How to extend read range of 13.56Mhz RFID reader

Hi!
I am using Skyetek's M2 Module for my RFID reader. I want to increase its read range to about 20 cm more or less. I followed the amplifier and attenuator circuits from this website
http://www.eng.tau.ac.il/yash/kw-usenix06/index.html
I am having problems in combining the amplifier and attenuator circuit. I inserted the amplifier between the RFID module and the external antenna. On the other hand the attenuator's input is connected to the external antenna and its output is connected to the oscilloscope so that I could see if there's signal coming out of the attenuator before connecting it to the receive point of the module. But whenever I do this connection and turn on the DC supply of the amplifier and attenuator circuits, the supply of the amplifier becomes shorted.
I don't know why this connection won't work. Please help me, thank you so much in advance.

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