| 摘要 |
In this communication system, which contains a battery-fed control device to which the microphones and receivers, in each case accommodated in the protective helmets of the travelling persons and which provide for a voice connection between the travelling persons, can be connected, the influence of the travelling noise on the intelligibility of speech is to be effectively eliminated with a minimum of expenditure and, in addition, it should be possible to use the communication system for additional, mutually independent supplementary functions. This is made possible by the fact that a separate microphone for continuously picking up the travelling noise is allocated to the control device. This microphone is followed by a circuit arrangement for converting the travelling noise into a direct voltage proportional to this noise, which is used as control voltage for continuously adapting the operating threshold of a threshold switch connected to the helmet microphones to the travelling noise level in such a manner that the threshold switch distinguishes between this noise level and the useful signals and only switches through the useful signals supplied via the helmet microphones to the output amplifier via an electronic switch, and that the direct voltage proportional to the travelling noise is at the same time used as control voltage for the noise-dependent volume control of supplementary devices which can be optionally connected to the control device, in such a manner that it continuously controls the gain of an amplifier following the supplementary devices and preceding the output amplifier for the receivers.
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