Fire alarm signalling with voice modulated HF signal multiplexed on to plateaus of existing lower frequency pulses carried on power cabling

摘要

A signal for use on a wired network interconnecting electronic devices, such as loudspeakers and detectors in an alarm network, comprising: a base voltage for conveying power to the devices; a pulsed voltage signal bearing coded information for transfer between the electronic devices; and a digital signal (901, 902) superimposed onto selected portions of the pulsed voltage signal, where the digital signal comprises a carrier signal modulated by a data signal for transfer between the electronic devices. This is used in fire alarm networks, for example, to convey multimedia such as audio, voice or other data such as control signals. A fire detector having a microphone for monitoring the surrounding sound level and a controller for adjusting the sound level from a loudspeaker in dependence of the surrounding sound level.