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I am trying to understand how range of communication between RFID reader and tag is related to frequency and power.

  1. So if I increase frequency, the range will be shorter or larger? why? (I need to understand basic mechanism)

  2. I have an RFID reader. This one is having a range of only 5-10 cm. I want to increase its range to say 1 meter. I understand that if I can increase output power I can transfer energy to larger distance, so I can energize the tag kept at larger distance. So can I increase the range by amplifying the signals and possibly connecting it with a different antenna which can send the signals to a larger distance? If yes how?

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You cannot change the frequency because it has been tuned for specific frequency, not to mention the legalč stuff even if you could. For given frequency (or better said wave length) there is a relation which determine how far the so called 'near field' extends. And only within this near field passive RFID system could possibly work, because it works similar to the transformer /the energy 'taken' from the primary side indicates the presence of the tag in the field/. The antenna near field extends to 'wavelength / (2 * Pi)'

So if you made the frequency higher, you would actually shortened this reactive detection range. Long range systems (10 m or so) works based on the back scattering principle, much like the radar.

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    \$\begingroup\$ Actually, reading near-field RFID tags far beyond the designed range has been demonstrated. Your rule of thumb is not fully applicable as it ignores the pattern of the field influenced by the nature of the antenna/coil used. \$\endgroup\$ – Chris Stratton Feb 5 '13 at 23:35
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  1. Neither. Frequency is just how long the wave is, how long one period takes. Also, the system is set to a specific frequency and both the transmitter as the receiver have to be on that frequency. When you change the frequency of one, it won't work anymore.

  2. You won't get it as far as 1 meter, the module can't handle such a dramatic power increase. You however might use an extern amplifier. Dismount the antenna, implement the amplifier, and use a (new) antenna. I'm sorry, but I do not know what you should use for this.

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If you change the frequency, the system will stop working; it's tuned to a particular frequency.

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  • \$\begingroup\$ That part of the question asks about the basic mechanism (would be better if it said principle or relation), rather than proposes to literally modify an existing device. \$\endgroup\$ – Chris Stratton Feb 5 '13 at 23:37

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