A question about a MOSFET circuit in a transceiver

Hi,

I have a question about the circuit in the picture. It's part of a CW receiver. The Rx_In signal comes from the antenna (low pass filtered) and the output goes to a BPF centered in the receiving frequency and then the signal it's mixed and demodulated. I don't understand the part of the circuit below, I think that the function of the MOSFET is to amplify the signal, but I don't know how it's doing it, maybe I don't know about this biasing circuit.

It's a Switch, not an amplifier..

Ok BigBoss, but I don't understand what it's doing. I simulated with LTSpice supposing that Rx_IN is a pulse signal and I obtained that Vout was a reduced version of Rx_IN. Do you think that this is its purpose?