DDF is the distribution equipment used between digital multiplexers, between digital multiplexer and exchange equipment or non voice service equipment, carrying out such functions as cables connection, cable patching and test of loops that transmitting digital signals. All parameters and performance indexes of 75 ohm MPX 272 and 120ohm MPX 286 series DDF complies with YD/T779-1999 Digital Distribution Frame. Working conditions: Working temperature: -5℃~+40℃ Relative humidity: ≤85% (+30℃) Atmospheric pressure: 70kPa~106kPa Storage temperature: -25℃~+55℃ Electrical performance Performance Indexes Working rate a) 2Mbit/s, 8Mbit/s, 34Mbit/s, 45Mbit/s, 140Mbit/s, 155Mbit/s; b) 2Mbit/s, 8Mbit/s, 34Mbit/s (Only suitable for coaxial connector whose diameter of inner conductor is 1.24mm or for the connector with approximate structure) Characteristic impedance 75ohm Contact resistance For external conductor≤2.5mΩ, increment after mechanical durability and salt-fog test ≤2.5mΩ For internal conductor≤5mΩ,increment after mechanical durability and salt-fog test ≤5mΩ Insulation resistance The insulation resistance between external and internal conductor of coaxial connector, and between internal conductor and metal parts of unit≥1000MΩ, and the DC voltage of the test loop is 500V±50V Dielectric strength It can withstand the test with no breakdown and arcing under the exerted voltage of 1000V AC (rms) of 50Hz for one minute, between inner and outer conductor of coaxial connector, and between inner conductor and metal parts of unit. Crosstalk ratio a) ≥70 dB (50kHz~233 kHz) b) ≥70 dB (50kHz~51 kHz) (Only suitable for coaxial connector whose diameter of internal conductor is 1.24mm or the connector with approximate structure) Insertion loss a) ≤0.3 dB (50kHz~233 kHz) b) ≤0.3 dB (50kHz~51 kHz) (Only suitable for coaxial connector whose diameter of internal conductor is 1.24mm or the connector with approximate structure) Return loss a) ≥18 dB (50kHz~233 kHz) b) ≥18 dB (Only suitable for coaxial connector whose diameter of internal conductor is 1.24mm or the connector with approximate structure)