There's yet another tradeoff -- bandwidth, of both the pattern and the
impedance. Close spacing, in particular, reduces the range of
frequencies over which the pattern is acceptable ("acceptable" being in
itself subject to compromise) and over which the SWR is acceptable. But
close spaced or not, it's much easier to tweak a design to work
perfectly at a single frequency than make one that will retain some
semblance of that perfection over a wider range of frequencies.

Roy Lewallen, W7EL

Richard Harrison wrote:
Art Unwin wrote:
"But my main question still remains a pointer to a technical article
that discusses the possibility or impossibility of what I have stated."

I don`t get the question, but it seems to me, Art wants to know if
anyone has written of a method to make maximum gain correspond with
maximum front-to-back ratio in a Yagi.

I haven`t seen it. There is a third factor in the compromise, 50-ohm
feedpoint (or some other convenient impedance).

Kraus gives the Yagi-Uda story in "Antennas" There has been much
experimentation and the tradeoffs still exist. Don`t close the patent
office yet. Almost everything can be improved. Art may be implying that
he thinks he has a way to make a better Yagi. I hope so.

The "ARRL Antenna Book" is a good place to see where the art was at the
time of publication. The Antenna Book devotes a chapter to the Yagi, No.
11 in my 19th edition. The directional patterns show a pair of
troublesome sidelobes in addition to the mainlobe. It`s the sidelobes
which are suppressed at the sacrifice of a little gain. Parasitic
arrays are close-spaced for significant excitation. Close-spacing means
close-coupling which lowers the drivepoint impedance. It`s a tradeoff
again because low impedance eventually limits the antenna`s efficiency.

Best regards, Richard Harrison, KB5WZI

Roy
I understand where you are coming from but your points are all based
around a Yagi with standard feeds !. In my past postings over the years
I have pointed out other methods of feeds that not only broaden the
bandwidth
but uses a high impedance, this done by extreme "close" coupling,
in the order of a inch or so upwards to about 12 inches which I also wrote
up
in a patent some years ago just for kicks.
I myself ,choose not to go less than 26 ohms when designing. and tho I can
make them with very high impedance it is not really required as the ham
bands
are quite narrow. Where I really concentrate upon is to move away
from "mutual" coupling ( what ever that means) which is commonly described
with yagi antennas, to "close" coupling designs which is an entirely new
world when
dealing with feed impedances, as Richards post on coupling some months ago
described so much better than I have done.

Regards
Art



"Roy Lewallen" wrote in message
...
There's yet another tradeoff -- bandwidth, of both the pattern and the
impedance. Close spacing, in particular, reduces the range of frequencies
over which the pattern is acceptable ("acceptable" being in itself subject
to compromise) and over which the SWR is acceptable. But close spaced or
not, it's much easier to tweak a design to work perfectly at a single
frequency than make one that will retain some semblance of that perfection
over a wider range of frequencies.

Roy Lewallen, W7EL

Richard Harrison wrote:
Art Unwin wrote:
"But my main question still remains a pointer to a technical article
that discusses the possibility or impossibility of what I have stated."

I don`t get the question, but it seems to me, Art wants to know if
anyone has written of a method to make maximum gain correspond with
maximum front-to-back ratio in a Yagi.
I haven`t seen it. There is a third factor in the compromise, 50-ohm
feedpoint (or some other convenient impedance).

snip.

Best regards, Richard Harrison, KB5WZI

wrote:

bandwidth
but uses a high impedance, this done by extreme "close" coupling,
in the order of a inch or so upwards to about 12 inches which I also wrote
up
in a patent some years ago just for kicks.

You mean like like the K1FO design? Or something else?

tom
K0TAR

I do not know of any designs
by K1FO, can you elaborate?
Art
"Tom Ring" wrote in message
. ..

wrote:

bandwidth
but uses a high impedance, this done by extreme "close" coupling,
in the order of a inch or so upwards to about 12 inches which I also
wrote up
in a patent some years ago just for kicks.

You mean like like the K1FO design? Or something else?

tom
K0TAR

wrote:

I do not know of any designs
by K1FO, can you elaborate?
Art

The number of his antenna designs is quite large, but all the "modern"
ones, 1990 (maybe earlier) and later, use a very close coupled first and
second director. It is a virtual trademark of his designs. I would
suggest googling for K1FO, and look at what's out there.

Or look in the ARRL antenna books.

tom
K0TAR