Hello,

I just finished building this one:

http://www.drslick.org/Temp1/yagi929.jpg

It's quite unusual, in that there are no directors and two
reflectors.

Here's the H-plane plot (the pattern looking down on the antenna
from above, when the elements are vertical) in the yagi optimizer
program that i used:

http://www.drslick.org/Temp1/yagi929.jpg


It's an interesting method that my friend used to get the
pattern we wanted. We couldn't use the optimization algorithms,
because these are designed to maximize the frontal lobe (can become
quite narrow in span), whereas we wanted something with a 180 degree
pattern.
Notice it's about only about -2dB at 90 and 270 degrees. Also
note that the outer edge of the pattern is about 4.51 dBi, so the dBd
(decibals over a dipole) will be somewhere around +2.4dBd or so.
This isn't that much gain, we realized, but the constraining
factor was to make the yagi as compact as possible, so as to keep the
landlord quiet. So we ended up with 3 elements minimum, in order to
achieve the pattern and get close to 50 ohms.

This antenna was designed for use when you are on the edge of
your city, and you don't wanna waste ERP into the mountains or
whatnot.

As you can see in the Jpeg, it's built with HomeDepot stuff: 2"
pvc and 5/16" treaded stock rod, which comes in lengths of 3 feet,
with nuts used to attach lugs that are soldered to an SO-239, and for
attaching to the PVC itself. Buy the connecting "link" nuts (they are
longer than regular nuts), and you can put these on the ends to tune
the lengths for best SWR.

Here's the basic plans:

Position (inches) 1/4 wavelength
(inch)x two

Driven element: 0 29.4"
Reflector 1: 12" 38.01"
Mast: 48" try for non-resonant
length
Reflector 2: 58" 32"


So you will obviously have to make a two times the 1/4
wavelength that you see, to make a dipole. The DE has a space between
the elements, but the reflector sections can be attached inside the
PVC.

Supposedly, the mast has no effect at a distance of 48" from
the DE, but when i simulated this in the YO, the length of the mast
DID matter, so it's advised that one make the mast at a non-resonant
length, which for 92.9 megs would be avoiding a multiple of 5 feet.

I didn't get a chance to measure the F/B ratio, nor do i really
have the proper equipment to do so, but it's certainly directional, as
a field test has proven.

Questions and comments appreciated.


Dr. Slick

(not a real Doctor)