0
\$\begingroup\$

I am currently researching into the security of RFID based access control in relation with jammers. For an experiment, I am trying to build a device that can jam 125 kHz RFID cards from like a meter away. I have found products on the internet that can do so passively up to 1cm of distance.

What kind of antenna/technology would I need to achieve lets say 20cm or 50cm or even 1 meter of distance with such a device? It's just for the experiment which is stationary, so input power is not a problem as it does not have to be portable. I also have the receiver on a fixed position, so a directional antenna for more power can be used.

The problem that I faced is that my understading is that the antenna has to have a length of wavelength / 2, which for 125kHz would be well over 2km, which obviously cannot be built. Am I missing something here?

Thank you for your help

\$\endgroup\$
1

2 Answers 2

1
\$\begingroup\$

The long ferrite rods in old AM radios may be of use in focusing the Magnetic field.

\$\endgroup\$
1
  • \$\begingroup\$ Ok thanks for the info, I have some laying arounds somewhere I'm going to try this \$\endgroup\$
    – scionX
    Commented Mar 15, 2020 at 9:08
0
\$\begingroup\$

at the scales involved the 125 KHz signale are basically magnetic fields, so to disrupt a card from 1m away you need to make a stronger 125KHz magnetic field in the proximity of the card than the card is making (or the same sort of signal level at-least), that's probably going to require large coils and strong currents.

\$\endgroup\$
1
  • \$\begingroup\$ Ok, so it's not actually RF that can be interrupted? \$\endgroup\$
    – scionX
    Commented Mar 15, 2020 at 9:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.