Improve 134.2kHz PIT tag RFID reader range
LF RFID read range depends on both the strength of the magnetic charge field as well as the reader plus antenna sensitivity when listening.  One of the challenges in LF RFID antenna design is that it is used to both transmit and receive.

The magnetic charge strength is related to the current flow through the loop. The power can be increased with lower resistance antenna wire or shorter length by using fewer turns.  Decreasing the turns will decrease the inductance which also lowers the antenna Q, which may counteract the power gain from the lower resistance.  The antenna will perform best with the correct ratio of inductance to resistance (Q).

FDX transponders use load modulation to send the 10 byte response so the challenge is to find the small changes in antenna voltage caused by the tag within ambient noise. Effective filtering will increase read range.  Try winding the antenna in a figure 8 to form two loops with opposite flows to cancel noise.

A quiet reader power supply is necessary.  If working indoors, turn off switching power supplies, florescent lights and other low frequency noise generators.

Impedance matching isn't effective when using centimeter diameter loops at kilometer wavelengths.