I want to introduce everyone to Alex, aka IBCrazy. Among the FPV crowd he should be knighted. He has shared his knowledge for practically nothing and done a lot of research into making these antennas and making them as easy as possible to build.
He has instructions for quite a few antenna types that have different characteristics. Cloverleaf, Skew-planar and cross-hair are a few and will probably be my choice for FPV work.
I built this one to improve our wireless coverage here at home, I chose it because it is linearly polarised and directional. We have lots of jungle trees in our garden and I can now enjoy wifi anywhere on the property.
Here is a link to his instructions for the BiQuad that are at RCGroups. His articles also feature at the FPVLab forums.
Keep in mind that adding high gain antennas to wifi equipment is illegal in some countries.
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