14443 power limit at 13.5 MHz?

[purpleanger]

Hello,

I wanna know about 13.56 MHz 14443 transmit power limit.
and also I wanna know relation between distance (between reader and transponder) and reader power.

Thank you

 

[FvM]

There are two aspects ruling the maximum power:
- complying to the ISO 14433 maximum field strength specification. 14443 is dedicated to proximity range.
- keeping general EMC rules applicable in your country, e.g. ETSI EN 302291-1, see the spectrum mask in the attachment

Generally, the relation between transmitter "power" respectively sending coil current and field strength can be calculated by simple magnetostatic formulas (biot-savarts law, Biot) because the dimensions are always small compared to the wavelength.

P.S.: A good application note from NXP

 

[purpleanger]

Thank you for your answer.
I found about transmitted filed strength limit for ISO 14443. That is Hmin = 1.5 A/m
But I wanna know how can i get power degree ( as watt or dBm).

Thank you.

 

[FvM]

Hmax of 7.5 A/m meter is more relevant for maximum power.

If you read my previous post thoroughly, you may have noticed that I placed quotes around "power". That's because power doesn't directly relate to magnetical field strength. The reader "antenna" can be considered as an inductive coupler, that is only radiating a neglectable amount of power. The input power is mainly defined by the coil losses. As said, you have to refer to magnetostatic formulas to find the relation for your design. The linked application note is presenting some of the calculations.

You'll find however higher power involved with ISO 15596 vicinity RFID. Technical solutions are described in respective manufacturer application notes. See also previous threads, e.g. https://www.edaboard.com/threads/202498/

 

[flatulent]

There is another aspect. Along with powering the RFID card, there is the reverse path. As the distance increases, the effects of "load pulling" decline. At one point the load pull signal is lower than the noise on the reader coil from the drive power.