DIY LF antenna for Proxmark 3 Easy

It’s not in muscle, just under a bit more skin. It gets less range than my brothers on the same locks by a few mm - Maybe 3-5 on an xAC. I’ve always attributed it to being a bit deeper in the hand, but could be wrong, may just be manufacturing tolerance.


For 1 this is a LF coil and the bracelets are targeting HF chips. I have already tried LF and it is much easier to do. If you look through that thread it has been mentioned it would be easier. Since I am interested in the HF fingernails which work well with my last coil design. I have put my work with the bracelets on the back burner for now, although if I am in the mood to work on it there is plenty of optimization to be done.

1 Like

Nicely done indeed @Compgeek - this is exactly the method that I was trying to explain earlier.

A few notes that might help you - 70v for the easy is way way too high. I’m unsure if it will fry anything on the pm3 BUT the t55 in the xrm does have over voltage protection built in - I hit a wall with this when designing the ProxLF in terms of upping the voltage and chose not to go above 26V for that reason. In terms of making that pm3 perform as best as it can - you want to aim for around what the original antenna voltage is.


Thanks @TomHarkness - any advice for mk2 on how I can bring the voltage down without detuning? Is this something that could be simple to tweak?

Good news is nothing on the board seems to have cooked - back to stock antenna and everything seems fine

In the meantime, this is the result of the 3D printing - I think it came up pretty neat!


Figured it out!

I grabbed out my cheap LCR, wasn’t looking for exact numbers, just wanted to figure out a ballpark.

My inductance was slightly lower for a better tune, and resistance slightly higher, but I didn’t think either would be enough to make a difference… I was wrong… 0.02mH between the two is enough at 125kHz to lower the reactance enough to result in the crazy numbers I was getting. Adding a series resistor was all it needed to tame it back.

I did some bench testing of different values (not soldered, just held in place with clips) and settled on 47R, which brought me down to 26V.

I should have gone lower, because once I soldered it and had a better connection it got back up to just under 30V - for my use that’s good enough though!


I don’t get the crazy range that 70V afforded me, but I get a very usable range for what I need. I can now just slap it on my hand in roughly the right spot and consistently get reads, automatic chipset detection, t55 detects, and trace info!

There are certainly things I’d do different if i were to do this again, but I think that’s the end of this saga for now.

Thanks for playing along everyone, and again @TomHarkness, thanks! If you find yourself in Victoria once this virus is gone, I owe you a drink!


My turn. Will post results when done.


Sending sciencey waves your way


First attempt, voltage wayyyy low optimal frequency super low too.


Be aware the length of the rod significantly effects the inductance of the coil as a whole I believe.


So after taking off like 50 turns with basically no change I broke the rod down to about 25mm. Still no significant change though. I chose to wrap the rod with capton tape to prevent scratches to the enamel on the wire. I have unwound and rewound it differently (new wire) to no success. Still stuck around 4.8v and exactly at 46.88 khz still. I unfortunately don’t have a LCR, which is something that I need to invest in but haven’t yet. I’m wondering if the issue is that I’m using about a foot of coax cable between the proxmark3 and the antenna. I still feel like I should see some kind of change by adding/removing coils but other than .1v changes I’m seeing nothing change. I am no expert in rf anything but I am interested. My ferrite rod is 10mm with 2 flats 180° off from each other, and my wire is 30 awg) Any ideas/recommendations? (Other than getting an LCR, which is already on my list)

1 Like

Voltage is way too low!

Definitely shorten the wire length. With it saying the same voltage at all 3 frequencies, I’m guessing it’s too low for it to detect tuning?

1 Like

Forgive the photo, phone in one hand, 2 probes and an rp-sma connector in the other. If I use 2 hands it’s a 0 ohm short. I couldn’t let it go before bed that the readouts were so consistently bad and unchanging. So if anyone is curious, a shorted plug on the end of your coax pigtail causes the above issues. I feel kinda stupid for letting a quick continuity test slip through my fingers after making the pig tail, but the good news is I get actual changing numbers now, so tomorrow evening I should manage a completed antenna after much fine tuning and beer.


I had a half typed message to tell you to check connectivity :sweat_smile: but I got called away from the computer and forgot :sweat_smile: I feel bad now, caught me out a few times with the clips on the coil where I’d not got the enamel off enough. Glad you solved it! Enjoy the cold one!


Boom. 125.00 kHz, 25.99 V. Gonna make a slick case tomorrow.


Very nice! I love the idea to have it neatly on the coax like that, probe style!


I’m 100% sure it will affect the form of the waves, since it’s actually wrapped around the coax and not round, and I’m sure the flat will have a similar effect, so the plan is to more or less “point” a round edge in the direction of use. I can take some good pics today and took a bunch during the build if people are interested. Just didn’t want to hijack/spam this post with too many photos. I ended up with a 22 ohm resistor in series to bring voltage down. I get about 3-4 mm range read on my NExT while set in HID model. It’s similar to the hacked up xAC antenna I first spliced on it as far as range, but not nearly as picky about angle and reliability. I have access to a couple decent Flukes at work so I will try to get some data today if one can measure capacitance. And btw, being the first decently tuned antenna I’ve made, it’s the 3rd core(both the first and second were too short like your first one was :P), and like 6th time I wrapped one.


Pro tip:

Put image’s in here if you don’t want to spam them, then people like me who would love to see your progress and you do not need to worry about spamming this post with too many photos (not that I think you should anyway, sharing is caring etc)

Like this:



Very cool project indeed !

1 Like

Have you modded the easy for an sma connector, have you just tagged it on or something else?

Mine is a proxmark3 rdv2, and I just got a pigtail on amazon that went from the silly little snap on antenna to an rp-sma connector (since I had a ton of rp-sma connectors when I was making fpv cloverleaf antennas(badly I might add)). I finally got an LCR and will do some testing on my antenna this weekend and finish up what I started then post some pics like leumas95 suggested.