RFM69HC, Antenna and range, troubleshooting?

  • Hi guys,

    I have built a couple of nodes that I'm trying to slowly add to, so wanted to start with just an arduino nano, level converter, 5v to 3v3 power adapter (LM33) and 434meg RFM69HC's that I have.

    I have wired it all up, set one as a serial gateway, and another with mock mysensors, radio's power up and show all ok, but no traffic between them tested using MYSController. Gateway module is powered from my laptop, the remote unit is powered from a 2.1V USB wall wart.

    Ok, lets try changing a few things, so I swap the LM33 for LM3940 LDO regulators that I also have (And I'm powering the regulator via the VIN pin of the Nano, so bypassing the 5V and 3v3 regulators on the nano to ensure thats not part of the problem). Still no traffic.

    Next step, redo the antennas (Using 1/4 length, so 173mm as advised on some sites and down to 164mm), and on playing with the Adafruit RFM69 test sketch, I find that I can get traffic between the two units if the aerials are only 4-5cm apart max. Ok, a start!

    So, tried replacing the stranded wire antennas that I had with same lengths of solid copper wire (Pulled from some cat5a STP cabling), and that has now gotten me up to a range of about 2m (7 feet).

    So it looks like things are travelling between the two, but the range is really bad. I have noticed with the transmitter that if I touch the antenna, then it reaches further, so should I try again with longer antennas on the transmitter unit? 1/2 wave maybe? Seems a little odd, as I would have thought that a 1/4 wave, dead straight vertical antenna would be good enough for a pretty decent range.

    Would there be any improvement if I was to coil the 1/4 wave wire like you find inside consumer 433meg devices? It seems like it would make things worse than having it straight, but I'm not much of an antenna guy, so I'm not sure what to do next. Is cat5a STP cable too thin a diameter to make a reasonable antenna?

    It seems like the RFM is getting enough power, or should I try a larger cap than the current 47uf thats installed on it? Have I gotten an odd version of RFM? I have an HC according to the unit, and most of the stuff I see talks about HCW or HW....

    Where do I go from here? I'm aiming to be able to get these to the point where I can be confident enough to start fitting one inside a wall plate, but at present thats a long way off, I want to get the basics right first, and figure out how far I can get rangewise from these.

  • Hardware Contributor

    @Chester - I would connect my nodes to the serial monitor and watch what happens. Do you recieve the info in your gw but not to the controller?

    Also check out: https://forum.mysensors.org/topic/666/debug-faq-and-how-ask-for-help