A liitle OT: suggestion for antenna shielding
there are a few sources relating the pros and cons of using a shield over the loop antenna.
However, some time ago I found an original way to shield a ferrite loop, it was made by PA2OHH Onno for his Navtex (518KHz) receiver: http://home.hetnet.nl/~pa2ohh/07fer.htm
Onno used a flat, multi-wire cable (like those used with hard-disks) to build the shield.
Perhaps one can make a try in an ultra-light or not-so-light receiver :)