I am convinced after building a wifi yagi?

Question

That the yagi is the way to go! Now for my question...I noticed tho that some signals all but disappeared while others doubled. I attribute this to the possibility of their antenae not being in the right position. I am wondering about a yagi made of circular elements and what type of match to use to eliminate the polarization factor.... Also, where might I find a good yagi calculator for my next antenna.

Answer 1

Ok, not quite sure of your level, so forgive the obvious & boring bits in the answer.

The yagi is a directional antenna.  What you gain by having sensitivity in some directions is lack of sensitivity in others. This is directivity. If you make the pattern (beam) wider to get more directions, the directivity goes down again, so you cannot get wide & high directivity.

In some other space, the same applies to polarisation.  If you combine particular polarisations to get high sensitivity to one polarisation, say horizontal, you must have low sensitivity to vertical.

If you like, if polarisation is a vector from the axis of your yagi, say pointing horizontally, the projection of a vertical vector on this is zero.

If you say combine a horizontal yagi & a vertical yagi by adding the signals, the vectors add & you get exactly the same as a 45 degree yagi.  (Except of course you have losses at the join as each looks like a load on the other.)

So no easy way to win on the polarisation, I'm afraid.

If you just want to break even, you can arrange your yagis staggered in the look-direction so you get circular polarisation. That is combine those horizontal & vertical ones with 90 degrees phase-shift. If you arrange it for left-hand circular you are blind to right-hand circular.  You will however get equal gain to all linear polarisations, both horizontal & vertical.  The result being half what you got with either one, but you get both now.

If you want to pay lots of money, one buy units with switches to change the combining to select H, V, LHC, RHCircular.

My guess is that all you want to cmmmunicate with will be a linear polarisation.  MAtch theirs & you will get the best you can get.  Scatterers mess up the polarisation, but I guess you likely need line-of-sight anyway.

By the way, I no this is not a popular view, but I guess the licence that you operate WiFi under likely has a EIRP (effective isotropic radiated power) spec.  That is you must not transmit energy in any direction above a particular figure.  If you have a really directive antenna, then all your energy is going in one direction & in that direction you are likely out of the spec.

There is an old saying like "common abuse should not imply public license." Just because lots of people do it, does not mean it's ok.

Just because no-one dies now, no life-critical systems stop & get publicised or no planes drop from the sky, does not mean that by some fluke combination of events you won't get that 1/1000000 event some time.  In a country of 300,000,000 people, 1/1000,000 events happen every day.

I know, heavy, but think on it anyway.