You need:

• SMA Pigtail with your desired coax length, the cable I used is RG316
• Plastic antenna tube (found some made by Reely here in Germany, 380mm long)
• Two pieces of wire each 200mm long, I used AWG28
• Hotglue

Mark the center on the antenna tube and use a solder iron to make a small hole in the tube right at the center. Do not cut the tube in half, this will give a better mechanical stability.
Prepare the open end of the SMA pigtail. Keep the feedpoint cap as short as possible.

Solder the two pieces of wire to the coax open end. Be sure the center wire will not touch the outer shielding.

Pull the wires through the antenna tube and the coax open end into the tube hole.
Then apply some good amount of hotglue to strengthen this point.

Cut the antenna tube including the wires inside to an overall length of 300mm. Each half of the tube to 150mm.

On my EZ* I sticked the dipole through the wing. On the lower end, the antenna tube (and only the tube!) was cut and put back together using silicon fuel tube (from nitro engines). This way it’s flexible and will not break in case of ground contact during landing.

A last helix to cover all interesting frequencies for FPV.

Antenna dimensions:

• Design frequency 2450MHz
• 8 turns
• Wavelength 0.23
• Internal diameter 41mm
• Wire diameter 2.5mm
• Coil spacing 28mm
• Reflector diameter 80mm
• Wave Trap size 15.2mmx7.6mm
• Feed point height 5mm (wire center), see pictures

Antenna dimensions:

• Design frequency 5800MHz
• 8 turns
• Wavelength 0.23
• Internal diameter 17-17.5mm
• Wire diameter 1mm
• Coil spacing 11.8mm
• Reflector 40mmx40mm
• Wave Trap size 6.5mmx3.2mm
• Wave Trap spacing from feed point 2mm
• Feed point height 2.5mm (wire center), maintained over 1/4 turn

My internal helix diameter is roughly 80mm with a coil spacing of 55.5mm. Wire diameter is 3.5mm/10mm².
Reflector size is 250mmx250mm. Center support is made from 6mm Balsa, soaked with epoxy resin.
For matching the IBCrazy wave trap method is used. Trap size is 30mmx15mm. See also http://www.rcgroups.com/forums/showthread.php?t=1377791

Tested the following antenna combinations for video downlink:
1. Flight: Skew-Planar-Wheel on video TX+RX
2. Flight: Inverted-V on video TX and Yagi on RX
3. Flight: Inverted-V on video TX and skew-Planar-Wheel on RX
4. Flight: Inverted-V on video TX and Yagi on RX, pointing in other direction

Designed for ground station use, the antenna was made after the following tutorial from IBCrazy:

http://www.rcgroups.com/forums/showthread.php?t=1352583

0.75mm² copper wire was used for the antenna elements, some hot clue to fix everything and a piece of PVC tube to keep the antenna away from any metal parts of the tripod.

Due to fragility of the copper wire a Styrofoam ball will be used as a protection radom.

62mm is used as quarter wavelength.

Angle (green one) between the “eyes” on one S-shaped wire is 78-80°.
The angle (blue one) of quarter wave sections is 100°.

About fine tuning I found the following:
Green angle >90° will lower the resonance frequency while angles <90° will result in a higher resonance frequency.

Measuring results after proper tuning for 1240MHz:

Return Loss & VSWR

The LNA is set to work in the L- and S-band between 900MHz and 1300MHz. Althought it’s possible to configure the LNA for use in 13cm band (2.4Ghz) as well. See Jim’s page for details.

Some pictures and a gain plot:

Gain is ~15dB @ 1200MHz.

The RX antenna was changed to a new one from China for 15€ and free shipping. This antenna performs best for the price. A range test was stopped at 13km due to lost line of sight. But it’s sure 15km+ can be reached as long as you have line of sight to the transmitter.

The antenna is from eBay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280402380910

Receiver is a standard 1200MHz one, only did the SAW filter mod (descripted here) and added a LiPo volatage monitor with 3 LEDs.

Two Wi.232 modules were used to create a datalink. The transmitter module was sending GPS NMEA strings at 9600Baud while the receiver module was mounted on my antenna tracker, where the data was shown.

The modules were set to 15dBm output power. A 1/4 Lambda whip antenna was used on the transmitter while the Yagi was on the receiver.

When I reached a distance of 10km with direct line of sight to the transmitter I stopped the test. Data reception was stable at this point and the Yagi is proofed to work perfectly.

Construction details from calculation:

VK5DJ's YAGI CALCULATOR

Yagi design frequency =1200,00 MHz
Wavelength =250 mm
Parasitic elements fastened to a non-metallic or separated from boom
Folded dipole fully insulated from boom
Director/reflector diam =4 mm
Radiator diam =3,5 mm

REFLECTOR
121 mm long at boom position = 30 mm  (IT = 54,5 mm)

RADIATOR
Single dipole 116 mm tip to tip, spaced 50 mm from reflector at boom posn 80 mm (IT = 52,0 mm)
Folded dipole 118 mm tip to tip, spaced 50 mm from reflector at boom posn 80 mm (IT = 53,0 mm)

DIRECTORS
Dir    Length    Spaced    Boom position    IT    Gain    Gain
(no.)    (mm)    (mm)    (mm)        (mm)    (dBd)    (dBi)
1    103    19    99        45,5    2,8    5,0
2    102    45    144        45,0    5,4    7,6
3    101    54    197        44,5    7,1    9,3
4    99    62    260        43,5    8,4    10,5
5    98    70    330        43,0    9,4    11,6
6    97    75    405        42,5    10,2    12,4

COMMENTS
The abbreviation "IT" means "Insert To", it is the construction distance from the element tip to
the edge of the boom for through boom mounting

Spacings measured centre to centre from previous element
Tolerance for element lengths is +/- 1 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 435 mm including two overhangs of 30 mm

The beam's estimated 3dB beamwidth is 49 deg

A half wave 4:1 balun uses 0,70 velocity factor coax and is 87 mm long plus leads
FOLDED DIPOLE CONSTRUCTION
Measurements are taken from the inside of bends
Folded dipole length measured tip to tip = 118mm
Total rod length =259mm
Centre of rod=129mm
Distance HI=GF=46mm
Distance HA=GE=64mm
Distance HB=GD=82mm
Distance HC=GC=129mm
Gap at HG=3mm
Bend diameter BI=DF=23mm

The required balun is made from RG316 coax cable and calculated with a velocity factor of 0.7.

The dipole is made from 10mm² (diameter 3.5mm)  copper wire .

Feedpoint detail:

And finaly the plot of the VSWR measurment to proof the construction:

This Yagi is also suitable for 2400Mhz where the VSWR is a bit worser but still below 2 which is still accetable.

Material costs <10€.