RaZberry antenna hack

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I started to play with Z-Wave at home lately. I found an inexpensive Raspberry Pi Hat for that purpose which is simply called the RaZberry. It’s compatible with all the raspi models so far and it comes with the complete Z-Wave stack and exposes a WebUI + APIs to the user.

The main issue that I encountered was the range of the antenna, I had a lots of problems to reach devices that were few meters away from the controller just separated by a thin wall, and I hadn’t had any other devices working in that frequency range that could mess with it. It caused transient issues like delays in commands or difficulty to reach devices.

What I did is very simple, I just improved the onboard antenna by adding a copper cable of 14 of the Z-Wave wave-lenght.

To do so I first calculated the size of the antenna, according to the Z-Wave specs, in Europe the frequency is 868.42MHz, so the wave-lenght is 300000868420000 = 0.000345622 meters so divided by 4 it gives 86mm.

Itook a thin copper cable of 86mm and soldered on top to SMD capacitor C7 (like on the picture above).

Results are great, I made few tests around the house and I can say that it improved the coverage by at least a factor of 3. I guess that removing completely the on-board antenna would improve it even more but I didn’t wanted to completely kill it in the first time. Now that I’m confident with the setup I’ll simply cut the copper track just after C7.

A picture of the raspi + the Z-Wave hat and the home-made antenna.