Class License and the ISM band

When you ordered your Moteino you had to make the choice which radio frequency the board will work on. This brings us to a great entry point for this guide. The selection of which frequency depends of where you are in the world and which license you use for transmitting with the radio.

“Hang on.. I need a license?”

Yes, but you may already be licensed.

The good news is, governments in most countries have allocated several areas in the radio spectrum that are free to use as long as your transmitting device falls within certain conditions. 

The correct jargon for such an arrangement is a ‘Class License’.

Take for example Bluetooth or Wi-Fi. You don’t have to sit for an exam or apply for a license when you buy a Bluetooth headset or a wireless network router or access point. The reason is that these wireless radios adhere strictly to the conditions and restrictions of the appropriate Class License and can therefore be bought and used by everyone even without any prior knowledge of radio theory, antennas or what frequency to operate on.

Class License conditions differ slightly from country to country but generally the following aspects are specifically defined:

  • frequency range

  • maximum output power

  • modulation type

  • width of the signal

  • how long it can stay on one frequency

  • what you can use it for

  • contents of what is being transmitted

The Class Licenses that are of particular interest for using a Moteino are the Class Licenses for the ISM bands. ISM stands for Industrial, Scientific and Medical. In the ISM bands you may encounter lots of industrial radio-frequency noise from heaters, machinery, medical imaging devices and all sorts of other bursts of energy that are either too wide-banded or simply do not fit into any other category.

It is in these ISM frequency ranges that low-power transmitters may be operated. Examples of devices other than the Moteino that share these ISM bands are: garage-door openers, Wi-Fi, Bluetooth, cordless phones, mice and keyboards, small radio controlled planes, cars and boats, RFID tags on clothing, telemetry in domestic electricity meters, etc.

Although the ISM band is Licensed and you are granted the permission to transmit in it, you have no additional rights whatsoever. If you happen to fly your expensive remote-controlled drone over a factory and the factory’s rf noise interferes with your drone’s transceiver (transmitter and receiver) and the drone is damaged you have no legal leg to stand on to recover any damages. In other words, the frequency you use is not protected simply because you were there first.

In most cases however, you will find that the ISM bands are relatively quiet simply because there are not that many Industrial, Scientific and Medical radio transmissions going on in domestic areas and the low-power-like Class License transmissions from garage door openers, remote controlled planes, Moteinos, etc.. are all very limited in how much power they may output.

Now you can understand that if you were hoping to use your Moteino in a big production factory you may have very limited success in achieving a reliable radio link.