Got some 433MHz antennas from ReadyMadeRC. Brand seems to be Linx Technologies. From a quick test on the VNA they look promising. Return loss and VSWR looking good at 433MHz. Will see how they behave at range. Download Datasheet
Here is just another way to make a helical antenna. Cheap and easy. Aluminum sheet reflector, cardboard tube and self-adhesive copper tape. Designed and tuned for 1240MHz this helical has 8 turns on a 85mm diameter tube.
Added some eye-candy after flight testing. Performance is excellent. No difference to the wire wound helical I built earlier..
How to make a simple half-wave dipole useful for 433MHz LRS.
- 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
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.
Just finished with my helix antenna, designed for 1240MHz.
Used the helix calculator from http://jcoppens.com/ant/helix/calc.en.php.
Parameters were 1240MHz, 8 turns, 0.23 wavelengths.
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