I reached out to Omnikey, but I have not received a response.
I also reached out to Steve Halliday, founder of consulting firm Hitech Aid. Steve was unfamiliar with the Omnikey 5321 specifically, but said certain high-frequency (HF) readers can be configured to reduce the power output, which would limit the read range. You would probably need to experiment with the output controls to achieve the proper distance.
If RFID Journal‘s readers are aware of specific HF models that would enable you to control the power output, please post model numbers for Felipe. Thanks.
—Mark Roberti, Editor, RFID Journal
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