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We report the results of a bilateral comparison of attenuation measurements between the National Physical Laboratory (NPLI, New Delhi) and the Standards and Calibration Laboratory (SCL, Hong Kong), carried out under the Asia-Pacific Metrology Programme. Commercial 50 coaxial attenuators (in APC-7 connectors), of nominal attenuation values 3 dB, 10 dB and 20 dB, were calibrated at 30 MHz, 5 GHz and 10 GHz against the 30 MHz standard WBCO attenuators of both laboratories. A direct 30 MHz series-substitution technique and a 30 MHz intermediate-frequency substitution technique were employed at the NPLI to calibrate attenuators at 30 MHz and microwave frequencies using a VM-3 attenuator and signal calibrator, respectively. The same techniques were used at the SCL in association with a vector signal analyser (HP-89441A). The expanded uncertainty as measured at the NPLI, quoted at the 95 % confidence level for the attenuation range 3 dB to 20 dB, varies from 0.007 dB to 0.015 dB at 30 MHz, 0.017 dB to 0.032 dB at 5 GHz, and 0.020 dB to 0.037 dB at 10 GHz. The uncertainty reported by the SCL for the same attenuation range is approximately 0.010 dB at 30 MHz and varies from 0.010 dB to 0.016 dB at 5 GHz, and 0.016 dB to 0.023 dB at 10 GHz. The mean values of the measured attenuation of both laboratories were found to lie within the quoted limits of the uncertainties.

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