Distance issues with RFM69HW



  • Hello. New kid on the block here.

    I am starting to build my sensor network to use with pimatic, based on this framework. I have chosen for the RFM69 on 868 MHz because of my living arragements. I live in an apartment block with 160 units. Most of these have a WiFi router in the 2.4GHz band, so it would be kinda stupid to try and squeeze my sensors in that band with the NRF. My actuators are in the 433MHz band and my current sensors are also based on 433MHz. Sometimes the actuators miss commands because of sensor data floods. Highly annoying.

    Now my problems: I've built my gateway from a Moteino USB R5. Using V1.5, the gateway runs normal, apparently. I get normal messages in the serial monitor.
    The node is built from a clone Pro Mini 3.3V (this one uses a beefy AMS1117 regulator, capable of 1A), a DHT22, and a RFM69HW running at 868MHz. I have already soldered a 4,7µF cap directly on the Vcc and Gnd pins of the radio.

    When the gateway and node are 1 meter apart they communicate perfectly. When the distance grows beyond 2 meters: nothing....

    I have tried different antennae: on the gateway I started with a stub of coax to a SMA connector with a 1/4 rubber antenna. I later changed that to a tuned coil (bought prefab for 868MHz). On the node I started with a piece of wire(delivered with the moteino) later changed to the tuned coil.

    Power to the Moteino: directly from a computer through the on-board regulator(MCP1703; 250mA).
    Power to the node: through FTDI adapter. First the regulator on the FTDI bypassing the AMS1117, later changed to 5V from the FTDI using the AMS on the Pro Mini.

    Browsing the forum I found that people have better results when using the dev-branch. I had hoped to stay away from that.

    What am I doing wrong? Hardware or software?


  • Mod

    @DavidZH said:

    Most of these have a WiFi router in the 2.4GHz band, so it would be kinda stupid to try and squeeze my sensors in that band with the NRF

    Not necessarily. The NRF has many more bands above the WiFi spectrum, that will not interfere with WiFi.
    You could give it a try and see how it works out.



  • You are probably right, but I had already committed to the RFM by buying a Moteino and 4 radio's. Next to that is the lower penetration through concrete. Between the gateway and 2 future sensors is a '70s style bearing wall (25cm thick). I prefer lower frequencies to counter that.

    And thanks to this topic by Carsten I have solved it.
    Why I thought the radio calls in gateway and sensor should not be equal is beyond me...

    I did use the hack of changing the -H version in the MyTransportRFM69.h file to "true" after trying to do that via call from the sensor sketch.

    For now that works. When 1.6 drops I will see I can make it work by calls.
    Now build my other sensors and see if I can make it talk to pimatic!


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