A 10 foot yagi design that delivers an impressive 16dbi gain at 440mhz. Fits perfectly into a 10′ PVC pipe that you can buy dirt cheap at any building supply store.

Recipe:

$3.00: 1 10′ PVC pipe, 1″ diameter for best support.
$7.00: 7 aluminum welding rods, 1/16″ x 36″ Go to a welding supply shop they sell them by the lb.
$2.00: SO-239 Connector
$1.00: Silicone sealant in a tube
$1.00: Hot glue stick
$2.00: Paint
$0.10: A scrap of coax for your balun

$16.10 or so for mine.

Construction:

Measure out all elements very very carefully down to the mm according to the plan below. I used a chalk line to then make a straight line down the middle and followed up by drilling the element holes. Use the tightest fit you can manage, use the right size bit for your elements. The best way to do this is to use a drill with a level bubble on the top so you can make sure all your elements are in line. You can always re-drill if you get any odd ones though.

Cut each element very carefully to the exact length, and feed them through. You should use some sort of box or brick to keep it suspended above ground to avoid bending the fragile aluminum elements.

Once the elements measure up evenly (same amount of aluminum rod sticking out each side) fix them in place with a generous dollop of hot glue, all around and out across the rods to get a good surface area binding. Or use silicone if you want to wait.

The folded dipole requires a little special attention to bend it around and get it just right. An ASCII illustration is included. On my antenna I aligned the center of the oval with the elements so that it looks symmetrical and that seems to be the way most builders make them also.

You’ll also need to make a balun to get the impedance down to 50 ohms. I simply used a scrap of coax that I strapped to the antenna. Here is a good website to tell you about making one for yourself: http://www.n-lemma.com/calcs/dipole/balun.htm

The software used to calculate this is described in the following output that I have modified to include a little extra info, and can be freely downloaded from many places online. Google is your friend on that.

Strapped it to my mast and I’m hitting far away repeaters that I never even could hear before. Highly recommended and a nice cheap weekend project.

VK5DJ's YAGI CALCULATOR

Yagi design frequency =444.00 MHz
Wavelength =675 mm
Elements using a non-metallic or separated boom
Director/reflector diam =2.50 mm
Radiator diam =2.50 mm

ELEMENT LENGTHS AND SPACING
Reflector
330 mm long at boom position = 30 mm

Radiator
Single dipole 319 mm tip to tip at boom posn =165 mm
Folded dipole 325 mm tip to tip at boom posn =165 mm

Dir	Length	Spaced	Boom position	Gain	Gain
(no.)	( mm )	( mm )	( mm )		(dBd)	(dBi)
1	300	51	216		5.3	7.4
2	297	122	337		6.8	8.9
3	294	145	482		8.0	10.2
4	291	169	651		9.0	11.2
5	289	189	840		9.9	12.0
6	287	203	1043		10.6	12.8
7	285	213	1256		11.3	13.4
8	283	223	1478		11.8	14.0
9	281	233	1711		12.3	14.5
10	279	243	1954		12.8	14.9
11	278	253	2208		13.2	15.3
12	276	260	2467		13.5	15.7
13	275	263	2731		13.9	16.0
14	274	267	2998		14.2	16.4

Director spacings are measured from the previous element
Tolerance for element lengths is +/- 2 mm

Boom position is the mounting point for each element as measured
from the rear of the boom and includes the 30 mm overhang.The total boom length is 3028 mm including two overhangs  (9.93ft)

The beam's estimated 3dB beamwidth is 31 deg

A half wave 4:1 balun uses 0.80 velocity factor RG-8 (foam PE)  and is 270 mm long plus leads
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A half wave 4:1 balun uses 0.66 velocity factor RG-8U (foam PE)  and is 223 mm long plus leads

Here are some construction details for a folded dipole

Measurements are taken from the inside of bends
Folded dipole length measured tip to tip = 325mm
Total rod length =669mm
Centre of rod=335mm		   FOLDED DIPOLE
Distance HI=GF=145mm		B========C========D
Distance HA=GE=165mm	       A(		   )E
Distance HB=GD=185mm		I=======H G=======F
Distance HC=GC=335mm                   (gap)         
Gap at HG=10mm
Bend diameter BI=DF=25mm

If the dipole is considered as a flat plane (see ARRL Antenna Handbook) then its resonant frequency is 427.9MHz and K is 0.929