector and silicone cover are removed, measures 25 mm × 45 mm × 110 mm. It is designed to function within an operating temperature range of 0 to 50 °C and a storage temperature range of -40 °C to +71 °C. Relative humidity conditions for operation vary with temperature, supporting a non-condensing humidity of 45% at 50 °C, 75% at 40 °C, and 95% at 30 °C. Although the USB-5681 has been declared obsolete by National Instruments, it remains available for purchase and repair through Apex Waves.