Thirty dB coupling takes a thousandth of the through power, leaving the main line as close to undisturbed as a coupler allows. It is the configuration to specify where the coupler remains in the path during a calibrated measurement, or where a 20 dB tap would exceed the input rating of the instrument at the coupled port. Coupling is 29 dB minimum, 30 dB typical and 32 dB maximum across the full 8 to 40 GHz span, with 13 dB directivity and 0.5 dB minimum insertion loss on the through path. The body is longer than the tighter configurations at 47 x 33 x 11 mm (1.85 x 1.30 x 0.43 in), which the extended coupled section requires, though mass is unchanged at 30 g. Connectors are 2.92 mm female throughout, rated -40 to +85 °C operating and -70 to +100 °C storage. DC-BB-001 and DC-BB-002 provide 10 dB and 20 dB coupling in the same electrical family, so values can be mixed in one chain without introducing a second connector standard.