A participatory athletic event timing system based on backscattering modulation in the UHF band and including wirelessly encoding writable data tags with participant's bib numbers or a calculated derivative thereof for timing participants in a participative athletic event, and attaching the data tags to the participant's bibs for distribution of the bibs and data tags to participants so as to eliminate the need for matching data tags with bibs and maintaining the sequenced order of the matched data tags and bibs. In a preferred embodiment, when participants register for the event, they are assigned an ID number and a bib printed with that number and having attached to the bib one or more data tag encoded in the tags memory the ID number or a calculated derivative thereof. Before the start of the event, the athlete pulls the data tag from the bib and attaches it to their shoe. Antennas suitably designed and adapted for use with the data tags in participative athletic events are used to communicate with the data tags.