To answer your question, I reached out to the engineers at Impinj, a provider of ultrahigh-frequency (UHF) Gen 2 RFID technology. Here is the response I received:
“The signal goes low for 50 percent of the time during a ‘DATA 0’ and 25 percent of the time for a ‘DATA 1.’ The signal is the energy traveling from the reader to the tag. As you know, this is an RF carrier with modulated data. This data is sent in a string of ‘ones’ (1) and ‘zeros’ (0). For a ‘one,’ the RF carrier is only modulated 25 percent of the symbol time which is referenced to the TARI (type A reference interval). For a ‘zero,’ the carrier is modulated 50 percent of the symbol time. The illustration below, taken from page 24 of the EPC spec sheet, shows this pretty clearly.”
—Mark Roberti, Founder and Editor, RFID Journal
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