Certain aspects involve narrowband signal transport sub-systems for a distributed antenna system (“DAS”). The narrowband signal transport sub-system includes one or more filter banks that are communicatively coupled to a port of a unit in the DAS. The input port can receive a broadband downlink signal that includes multiple carriers. Each filter bank can generate a set of narrowband downlink signals corresponding to a carrier from the broadband downlink signal. Each filter bank can include demodulators and filters. The demodulators can generate respective frequency-shifted downlink signals from the carrier. Each frequency-shifted downlink signal can have a respective frequency shift from the carrier's frequency that is based on a respective bandwidth for the carrier. Each filter can have a passband corresponding to the bandwidth of a narrowband channel associated with the carrier and can generate one of the narrowband downlink signals by filtering a respective one of the frequency-shifted downlink signals.