Wifi yagi antenna not working

[macross]

So i'm trying to figure out why my homemade yagi antenna does not work. I followed this tutorial exactly but with my antenna there is no difference at all and to add insult to injury a regular 9dbi rubber duck antenna beats my supposedly 16dbi yagi one. The only fault which could be with my build is that i have used regular rubber duck antenna rp-sma connector for my antenna, because not a single store in my area carries a rp-sma pigtail connector... Also i'm a bit confused why did he connect shield and center conductor to the same piece of wire isn't this a short circuit? Or with RF it works different?

[rob77]

in that video he's not making a short - the coax shield goes to one end and the center wire to the other end of that element made of the thick wire.
btw.. the length of that element is critical - few centimeters off and you might be out of the game but anyways... i'm not an RF expert, but that seems to be wrong.. i think you should use some kind of impedance matching between the coax and the yagi element.

[macross]

in that video he's not making a short - the coax shield goes to one end and the center wire to the other end of that element made of the thick wire.
btw.. the length of that element is critical - few centimeters off and you might be out of the game but anyways... i'm not an RF expert, but that seems to be wrong.. i think you should use some kind of impedance matching between the coax and the yagi element.

The original author of that video has posted this message about impedance matching:

k so I am surprised that no one has posted a comment about this before.  Amateur radio works at a lower frequency yes a Yagi for the lower frequency’s needs a balun in order to match the impedance microwave frequency’s do not. As long as you use 50 ohm microwave rated coax you do not need one and using one usually leads to 1dB of power loss.  It is a misconception probably due to the fact that a lot of the antenna designs are copied from antennas used in the lower frequencies. Higher frequency radio is a different discipline if you ever study this at university that is one of the first things you are told.  I once worked on a radar installation upgrade that had an array of 10 Yagi antennas and none of them had a balun.?

[Stonent]

Element size is based on the wavelength of signal.

So when you hear someone say "2 meter band" that means the wave length is in the 2 meter range, and if you're using a full wave antenna, it would be about 2 meters in length.  Sometimes these antennas are coiled and put inside a tube or in the case of Citizens Band (CB) radio in the US which runs in the high 20 MHz band, the wavelength is very long so the base of the antenna mount usually has a coil of wire that takes up the length and you can adjust the exposed part up or down a few centimeters to tune for best performance.

Wifi wavelength is only a few centimeters so all the antenna parts will be around that for a full wave antennal.

There's also 1/2 wave, 1/4 wave etc designs but that starts to get outside my level of understanding.

[PA0PBZ]

The impedance of a folded dipole is ~  300 ohm, so why he did this I don't know.

a Yagi for the lower frequency’s needs a balun in order to match the impedance microwave frequency’s do not.

As if the laws change when the frequency changes.... sure.

There is an easy way to match the driven element to the coax:
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Tha coax shield at the center of the element, the inner core at the 50 ohm point.

[rob77]

There is an easy way to match the driven element to the coax:
_____________________
          | |

Tha coax shield at the center of the element, the inner core at the 50 ohm point.

thanks for that !  i learned something useful today