  We present a proof-of-concept experiment to realize microwave primary power
standard with a true-twin microcalorimeter. Double feeding line
microcalorimeters are widely used by National Metrology Institutes. A drawback
concerns the system calibration: traditional processes changes measurement
conditions between system characterization and the measurement stage.
Nevertheless, if the feeding lines are made twin, a measurement scheme that
avoids separate characterization can be applied, equations simplify and time
consumption is halved. Here we demonstrates the feasibility of the idea. The
result of an effective efficiency spectroscopy of a thermoelectric power sensor
is compared with figures obtained with well established methods.
