Hairpin match, yagi plans


Hello. I`m building 5 el 20m yagi, and i would like to match it with hairpin. Can anyone pass me a information how to calculate it? Maybe direct feeding will be better? Or gamma match? Can you share your opinions? Maybe someone know where I can find materials about factory beams, dimensions etc to build a copy of mono- multiband yagi.
Thanks for any help, Mike

Allen C. Ward:
There is a great deal of literature on antenna matching in a number of antenna books and a Google search will give a number of leads.  The hairpin match (Orr called it the inducto match) is used with a driven element which is slightly short and uses an inductor (hairpin) to match the feedline to the antenna.  DX Engineering makes hairpin kits DXE-HMS-1P ($30)for two inch booms and DXE-HMS-2P ($25) for 1 1/2 inch booms.  These are simply two small diameter tubes with a sliding shorting bar.  You can down load many manuals for various antennas.  A couple of hours on the web will result in more information than you can digest in days.
Good Luck Allen

Ralph D'Andrea:
Yagimax software has a module to calculate hairpin matches.  It's a little old, but it works.  It can be downloaded free from the "legacy" section of Simtel --  There are more modern tools out there, but it will get you close.

Using a driven element with a direct feed or a hairpin match  is going to require electrically isolating the driven element from the boom.  This might cause you some construction issues and is probably why you don't see the hairpin used more often.  The gamma match doesn't require this, although it has issues of its own.

I prefer the direct connect method.

I have found that moving the reflector in or out along the boom brings the SWR down to pretty near zero.

Some may feel that this might affect the overall resonance or radiation pattern of the antenna. My experience in using this method however tells me it does not seem to make any significant difference in the way the antenna performs.

I have conducted on the air tests using a gamma matching sytem and then again with a direct connection to the director without any matching system in place at all.

My observations found an improvement in the recieved signal when moving the reflector to achieve the lowest SWR reading. I did not observe any recieved signal increase when moving the reflector along the boom to the exact spacing according to the calculations in the antenna's construction plans. In fact, I even observed a slight decrease in the recieved signal when I followed the spacing indicated in the antena construction plans.

Therefore, I had to conclude that the reflector seemed to work better in the "real world" when it was simply adjusted for lowest resonant SWR, and not adjusted for "calculated" boom spacing.

Your results may vary.

Experiment, experiment, experiment.


Charles - KC8VWM


[0] Message Index