Newbie needs help understanding coupling loops....
 

I am building my first antenna for the purpose of receiving WWVB (60
khz). The antenna is 1 meter square wound with 6 turns of RG6. I'm
going to be using a FET for the preamp (very high impedance).

Can someone explain to me the concept of a coupling loop. I see
references to it all the time, but no ones explains WHY we should use
one. Why not connect the receiver to the mail loop? What is the
physics behind the coupling loop?

I know this is a very basic question. Thanks to anyone who will take
the time to explain or point me to a good article.

Stephen