My, we can sure learn a lot of new things about Yagis from this
newsgroup. Unfortunately, they're not true.

I have a very high confidence in the ability of EZNEC to accurately
model Yagi antennas. This is due to feedback from several professional
customers who have analyzed Yagis with EZNEC and tested the actual
antennas on test ranges.

Let's take the EZNEC example file NBSYagi.EZ.

If you change the driven element (wire 2) length from 2 * 54.875" to 2 *
54.56", you'll find that the feedpoint impedance is 11.53 - j0.0752 ohms
-- it's resonant, and it's certainly functioning as a Yagi. The pattern
and gain are nearly identical to the original NBS design.

Now, change the director (wire 3) length from 2 * 54.313" to 2 * 56".
This drops the gain from 9.68 dBi to 8.66 dBi, and lowers the feedpoint
resistance from 11.53 ohms to 7.849 ohms. The point of maximum gain is
obviously not the point of minimum feedpoint resistance.

Anyone having an explanation for why the gain should be greatest when
the feedpoint resistance is minimum and why a Yagi can't work when
resonant should examine their explanations carefully in order to uncover
the flaws that are obviously present in the explanations.

Roy Lewallen, W7EL

Tom Ring wrote:
Ian White, G3SEK wrote:

Dave Shrader wrote:

If the Yagi is to be tuned for MAXIMUM gain, and that is the
objective, then Ro will be the lowest value at resonance.



That's an interesting assertion. Do you have further evidence for it?



Yes, quite interesting, since a yagi is _not_ resonant in the design
frequency range, otherwise it couldn't work.

Tom
K0TAR