I periodically search the web for good information on using a hairpin match to tune a Yagi antenna. Almost all the articles I can find are vague, stating the same advice to just fiddle with it until you get the SWR looking decent. Or, they're off at the other end of the spectrum, meaning they don't give simple, practical advice. See: http://theleggios.net/wb2hol/projects/rdf/tape_bm.htm
The "hairpin" patch is a length of wire, bent into a U shape, with the ends attached to the driven elements of the Yagi.See:
It's often more complex than it first appears, but the short answer seems to be that the hairpin match adds a shunt inductance.
The question then becomes, how does one alter the geometry of the wire to change this. Does squeezing the wire closer together add or reduce inductance? Or is it more a function of the length of the wire?
If the latter, then it would seem the best approach is to build something similar to the adjustable hairpin match sold by DX Engineering.
