As we saw many design for this Yagi feed point.

Q1 . Which one would be the best resonator / driven? Gamma match, T-match, delta match, folded dipole, quad, loop?

Q2. And what is the reason if people use such design instead of another design?

My question apply for VHF band. Narrow bandwidth preferred. Design complexity and economical cost are doesn't matter. Highest gain is the main goal.

So far, I've build Super Boomer, Special ZL and T-match. And actually, I don't know which one is better. I only have a home brew RF strength meter here, and it seems they radiate the same strength.

So it's come to my mind that these driven things are big enigma to me.

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    $\begingroup$ Can you make your question more concrete? In particular, specify what you mean by “best”. Highest gain? Loosest tolerance in construction? Easiest to build? $\endgroup$ – Kevin Reid AG6YO Jun 12 '14 at 20:03
  • $\begingroup$ Widest bandwidth? Lowest windload? Lowest cost? $\endgroup$ – Phil Frost - W8II Jun 12 '14 at 20:26
  • $\begingroup$ Aha! In this case is performance, it's gain. Anything else doesn't matter. $\endgroup$ – Bianca Jun 12 '14 at 22:45
  • $\begingroup$ @Bianca Thanks for specifying. Could you edit your question to make this clear? $\endgroup$ – Kevin Reid AG6YO Jun 13 '14 at 3:03
  • $\begingroup$ @KevinReidAG6YO Thank you. I just edited. $\endgroup$ – Bianca Jun 13 '14 at 3:31

If your only concern is maximum gain, then any of the techniques you mention could be considered "best". They are all very good at what they do, they just do it in different ways. If your field strength meter is showing all the antennas producing a similar field strength at a similar distance and input power, then that's proof that they are all equally good, if radiating a strong and efficient field is your goal.

The choice of which techniques to use is largely based on factors other than performance. For example: a delta match can match only resistive loads, whereas a gamma match can also match capacitive loads. But, the gamma match is more difficult and costly to manufacture. The delta match works with a balanced feeder (ladder line), whereas the gamma match works with an unbalanced feeder (coax).

As another example: a simple dipole radiator is easy to manufacture. A folded dipole has four times the impedance of the equivalent dipole. The parasitic elements of a Yagi tend to lower the feedpoint impedance, so increasing it with a folded dipole might be good. But if you already have some other matching technique, then maybe the folded dipole is useless complexity.

  • $\begingroup$ Aha, so it's all about how we would like to load our Rigs, all of those things are all about it ? I saw another driven design, it's called LFA by G0KSC. Will i get a better resonator on this design? $\endgroup$ – Bianca Jul 5 '14 at 10:53
  • $\begingroup$ @Bianca Yes, that's pretty much it: a Yagi tends not to have a 50Ω feedpoint impedance, and these are all ways to transform or alter the feedpoint impedance to look like 50Ω. They all will get the job done well enough. In particular this LFA thing seems to have a lot of unsubstantiated claims. It looks basically like an ordinary Yagi with a folded dipole driven element. $\endgroup$ – Phil Frost - W8II Jul 6 '14 at 21:54

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