how to boost rfid signal

I have a situation where I am using a RFID module to read a 125KHz tag, but the signal is very weak, so I would like to boost it. But, I am not sure how to do that. The antenna connects to the module (two pins) but since the signal is bi-directional (i.e. the 125KHz driving signal and the tag response signal) I don't think a simple amplifier will do the job. How to address this issue? Thanks!

Most likely the "weak signal" is due to wrong antenna tuning and matching. At first you should know, for which antenna parameters and operation distance the reader module is designed. If the the send signal shall be amplified, this is almost impossible without accessing the output and input pins of the reader chip directly. You probably know, that during receive the reader is sending continuous wave to detect a load modulation by the tag.

Hi FvM. Thanks, yes that has been suggested that I try to modify the frequency (I can do that within +/- limits of 125KHz). The current in the coil is 120 uA - very small. And with attaching a long lead wire (5 meters) between the module and the coil, there is an almost 50% voltage drop (from 5v ptp to 2.5v ptp or so). Also, the recommended coil is 900uH and I am using 950uH - I don't know how much of a difference that can make?

Any other ideas/suggestions very welcome!

Thanks

I won't suggest to tune the operating frequency but to tune the circuit. 5 m cable is more a problem than 5% variation of inductance. Basically you have to lower the coil inductance to achieve 125 kHz resonance again, could be around 700 uH optimum. Or modify the reader circuit. If the manufacturer of the reader module don't supply sufficient information, get the chip manufacturer application schematics.

Hmm.... Well, actually I don't think it is a tuning issue, as the frequency is still exactly 125KHz.... (measure with a scope). It is (in my view) the issue of the drop in voltage and low current (i.e. not enough to actuate the inductor in the tag).

Yes, the frequency is generated from on the reader chip, but the coild forms a resonant circuit with a capacitor that is tuned to 125 kHz. With 5 m cable, you add at least 500 - 600 pF that detunes the circuit. What is your explanation for the "voltage drop"?