Frequency usage regulations

  • Hi All,

    I'm not sure if this is the right place for the topic, but I thought it's worthwhile to come up with it somewhere.
    I've looked around at MySensors and I have to say that the developers did a great job, it is obvious that they know what they are doing.

    Unfortunately some of the users not so much. There are a lot of beginners who violate the corresponding regulations. Maybe it is not intentional, perhaps they don't even know that there are rules for the so called license-free bands, too.

    For those who haven't heard about these yet:
    I really don't want to be a party killer, but it is not as free as you think. There are both power and duty cycle limitations for each sub-band. You cannot transmit at +20dBm whenever and whatever you want because it is illegal, but most importantly because it can jam your fellow developers' devices in the neighbor or across the street. The licence-free frequencies are common and shared goodies. When you don't respect the regulations, you basically steal others share. Everybody should follow the rules in order the keep the bands usable.
    Regulations in the EU
    CEPT recommendation which is basically the same.

  • @bakcsa

    It's good to come up with this and I fully agree that we should respect the regulations. You explained it well by the 'stealing' analogy.

    I think the links you've inserted are good, but they provide an awfull lot of information which most probably is not all applicable for our mySensors users. Would it be an option to elaborate what the limits are for us in e.g. using the nrf24L01+ antenna's?

    I'm using 3 nrf24L01+PA+LNA SMA Antennas (amplified) as well as approx. 15 small nrf24L01+ modules in my network. I'm wondering am I still acting within the regulations if I use an amplified nrf24L01+ LNA etc. in max power mode (NRF_PA_MAX) using Channel 24?

    I would really appreciate it if you can tell me if I comply with the regulations.



  • @bakcsa Whilst I agree that conforming with regulations is technically and indeed legally correct, I suggest that very few breach the regs due to battery powered requirements and commonly available devices.
    Where I can see potential for problems, particularly in crowded urban catchments, is when desirability for compact nodes demands very small antennae, and if communication becomes unreliable, the first reaction is to increase power output rather than re-examine the antenna choice. Essentially the devices are all 'shouting' at each other to make up for the weak sensitivity of reception due to the compact antenna.
    I prefer using the lowest power possible for battery longevity, and antennae which give good sensitivity, but I do not have difficult paths to negotiate, nor have an urban environment.
    On the other hand, on a remote farm I would have no issues with using a yagi on a distant node aimed at the gateway to overcome communication difficulty, even though the emission is technically in breach of regulations.

  • @boozz
    It is pretty easy to use these docs. Just look up the frequency you use and check what are the limitations.

    In the ECC document (page 9) you can find the followings for 2424MHz:
    Max power: 10 mW e.i.r.p.
    Spectrum access: No requirement

    This means that you can transmit all day if you want (no requirement on spectrum access), however, the tx power may not exceed 10 mW e.i.r.p. nrf24L01's max output power is 0dBm which is 1mW so using this module you probably cannot violate the rules.

    I did not mention it in my first post, but I'm more worried about the 868MHz band.
    Same doc. page 8, row h1.5 868.7-869.2 MHz
    Max power: 25 mW e.r.p.
    Spectrum access: ≤ 0.1% duty cycle or LBT+AFA

    For this band RFM modules like RFM69HW or RFM95HW are often used. The max output power of these devices is 100mW so if you just set the module to the max TX power, you are already way above the limit.

    The trickier part is the 0.1% duty cycle which means your airtime per device cannot be more than 60ms per minute (86,4 seconds per day) unless your device implements LBT and AFA Sometimes this is hard to respect, especially in LoRa mode.

  • Mod

    @bakcsa said in Frequency usage regulations:

    nrf24L01's max output power is 0dBm which is 1mW so using this module you probably cannot violate the rules.

    That's true when the "standard" nrf24l01+ is used. However, the PA+LNA version is quite popular among MySensors users. The PA Gain is 20 dB which yields an output of 100mW which exceeds the allowed 10mW. The high-gain (usually ~3dB) antenna will focus the radiated energy to push even further away from the allowed level.

    I think the LNA (which yields 10dB) is only used when receiving. If that's true, the LNA does not affect the radiated energy.

    As for the duty cycle, I think the behavior of the popular LMIC LoRa library is good. The library will enforce duty cycle, preventing the user from inadvertently abusing the spectrum. Unfortunately, MySensors does not currently have information on the rules (which would be required to enforce them), nor does MySensors have the ability to enforce or even advice/warn users when they exceed the limits. Enforcing would also cause a lot of strange problems with timeouts, since all timeouts would have to be adjusted dynamically.

  • @mfalkvidd LNA=Low Noise Amplifier, essentially a receive pre-amplifier...

  • Mod

    @zboblamont thanks for clarifying

  • Hero Member

    More people should look into LoRa. The receiver sensitivity is so high that the Tx power can be very low. I've read that it can even operate below the noise floor, at which point, Bob's your Uncle.

  • @bakcsa
    Thanks a lot for your explanation and the directions.
    Thumbs up!

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