NFC antenna amplifier/Resonance Circuit project

Satur9 is going to crucify me.

I have hated the fact that my phone case on the pixel 7 impacts NFC functions so much so I got really interested in reading the projects that Satur9 posted.

I don’t have a VNA scanner yet, although it’s on its way. But I am impatient. So reading back on the forums here I saw someone that just grabbed an NFC fob, ripped the old chip out and added a capacitor.

So I did approximately zero math, I didn’t measure resistance inductance or capacitance.

I had a ton of these tags from another project.

I cracked one open and soldered a 22pf capacitor in place of the chip. I then folded the capacitor over and placed it so that the bulge of the capacitor is in a hollow area of my case and the antenna is over where the antenna of the pixel 7 is.

Through sheer luck this works perfectly and I can now read and write through my case.

As always your results may vary and I did everything incorrectly here but had a successful result.

I will keep a running update log and process build on my github:

Once i conclude the project Gerber files will be available for use under the creative commons license


Why? Sure, it’s not up to his standards but it works.


4 topics, years of research, programs written around his field of study, products released due to his knowledge.

Random guy on the Internet: I soldered this random shit together and it works.


You forgot that he’s one of the giants who’s shoulders you’re standing on. And you’re also being humble about this.

Or at least I think that you made a cool and useful project that might help other people.

Anyways, I have to get back to my lab and pet my oscilloscopes like a normal person… :robot_windows:


make sure to put some cushion around that capacitor, I did this and after a few weeks the capacitor was crushed :confused:

Maybe next version could use a SMD capacitor.

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Here. I didn’t think of using an antenna from a fob though :grimacing:
I later opened up the back lid and put it inside


If I had the smd capacitors laying around I would of. It’s just what I had on hand

This inspired me to whip out my soldering iron and attempt my shot at it. The LED shines brighter it seems like, but my phone won’t read the xSIID at all, just see the normal read cycle. I’ll check it up to a successful task in the form of knocking the rust off my soldering skills onto the antenna XD

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It may be that your right tail on the capacitor is not isolated to the single antenna wire. When I folded my cap over I put some paper over the coil just in case some of the enamel coating is weak and it interferes.

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It is isolated, just a bad angle looking at it.
I will try the paper though!

Also an odd thing, I get reads from the capacitor not the coil

I need this on my front door keypad so I don’t stand out in the heat for 5 minutes contorting my hand trying to get it to read only to eventually be defeated and just put the number code in.

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There are a few examples

Haha, and mine looks the shittiest


Oh thanks for this! I was literally just thinking of posting a thread asking about the possibilities of an NFC repeater or ‘booster’ since my phone as absolutely terrible NFC performance (on a good day I might be able to read my Apex Flex one out of every 10 tries).

This looks like an easy and cheap enough hack that even if it fails miserably I won’t care all that much.

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I’m already so ready for this post

begins reading

I mean you fuckin nailed it. Looks like the Capacitance of the chip you removed was 23.5pF so it’s perfect.

If anybody else is trying to make one and doesn’t know which capacitor to use, you can figure out the correct inductance using that calculator I made, or one you find online.

Once you have an idea of the inductance, you can figure out which capacitor to add to make it resonate at 13.56MHz using this.

Sorry I didn’t deliver on the crucifixion. Fuck up better next time and I’ll be back.


Do they increase scanning range?

I guess you could describe it that way, for some types of transponders anyway. Particularly the small implantable kind. I don’t think you would get any difference in range if you were talking about a full size card, in fact you might get slightly less range with a full size card. It’s more of a magnetic field concentrator then booster or extender.

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I suppose the same principle applies to LF? Approximately what value should the capacitor be for let’s say one of those cheap EM4100 keyfob antenna? I don’t have a LCR meter :pensive:

That gives me ideas :thinking:
I have a load f old mifare cards …

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