Free tool
Wake the tag
A passive tag has no battery. Drag it away from the reader and watch which gives up first: the power reaching the chip, or the reply reaching the reader.
Move the tag
Power at the chip
Reply at the reader
- Chip wakes out to
- Reader hears out to
- Range in free space
Free space is the best case. A real room is usually 30-40% shorter. Change the rest of the assumptions in the range calculator.
How it works
What you’re looking at
The reader sends out a steady wave. A tiny slice of it reaches the tag, and if that slice is above what the chip needs, the chip wakes up. It has nothing to transmit with, so it answers by switching its antenna between two states. The reflection flickers, and the reader listens for the flicker.
Two things can stop a read. Far enough out, the chip doesn’t get enough power to wake. Or it wakes, and its reply is too faint for the reader to pick out. Whichever happens first is your range. A good reader with a sensitive chip usually runs out of power first. A cheap reader usually runs out of hearing first, which is why the reader is in the list.
What it assumes
Free space: no floor, no walls, no stock, nobody in the way, and a tag lined up with the antenna. Real rooms are usually 30-40% shorter.
The rest is fixed so there’s only one thing to play with: 866 MHz, 1 dB of cable from the reader to a 6 dBi circular antenna that loses 3 dB to a flat tag, a half-wave dipole tag, and a tag that reflects a quarter of what reaches it. The power you pick is what the reader puts into the cable. The range calculator lets you change all of it, and the link under the result opens it with your setup.
Where the numbers come from
Chip sensitivities are NXP’s and Impinj’s own figures. Reader sensitivities are Impinj’s datasheet figures for the E710 and E310 reader chips in each mode. The sums are the same ones the range calculator does. The calculator’s notes list each source.