Beer-CanTenna – A ground antenna for 433MHz TX

This antenna was posted in 2012 on FPVLAB, obviously never made it into the blog…solved. 😉

Just in case someone needs a simple and easy to build ground station antenna, usable with any 433MHz TX, here is a solution:

Beer-CanTenna measurement setup:
Return loss at 433MHz:
Inside the can:
On a tripod, extended to ~3m height:

What you need:
1x Beer can, height 170mm, outer diameter 66mm, top opening diameter 52mm
1x Steel welding rod, 500mm length, diameter 1.5mm
1x BNC or SMA panel mount socket with front side nut

How to build:
– First, enjoy the beer, thats a mandatory step. 😉
– Remove the top cover of the can. In a way, that you keep the outer folded ring.
-Drill a hole in the bottom center to insert the BNC/SMA socket.
– Solder the welding rod to the BNC/SMA center contact.
– Measure the length of the rod including the center contact and cut the overall length to 490mm.
– Insert the socket through the bottom hole and fix with the nut.
– Cover the top opening with some non-conductive material. I used some EPS foam.
– That´s all.

I made a extension pipe with a BNC socket on one end and some tripod adapter on the other. This way I can raise the antenna up to 3m on the tripod.
Extention Ext_Socket Ext_Cable
The antenna connects with a 5m BNC cable to the transmitter.

I have tested the antenna during my 11km flight with excellent results.

A fellow pilot uses a second antenna with 433MHz 3DR radio modes to control his APM2.5 plane. He was 3km out already then chickened.

Note, a different size beer can may require a different length of the welding rod.

Solar charger with MPPT – v2

In December 2013 Linear Technology announced a new chip – LT8490. This chip includes a 80V Buck-Boost Lead Acid & Lithium Battery Charging Controller that actively finds true Maximum Power Point in solar applications.

No yet available, that chip looks very promising. It operates with input voltages down to 6V and can boost that to charge batteries with higher voltage. I made already a schematic and board design from the preliminary datasheet that charges a 3S LiPo from a solar panel with up to 5A. A small board size allows usage in model gliders with large wing span to charge the battery in flight.

See my LT8490 page.

433MHz Half-wave dipole for LRS

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

Required parts

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.

Prepare open end and antenna tube

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

Soldered wires

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.

Dipole feedpointDipoleFeedpoint fix

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

Overall length 300mmEach half 150mmReturn loss

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.

Dipole on Easystar wing