Directional coupler detail

[akohlsmith]

Is there any documentation on the directional coupler? It looks like some kind of large ferrite over part of the board, but I can't see any information other than that the PCB has a stripline.

[xaxaxa]

it's a resistive bridge plus a balun, similar to the coupler used here: http://hforsten.com/improved-homemade-vna.html