A single conversion tuner comprises an image reject downconverter and a plurality of tracking RF bandpass filters ahead of the downconverter for providing image rejection. In this way, a replicated database is maintained during a partial communication failure between the primary cluster and the backup cluster. The receivers employ receiving units also having software modules to receive the secure e-mail, to send data about it to the security server, and to receive back from the security server the messageKey for decrypting the secure e-mail. The invention also includes a device for detecting the fluorescence in or on an assay test strip.