Active 125khz tag

Support
1

So I’m well aware that an active tag would not be something you’d want implanted, batteries potentially having trouble inside of you and all that. That being said I’m trying to find a way to significantly increase the read range of a low frequency card or fob without modifying the reader and while still making the card or fob reasonably small. It doesn’t even have to be the original since we can setup a t5577 to cover almost all of the 125k cards I’ve run into.

Anyone got any ideas or a piece of hardware that can push the same signal that a low frequency card would?

2

Assuming you’re talking implant,

I think you’re looking for a proxmark 3 rdv4 or a chameleon

@Pilgrimsmaster, I don’t know much about the chameleon but you have one don’t you?

3

The Chameleon series of devices is HF only unfortunately, and thus unsuitable for @Ima_Wana_Be’s purposes :cry:

4

To answer your question

image
image500×645 31 KB

5

The Keysy has a “long range” mode, but I don’t know how long that is.

6

How much of an increase do you need?

7

It’s less out of need and more curiosity about the potential. I’d heard the term active tag at one point and thought hey I wonder what’s out there.

Let’s say as an example increase the distance from the reader by a factor of 10 from 2cm up to 20cm.

8

125KHz passive tags can be read at distances up to about 30cm or with special equipment (or very large tags) up to about 2m

455Mhz tags have (under ideal circumstances) been read at ranges up to 3km.

9

Okay so, on the NFC side of things, there are such things as booster chips. The idea is that they go between the NFC chip and the antenna and they have an external power source connected to them which is used to boost the chips interaction with the reader. It works very well, but of course the problem is batteries. That said, there have been examples of booster chips connected to a secondary coil. The secondary coil simply inducts power to energize the booster chip. The advantage to this is that this secondary coil does not need to be able to communicate data. Therefore it can be a high Q antenna that is great at power transfer but not great at modulation. Then, the communication coil can be very low Q to be able to maximize data transmission with the help of the booster chip even though it doesn’t induct power very well.

Unfortunately I’ve never seen this type of setup or chip available for a low frequency applications.

10

@amal have you considered using REALLY large coils? I’m thinking, like a 1" wide strip all around someone’s back. :laughing:

11

Like a relay of sorts, amplifying the signal.

But is there something stopping the potential, I mean from a physics point of view?

I get that there’s not much need for it, if a card is meant to be read from a distance then you put the effort into the reader, probably just simpler that way.

1 Like
12

Not to mention that one reader will be used on lots of tags so a $200 cost increase there for significantly increased range will be easier to justify, but if you increase the cost of a 50¢ tag by 20¢ that is going to be a lot harder to sell.

13

No, just the market… smart watches that have NFC payment inside but have small antennas sometimes use them, for example.