This is a Keysight V8486A Waveguide Power Sensor. This unit is in GREAT condition, and guaranteed fully operational.  

The Agilent V8486A diode power sensor is designed for use with the EPM series, EPM-P series, 70100A, E1416A and the discontinued 43x power meters, and provides extraordinary accuracy and stability. The V8486A power sensor gives you low SWR and is traceable to the U.S. National Institute of Standards and Technology (NIST). A 50 MHz calibration port is included with the power sensor. This calibration eliminates the uncertainties due to temperature changes and the variance in making measurements with different meter/sensor combinations.

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Shipping in the USA is $30.