The Grid Yagi

 

Figure 1

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, shown in Figure 1.

The boom is made of 1½ 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, and are shown in Figure 2.  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.

 

 

 

Figure 2


 

 

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 [1].  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.

 

 

Figure 3

 

 

 

Elements

Position

REF

0

DE

12 inches

D1

24

D2

38

D3

63

D4

86

 

 

 

 

 

 

Simulations were done using 4nec2, Arie’s version of nec2, available for free download [2].  The program for the simulation can be found at GridYagiD1.htm.

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 [4,5].  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 gains are 11.9 dBi at 144 MHz, 12.1 dBi at 146 MHz and 12.3 dBi at 148 MHz.  The simulated plots can be found at GridYagiD2.htm.

 

 Figure 4

 

Ross Anderson  W1HBQ  ross_anderson@comcast.net       February 15, 2004    July 27, 2006  

 

References and Links

[1] http://www.tapplastics.com/shop/product.php?pid=159

[2] http://home.ict.nl/~arivoors/Home.htm

[3] http://www.w2du.com/r2ch21.pdf

[4] http://www.amidoncorp.com/aai_cost_largerbeads.htm

[5] http://www.thewireman.com/misc.html

 

My homepage “Ross’s Antennas”, with links to my other pages, is http://home.comcast.net/~ross_anderson

 

Keywords:  disc yagi, loop yagi