Theory - Practice - my Quad


The  quad in the qth of Mario, IK7ZCQ



The choice of a beam instead of an other depends on many factors: electric properties (Gain, F/B ecc.), weight, encumbrance, resistence to the wind, appearance ecc.; in a word: IT'S AN ARRANGEMENT! (I forgot price, but I think a beam should be always Home-Made).
So I rejected Log-periodic dipole arrays for Gain/Size ratio, X-Beam and similar for poor information and Delta for mechanical problems; well, yagi or quad?; what to do? The choice was QUAD and you'll understand the reason reading the following page.



I'll not say you that a quad is better than a yagi: I have not enought knowlegde to do that; I'll just say you what I read on some books.

  1. On "More about cubical quad", when somebody asks if the Quad listen better than the Yagi, author answers he is agree; Quad is a quieter antenna not really for its capture area but for the closed loop configuration.

  2. "Quad works better than a Yagi at a low height": that's true! Yagi is an higher Q antenna and has a very high impedance at the element tips so every closed objects will detune it; Quad, on the contrary, is a low Q antenna and has high impedance on the sides, vertical to the ground. But height has the same effect on angle of radiation for the Quad as it does for the 0Yagi, so a low quad will work better than a low Yagi but it will have a low angle of radiation.

  3. "The Quad is less subject to static noise than the Yagi": that's true! For this reason quad were used in the Desert Storm operation.

  4. At last, a two element Quad will perform as a three element Yagi, a 3 quad as a 4 yagi and so on: if you consider a trapped-tri-bander yagi, that's true!





The graph shows the gain for a 2 element Quad

We said a quad is a low Q antenna: that means it will have a wider bandwidth and Gain, F/B Ratio and S.W.R. will be "the same" for a wide band; that is not so important if you work only CW or SSB but if you use both modes that's very important.
When i tried to project a yagi with a PC I understund it was impossible to have good results on wide bands (28 and 21 mhz); with the Quad this problem doesn't exist: I can use my beam on Cw or Ssb with the same performance; I can do quick QSO on all mode without tuning and this is extremely important during a Contest!


The graph shows the Front/Back Ratio in a 2 element Quad


This is consequence of the beam heigth, but, at the same heigth, it's better in the Quad than in the Yagi.
That's why somebody says the Quad open the band at first and close it at last; do you think that's not important?!