A user can not access, but they have been tested and is up-47dB signal is down 48dB

What is the reason?

47db?? Heard db (Dolby) is a unit of volume ~ Oh one user can not access, But they have been tested and is up-47dB downlink signal is also very low noise 48dB
to
Lou Dong-ray machine is linked directly, without intermediate amplifiers.The whole district a total of three
-ray machines have been tested one of the -Ray machine a little unusual, his noise in the 35 ~ 50Mhz high but not with Taiwan that the user does not have an expert
under the guidance Why is there such a situation?