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Old June 5th 18, 05:53 AM posted to rec.radio.amateur.moderated,rec.radio.amateur.antenna
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Default [IW5EDI] The Grid Yagi


IW5EDI Simone - Ham-Radio

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The Grid Yagi

Posted: 04 Jun 2018 12:03 PM PDT
http://www.iw5edi.com/ham-radio/2724/the-grid-yagi


The Grid Yagi (or Grid Quad) is a high performance yagi antenna that can be
built with readily obtainable inexpensive materials. Described here is a 6
element 2 meter version with a boom length of about 1 wavelength.

The boom is made of 11?2 inch pvc pipe, although any suitable material can
be used, such as steel, aluminum, fiberglass, or wood. The elements are cut
from 2 inch by 4 inch galvanized welded wire fencing, with a wire diameter
of 0.078 inch, which is what #14 steel wire becomes when it is galvanized.



This fencing material and pvc pipe are available in any hardware store. The
driven element and the four directors are all 24 inches by 24 inches. The
reflector is 32 inches by 24 inches. The driven element has an 18 inch slot
in it and is fed at the bottom of the slot. At the other end of the slot is
a shorting wire.



I attached the elements to the boom using 1/8 inch diameter fiberglass
rods. Holes were drilled in the boom, and the rods passed through the holes
and around the wires of the elements, two rods per element. Figure 3 shows
the two fiberglass rods passing through the boom and around the wires of
director D4. Rods were also used to stiffen the driven element where the
feed slot was cut (not shown). The fiberglass rods were obtained locally at
Tap Plastics.

It should be possible to use other stiff materials such as shish-kabob
skewers. The element positions are shown in the Table. The elements can be
glued in place or left unglued for easy disassembly.

Simulations were done using 4nec2, Arie’s version of nec2, available free
at Ray Anderson’s Unofficial NEC Archives.



The antenna was fed with approximately 50 feet of RG-8 type coax with a
measured loss of 1.3 dB through a W2DU type balun [3] with three Amidon
beads, type FB-43- 1020 [4]. Figure 4 shows the simulated and measured SWR.
The SWR measurement was done using a MFJ-259B SWR Analyzer. I could have
adjusted the length of the slot to move the SWR minimum to another place in
the band if I desired.



The simulated gain is 11.9 dBi at 144 MHz, 12.1 dBi at 146 MHz and 12.3 dBi
at 148 MHz.



Article by ross_anderson originally available at
http://home.comcast.net/~ross_anderson

The post The Grid Yagi appeared first on IW5EDI Simone - Ham-Radio.



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