S.P Radio of Aalborg Denmark made a beautiful little radio the 66TS, I have one, it contains an RF stage and uses AF127 transistors & others. So they fitted it with a DF antenna input for marine navigation use. I don't have that antenna but I have seen photos of it, it consists of two coils crossed at 90 degrees. It looked like they were probably wound inside PVC or fiberglass tubes to weatherproof them for marine use.
There is some very interesting information about radio direction finding and navigation in the introductory part of the service manual for this radio:
http://www.peel.dk/SP/pdf/Sailor%206...20(Manual).pdf