Abstract: Portable, plugable electrical test equipment signals the presence or absence of radio frequency energy within a predetermined frequency spectrum, as on a CATV or MATV video distribution system. The equipment comprises a cascaded bandpass filter, radio frequency amplifier, coupling-detector network, and operational amplifier to selectively energize a light emitting diode when a sufficient level of energy in the requisite frequency range is sensed.In accordance with one aspect of the present invention, the coupling-detector network includes circuitry for quiescently biasing the inverting and noninverting inputs of the operational amplifier to a state such that the LED is not activated. The circuitry further includes as an integral part thereof detector structure for reversing the relative potential amplitudes impressed on the amplifier inputs when a sufficient quantum of the subject radio frequency energy is coupled to the composite test equipment, such that an appropriate output indication is generated.