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I have designed 125 kHz RFID reader circuit with which I can read regular card type tags around 4-5 cm and key tag type around 2 cm range. You can see my current circuit and antenna information from image1 and image2 (changed capacitor value for new antenna.)

My purpose is to improve the read range so I can read key type tags from 5-7 cm. I know tag quality is important, too. I decided the make my antenna bigger as you can see in image3, but there is no improvement at all.

My first antenna got around 500uH inductance and my second antenna got around 800uH.

What should I do the for the range improvement? Does bigger inductance and more current mean better range? Is there any big improvement can I in my circuit?

I have checked the net and the Microchip design guide etc., but couldn't find my missing points. My main field is embedded software development so I lack much in this field.

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My first antenna got around 500uH inductance and my second antenna got around 800uH.

That'll mean that you need to retune the resonant circuit with a different value of capacitance to ensure it is still resonant at 125 kHz.

Does bigger inductance and more current mean better range?

Bigger inductance usually means less current and, because you have detuned the resonant circuit it usually means a lot less current.

You need to focus on producing a larger magnetic field and, that can only be achieved by more current in the reader's coil. That means ensuring the primary transmit coil and tuning capacitors are resonant at 125 kHz AND that the driving signal is capable of delivering a higher current into that resonant circuit.

Then, once that is done you have to consider that reading the tag requires things to be exactly the opposite of what you need to do to create more magnetic field. The tag, once powered, only has limited ability to modulate the magnetic field that powers it. So, if that magnetic field is more powerful, then it's harder for the tag to modulate that field and get the reader to recognize this.

Usually this means designing a much more sensitive receiver circuit in your reader. Are you prepared to do this?

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  • \$\begingroup\$ I tuned them actually,(3V3 square wave) with first antenna circuit i got Vpp=17V and second Antenna i got Vpp=21V ( maybe need a bit better tunning). But as you said i need more sensitive circuit. I have understood the idea behind it, thanks to you. \$\endgroup\$
    – U.Sim
    Mar 3, 2022 at 10:23

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