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2.1) 433 MHz and 868 MHz Antenna Design Examples
For most applications, where space constraints exist, a simple Helical Antenna can be used. The Helical Antenna is a simple construction made from wound solid copper wire.
Some technical data for common frequencies:
- Turns = 17, Coil Diam = 5.5mm, Wire Diam = 0.5mm, Coil length = 22mm
- The groundplane stub between last turn and solder stub = 7mm
- Turns = 9, Coil Diam = 5.5mm, Wire Diam = 0.8mm, Coil length = 13mm
- The groundplane stub between last turn and solder stub = 4.5 mm
Here is how to make such a helical Antenna.
The material of the coil can be either solid copper wire or silver plated copper wire. The solid copper wire when pulled strongly gets a nice tension.
To pull the copper wire you start using about two meter of 1mm solid copper wire which is fixed to a sturdy anchor point. Take a piece of wood and wind the other end to the wood. Now start pulling with both hands on the wood side very slowly, until you notice the tension in the copper wire is getting loose - now pull it 30-40% in length with increased speed. This results in a very strong copper wire with a much higher tension, stiffness and perfect straightness with a diameter around 0,5 - 0.8mm.'
Now take a rod like pencil or a drill with 5mm Diameter and wind the wire around the rod as many time as mentioned above in the drawing according to the desired frequency.
Take care to create the groundplane stub on the lower end. It requires you to bend the wire in the axis away from the coil until it makes a small knee. Now add 3mm of wire by bending it 90 degree to the groundplane stub and the Antenna is finished.
Here is another very common example for Helical Antennas