RFM868MHZ + EU Zwave - possibility of interference?



  • I have searched and found this question asked in several places but at least in my search it was never responded.

    I have zwave devices and a mysensors network coexisting in my home. For the mysensors devices I'm using rfm69hw radios at 868MHz.

    If I understand correctly, the EU Zwave devices use 868.4MHz.

    Given that the same RFM69HW radios can be set to operate at 915MHz, I'm wondering if it would be good idea to make the switch? Does somebody with the same setup have experience with issues caused by interference. Of course, even though the radios can be set ot the new frequency by software, the nodes would have to be accessed and opened as the antennas would still need to be adapted, so the whole change would take some work, so I would only do it if there are certain advantages.

    Thanks in advance.


  • Hardware Contributor

    I've no zwave devices so I can't tell, but with the rfm69 driver and settings you should be able to not get any interferences (and they are not talking exactly the same way) so that should work ok.

    Note: 868Mhz is for EU whereas 915Mhz is for USA (see rf regulation for this)


  • Mod

    The payloads of zwave packets are very small, so of course it could make some interference the real question would if the interference can cause problems between the 2 networks.



  • Thanks both, I think it will make sense to continue using the 868MHz frequency.



  • The people that know me well say I'm one of the "need to see to believe" guys.

    Therefore I decided to get my SDR device out and install it on my PC.

    I then looked at the area around the 868MHz frequency. I then launched a fw update on one of my nodes, and waited for some of the zwave nodes to talk to the controller.

    This capture shows how the rfm69 module is talking at the 868MHz (center red band), while a zwave device send some short bursts of data at 868.4MHz.

    alt text

    The two red areas are quite well separated so it doesn't really look like they could interfere. I repeated the test several times and found that some zwave devices seem to be not perfectly tuned to 868.4MHz, and were transmitting at more like 868.35MHz. Even in this case, there are no signs of interference.

    alt text

    I also took the opportunity to take a look at the 915MHz freq. In Spain this band is not free and happens to be reserved for the 4g data cell communication. In my area this band seems to be really clear, so I guess the cellular antennas are not using them. However, it's not an option if you want to follow the regulations.

    alt text


 

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