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

I stand corrected Roy

Roy Lewallen wrote:

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

I should have stated that more clearly. What I meant was, none of the
elements of a yagi are resonant, except perhaps the driven element. My
point was that the elements except the driven one(s) must be above or
below resonance, or the yagi isn't a yagi.

I have also seen a commercial yagi with the driven element longer than
the reflector, so it likely wasn't remotely near resonance. It was also
a very poorly performing commercial yagi, but that's a different matter.

tom
K0TAR

Roy Lewallen wrote:

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

About what I expected. If someone states something truthfull in this
group, no one responds. And it as a group you are all, even Roy,
obviously subject to this. No one bothered to even think about what I
originally said, or try to see the tongue in cheek.

I guess if you can't argue, it's no fun. I don't blame you all for
that, but it is interesting to observe. And sad.

tom
K0TAR

Tom Ring wrote:

I should have stated that more clearly. What I meant was, none of the
elements of a yagi are resonant, except perhaps the driven element. My
point was that the elements except the driven one(s) must be above or
below resonance, or the yagi isn't a yagi.

I have also seen a commercial yagi with the driven element longer than
the reflector, so it likely wasn't remotely near resonance. It was also
a very poorly performing commercial yagi, but that's a different matter.

tom
K0TAR

Roy Lewallen wrote:

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

Tom, K0TAR wrote:
"What I meant was, none of the elements of a yagi are resonant, except
perhaps the driven element."

That`s usually right. The reflector is lengthened and directors are
shortened to conveniently produce phase relations which determine
reinforcement or repression in directions as desired.

However, this is not the only way. Commercial broadcast curtain antenna
arrays use parasitic elements which have the same length as the driven
elements in some instances. Short-circuit stubs repalace drive lines in
the parasitic elements, and these are adjusted for the desired phasing
instead of adjusting element lengths.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

That`s usually right. The reflector is lengthened and directors are
shortened to conveniently produce phase relations which determine
reinforcement or repression in directions as desired.

However, this is not the only way. Commercial broadcast curtain antenna
arrays use parasitic elements which have the same length as the driven
elements in some instances. Short-circuit stubs repalace drive lines in
the parasitic elements, and these are adjusted for the desired phasing
instead of adjusting element lengths.


That's a nice trick. Of course that still means they aren't resonant
since you just displaced the "center" of the element. Seems a good way
for a broadcaster to be able to adjust the pattern if needed after
construction.

I seem to remember an HF wire antenna project that used that method to
go from driven plus reflector to driven plus director to get a
reversible beam. I also remember a set of 5 slopers that were in the
ARRL antenna book or handbook that could be steered.

Oh well, way off topic here now. cul

Tom
K0TAR

Tom, K0TAR wrote:
"Of course that still means thery aren`t resonant aince you just
displaced the "center" of the element."

Kraus describes adjustment of the phase between driven and parasitic
elements on page 320 of his 1950 edition of "Antennas":

"The parasitic element may have a fixed length of 1/2 wavelength, the
tuning being accomplished by inserting a lumped reactance in series with
the antenna at its center point."

In my case, the "lumped reactance" was a tuned stub adjusted to the
desired phase difference between parasitic and driven elements as
indicated by an RCA WM-30A phase monitor.

Best regards, Richard Harrison, KB5WZI

tom wrote,

About what I expected. If someone states something truthfull in this
group, no one responds. And it as a group you are all, even Roy,
obviously subject to this. No one bothered to even think about what I
originally said, or try to see the tongue in cheek.

I guess if you can't argue, it's no fun. I don't blame you all for
that, but it is interesting to observe. And sad.

tom
K0TAR


You can think of it this way, or more probably, you need to
work on your communication skills.
73,
Tom Donaly, KA6RUH