RF12B Antenna length/type

The antenna length for the 3 different frequencies can be calculated like this:

Length(cm) = 7500/freq(Hz)

Antenna size and frequency are inversely proportional.

  • 433 1/4 wave = ~17.3cm
  • 868 1/4 wave = ~8.6cm
  • 915 1/4 wave = ~8.2cm

Jeenode’s come with a whip antenna cut to length. I wonder if a SMA antenna would be better…and how to connect it up to the SMD board….

The chips on the RF12 is made by Silicon Labs. Some interesting app notes can be found here.

Update: found this in a note on the Silicon Labs site:

“The length is inversely proportional to the frequency and may be calculated by: wavelength in cm = 30,000 / frequency in MHz. Thus, for a quarter wavelength,

l (cm) = ΒΌ ( 30,000 / freq (MHz) )

The formula should only be considered as a course measurement however since the length may actually be shorter if the whip is overly thick or wide, has any kind of coating, or is not fed close to the ground. It may also need to be longer if the ground plane is too small.”

Interesting re the coating. I think getting a good antenna situation is going to help with some of the missed packets.

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