Values expressed in dBmV that are preceded by a minus sign (-) represent what?

Values expressed in dBmV represent a decibel measurement of voltage relative to 1 millivolt across a standard impedance of 75 ohms. When a dBmV value is preceded by a minus sign, it indicates that the voltage level is below the reference level of 1 millivolt. Specifically, a negative dBmV value implies that the actual voltage is less than 1 millivolt when measured across 75 ohms.

In practical terms, for instance, if a dBmV reading is -10 dBmV, it can be calculated that the voltage level is now 0.316 millivolts (since -10 dBmV corresponds to approximately 0.316 mV across 75 ohms). This reinforces that the signal being measured is indeed less than the reference voltage of 1 millivolt.

Understanding this relationship is crucial for technicians as they assess signal levels and troubleshoot issues within cable systems, ensuring effective communication and service delivery.