DAS Interface Trays (DIT) are an essential part of any fiber optic DAS system. These trays contain filters and amplifiers, and are responsible for conditioning the RF carrier signals for insertion into the remote Distributed Antenna System (DAS). The optical transport step of a distributed DAS combines and lowers the power levels for all carriers in the system. This reduces the number of optical links needed, as well as attenuating to a suitable power for existing lasers and optics. Once this composite RF is transported over the optical domain, it needs to be separated and conditioned for insertion into the remote DAS. The DIT system conditions the signals by first amplifying them, and then providing adjustable attenuation to tune the output level.
Remote DIT systems require a separate amplifier circuit for each of the cellular frequency bands in the system. Amplifiers are particularly sensitive to being overdriven in a DAS system. Previous versions of the Optical Zonu DIT trays would need to be returned to the factory in the event of a single amplifier failure. The new “Pluggable DIT” systems provide each separate amplifier in a discrete hot swappable tray. In the event that an amplifier is damaged, the component can be replaced without having to effect the system as a whole.
In typical cellular DAS systems any interruption in service has to be scheduled in advance as a Service Window. The Zonu Connect DIT trays provide service for up to 6 bands for an entire MIMO sector per 1RU tray. In the event of a band failure, this is a large amount of service to bring down for maintenance. In addition to the capacity and service window issues – the DIT trays were also very large as a whole. This would mean shipping back to the Zonu factory would be expensive. The new design allows small amplifier modules to be kept on hand, and replaced in hot swap fashion without having to schedule a service window. Furthermore, shipping back for RMA repair of the damaged card modules has become dramatically less expensive.
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