I use a cheap 433MHz transmitter modules often and every time I need to work out what antenna length I should use because I never write it down. This blog post is me writing it down. The length needs to be an harmonic of the wavelength. The wavelength is speed of light divided by the frequency, or 299,792,458 m/s divided by 433,000,000, or 692.361334873 mm for short.
So the acceptable lengths are…
- 692.36 mm
- 346.18 mm
- 173.09 mm
- 86.545 mm
- 43.273 mm
- 21.636 mm
- 10.818 mm
- 5.4091 mm
- 2.7045 mm
- 1.3523 mm
- 0.6761 mm
In reality I normally go for 87 mm, or 43 mm if I am tight for space and don’t need a strong signal. I did once use a 17.3 cm antenna and the coverage was amazing.
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