RFID 125Khz RDM6300 handmade antenna - need help

Hi guys, i’m not an expert on RF and neither in electronics allthough i’m facinated with.

I have an arduino and already set up the working sketch with RDM6300 Rfid and it’s original antenna (3,1 x 4,4 cm internal measures)

I’m able to read my rfid tokens and identify them. The next is to put the token on my cat’s collar and get it read when the cat’s come in their wooden home.

I built up a handmade antenna made of AWG 24 (0.5 mm) with the following specs :

turns = 24
internal measures = 25,4 x 26,4

The readings of my token are just as the small original antenna, tokens get read at a maximum distance of 2/3 cm but that’s not enough for me …i can’t ask my cat to rub it’s token against the antenna to be able to go in his home!

Can anyone suggest me a solution without having to become an engineer !? :slight_smile:

Should i shape it differently or do i have to make it smaller?
I would like to be able to read the tokens at 10/15 cm distance.

Thanks in advance for any help.

A larger diameter antenna coil with the same inductance (fewer turns) would give you more range, but it is hard to say how much more. There are various formulas on the web for air coil inductors. Here is one randomly chosen example.

Hello Brattain, Do you have a link where i can find a PCB design for 125Khz? Thank you

The coil forms a tank circuit with a capacitor. The resonant frequency of the tank must be correct, meaning sqrt(LC) = 1 / (2 π f), so L has to be = (1 / 2 π f)^2 / C

You need some means of measuring the resonant frequency and tuning the capacitance to match your coil. Calculators and formulae for a coil like this are fairly rough-and-ready and the environment around the coil will affect the inductance too, so its best to measure the resonant frequency and tune that directly in situ.

And yes a larger inductor has a larger range, but a mis-tuned inductor will have a very poor range. The larger the inductor the higher the voltages in the tank circuit, so you may have to uprate components to handle this.