Making the Helix Antenna

Summary

The helix antenna will be what we use to communicate with the balloon during it’s ascent.

Materials

Materials are:-

Item

Quantity

Notes

100mm PVC Pipe

1 metre

A4 Paper

4 pieces

2mm solid Copper wire

3 metres

Aluminum sheet

1mm thick 50x50cm

Thin plywood

5mm sheet of wood

Pipe Diameter reducer

Created from wood, with a 1inch hole in centre for wooden rod

Wooden rod

1.2 metre 1inch

RG-227U cable

15cm

Male RP-SMA connector

1

Copper Sheet

3cm x 6cm

Hot-Glue Gun

1

Lots of glue sticks

Solder

20cm

3mm metal screws

4

Used to fasten ground plane on to plywood

Copper plate

100mm x 100mm x 0.5mm

Fibreglass Kit

Rougly 4 strips, 6cm wide – total area 0.1m^2

4mm metal screws

4

Used to fix wooden reducer to PVC pipe

Telescope Tripod

1

Used Skywatcher 150mm tripod

Screws – 60mm x 1/4 inch

2

Used to mount wooden rod to the tripod.

1/16 bolt and nut

2

Used to attach ground plane to the Antenna tube

Design Parameters

We obtained details on the design from a number of sites. We ultimately arrived at the following dimensions:-

Parameter

Value

Notes

Gain

12.82

Theoretical gain

Wavelength Reflector

33.236mm

Circumference

357.29mm

Equiv diameter of ~113.73mm

Spacing between turns

81.17mm

Length of each turn

366.39mm

Length of wire needed

2931.15mm

Antenna Length

649.39mm

Spray adhesive

1 can

NOTE: some calculators said 106cm diameter was the correct value. I think that there is a lot of margin for error in the Helix antenna…i.e. wide bandwidth, so I’m trying not to get too concerned about getting it ‘exactly’ right.

Below is a picture shows the antenna part way through construction.

Helix Antenna partially constructed

Construction

The constructions is broken into 5 stages. These stages are listed as follows:-

  • Creation of helix coil on former
  • Creation of ground plane
  • Mount for Tripod
  • Attachment of ground plane
  • Electronics
  • Tuning

Creation of Helix coil on former

We needed to mark on the PVC pipe where the copper wire should follow. We did this by getting some A4 paper and drawing diagonal lines. The design parameters above dictated the gradient of the lines and the spacing. Special care was taken to ensure right hand ‘coil’ was created. The four A4 sheets were then very carefully stuck on to the PVC tube.  I then used a hot glue gun to hold the copper wire in place as I wrapped it around the tube. This was quite difficult and I found it best to move myself around the tube as I coiled the copper wire on, rather than trying to move the PVC former. (If I turned the PVC tube around, the wire got harder to coil it).

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