Re: Filters for portable ops
I bought filters from ICE(Industrial Communications Engineers) years ago to use when our club, WB0RMK, would get to gether to operate in the club category of FISTS CW Sprints. I have also used them with success at Field Days. Morgan Systems took over the manufacture and sales when ICE closed up shop (death of owner...if memory serves me right). You can read reviews on eham.
ICE also offered a Broadcast Interferance Filter (http://www.surgestop.com/filter-products/m-402x-.html) which I often use to keep a line-of-sight AM broadcasting station from bulldozing through some of my simpler QRP receivers.