Problem With a Yagi

Hi im really hoping someone can help me here.

I purchased a couple of cheap yagi antennas for a project, however the signal level on both of them is really bad.

So i cracked them open to discover (bear in mind i dont know much about wireless antennas), that the driven elements were both on the piss.

So i straightened these out, but the signal still sux.

http://s15.postimage.org/rih2uzodz/IMG_20120526_141356.jpg

As far as i can tell the incoming connector has each wire connected to one of the elements, however there is also this small wire which is about 1 and a bit inches long which has two cores which is connected with one of the wires onto each element as well.

Forgive the bad illustration.
http://s14.postimage.org/40uhhpjkt/image.jpg

Can someone help we sort out whats wrong with the antennas and why they are performing so badly, is something soldered wrong?

 

It's been a long time since I did anything with Yagi's.

I don't see a reflector element on the photograph, is it cropped out?

The small wire you've illustrated looks like a Coaxial Balun, designed to match the impedance of the antenna to the frequency of the transmission whilst keeping the vSWR low.

You'll probably need a good multimeter and a soldering iron/solder to check it out fully, a basic site on Yagi design is here, linked to the Coaxial Balun page http://yagi-uda.com/coaxial_balun.php

 

I would question the signal loss from the balun to the driven element, possible breaks in the cable or bad solder jobs. Also if you don't have a reflector it's not going to do you much good. As a general rule the more directors you have the more gain on the antenna, although gain is actually determined by the overall length of the yagi and not the amount of directors.

Here is another good link to understanding yagi's.

http://www.hamuniverse.com/yagibasics.html