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hmc451lc3 output pin impedance in dc is below 10 ohm

hi,i have evaluation board of hmc451lc3 and when i measure  the output pin of this amplifier  regarding to gnd pin with ohm meter i see the impedance below 10 ohm and when just power up the amplifier i see the output rf pin has 4 volt difference to gnd even though there is no input frequency injected. i see that this amplifier is ac coupled so why i see this voltage .the board that i have is 111665 Evaluation PCB  eval-hmc451lc3?best regards.Best regards