433MHz Half-wave dipole for LRS

[Mictronics]

How to make a simple half-wave dipole useful for 433MHz LRS.

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.

[Crash]

How did you come up with 5.9" lengths on each side. I thought it was 2808/frequency, so in this case 2808/433=6.48" each side

[Mictronics]

I cut the length down while monitoring the return loss/VSWR on the spektrum analyzer. The antenna tube has an influence on the required length.

[luzaban]

I cut the length down while monitoring the return loss/VSWR on the spektrum analyzer. The antenna tube has an influence on the required length.

well then the difference is quit big! Do you know the material of your plastic tube ?

[fmkit]

the antenna length also depends on on TX/RX used. When I trim antennas for best RSSI using RFM22B tranceivers antennas about 20% shorter compared to calculated.

[Mictronics]

well then the difference is quit big! Do you know the material of your plastic tube ?

From the flame probe it looks like Polypropylen or Polyethylen.

[J.Knight]

If you didn't use the tubing and just hard mig wire, what would the length be? Is there a calculator?

Would there be a benefit to using two of these on a diversity rx vs. just two sander style antenna's?

[Mictronics]

The length will be different, but can't tell you for know. Need to setup a measurement.

I have a wing setup with two of these dipoles on a diversity RX, so we will see.

[NDw]

I was reading ibcrazies thread yesterday about the inverted vee, and he said if the vee is 90 degrees the radiation pattern is closer to a sphere. If you made the bottom leg of the dipole parallel with the ground and the top leg verticle, would that work?

[Mictronics]

Makes not much sense to me. But you may add three more ground wires and create a monopole over groundplane this way.