An acknowledge back (ack-back) pager is provided for use in a paging system including a central station which transmits a group of message signals to a group of ack-back pagers which are addressed as a group. The users of the group of addressed ack-back pagers indicate a response to their respective...http://www.google.es/patents/US4891637?utm_source=gb-gplus-sharePatente US4891637 - Acknowledge back pager with apparatus for controlling transmit frequency
Acknowledge back pager with apparatus for controlling transmit frequency
