What you need for a 38mmx38mm camera  cover:

• Block of Balsa wood 40mmx40mmx60mm(or any other, but Balsa is easy to shape)
• Sand paper (240)
• Glass fibre fabric
• Epoxy resin, the one for glassing purpose (not any fast curing Epoxy!)
• 2-component silicon rubber RTV/NV, 500g can
• Polyethylene film (Cling wrap)
• a Tetra pak 70mmx70mm,  height minimum 70mm (milk pack)
• Temperature controlled stove (optional)
• Dremel or similar

Read at least once before you start. Don’t hurry, take your time.

1. First you need the Balsa block. A good start is to take measurements on the camera and draw some guide lines on the block. Trim the block roughly in shape with a sharp knife and sand until you have the desired finish.
   
2. For the mold cut the Tetra pak in height to around 100mm. Pour roughly 300-400g silicon rubber in the Tetra pak. The final height of my rubber mold is around 70mm. Do not add hardener before!
   Prepare some tooling to press and hold the Balsa block in position inside the Tetra pak, otherwise it will float on top of the liquid silicon rubber.
   Add hardener to the silicon rubber in the Tetra pak. Be careful: To less and this stuff will never cure, to much and it will cure within seconds while you are still mixing.
   After good mixing press the Balsa block into the mixture and use the prepared tooling to keep it down and in position.
   There should be around 10mm of the block left out of the mixture.
   Don’t touch the mould until the silicone rubber is cured completely.
3. When the silicone rubber is cured, screw a wooden screw in the middle of the Balsa block.
   Carefully peel the block out of the rubber, gently pull on the screw and work the rubber block a bit to free the Balsa.
4. Cut the Tetra pak down to the size of the rubber block. The mold is now ready to use. Remove the screw from the block.
5. For a single camera cover you need a piece of glass fibre fabric in size of around 200mmx200mm. I used a single layer of heavy and dense fabric.
6. Put a big piece of cling wrap on the bench (baking paper works too). On top the piece of glass fiber.
7. Mix a good amount of epoxy resin. I used roughly 8g for a single cover.
8. Soak the piece of glass fibre. Make sure you spread the epoxy equally. Wait some minutes until the glass fiber is soaked completely.
9. Center the piece of glass fibre on top of the mold.
10. Wrap the Balsa block in cling wrap. With the block push the glass fibre gently into the mold. Make sure the glass fibre is spread equally inside the mold.
11. Use a big hobby clamp to keep some gentle pressure on the block. Not to much. The rubber block should not deform.
12. Keep the mold at rest until the epoxy is cured completely. Optional: Use an electrical stove with temperature control and bake the mold. I used 30min at 100°C. Do not apply more than 100°C, better less.
13. When everything is cured you can peel the camera cover out of the mold.
    Put the screw back into the Balsa block. Now work the rubber block a bit and gentle pull the Balsa block together with the cover out of the rubber.
    Now pull the Balsa block out of the cover. The cling wrap keeps sticking. Just peel it off the covers inside.
    
14. Cut the rest of glass fibre from the cover.  Make the hole for the lens (don’t use a drill but a Dremel with grinder).
15. Last, sand the outside of the cover a bit, apply spray filler and paint as desired.

That’s it. You are done.

The cover is a bit fragile. So it’s a good idea to use a piece of plywood to stabilise from inside and also to keep the camera board in place.

Finally after spray filler and some paint:

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€.

Construction details from calculation:

VK5DJ's YAGI CALCULATOR

Yagi design frequency =868,50 MHz
Wavelength =345 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 =4 mm

REFLECTOR
167 mm long at boom position = 30 mm  (IT = 77,5 mm)

RADIATOR
Single dipole 160 mm tip to tip, spaced 69 mm from reflector at boom posn 99 mm (IT = 74,0 mm)
Folded dipole 164 mm tip to tip, spaced 69 mm from reflector at boom posn 99 mm (IT = 76,0 mm)

DIRECTORS
Dir    Length    Spaced    Boom position    IT    Gain    Gain
(no.)    (mm)    (mm)    (mm)        (mm)    (dBd)    (dBi)
1    146    26    125        67,0    3,5    5,6
2    144    62    187        66,0    5,8    7,9
3    142    74    261        65,0    7,3    9,5
4    140    86    348        64,0    8,5    10,7
5    139    97    444        63,5    9,5    11,7

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 474 mm including two overhangs of 30 mm

The beam's estimated 3dB beamwidth is 53 deg

A half wave 4:1 balun uses 0,70 velocity factor coax and is 121 mm long plus leads
FOLDED DIPOLE CONSTRUCTION
Measurements are taken from the inside of bends
Folded dipole length measured tip to tip = 164mm
Total rod length =350mm
Centre of rod=175mm
Distance HI=GF=69mm
Distance HA=GE=87mm
Distance HB=GD=105mm
Distance HC=GC=175mm
Gap at HG=3mm
Bend diameter BI=DF=23mm

If the folded dipole is considered as a flat plane (see ARRL Antenna Handbook) then its resonant
frequency is less than the flat plane algorithm's range of 10:1
The cap between the dipole halfs at the feedpoint is not critical but should be less than 5mm.

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

Feedpoint detail:

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

Material costs <10€.

Feel free to contact me if you have questions about the antenna.

I mostly finished my FPV antenna tracker. The mechanic part and basic control electronic are working fine now.

Read all details on my FPV Equipment Page.

From 800MHz up to 3GHz the VSWR is well below 2.0:1 which means the antenna is very broadband.

See also the Logper page for more details.