What are these frequencies used for within the drone technology, and why these values?
- 35 MHz
- 433 MHz
- 868 MHz
- 2.4 GHz
- 5.8 GHz
There are only a limited number of frequencies in unlicensed bands which can be used for radio control, and different countries have different licensed bands for different uses.
35MHz is available for RC use in many countries in Europe, but other countries use a whole variety of other frequencies below 100MHz.
868MHz is allowed for "Non-Specific Short Range Devices in Europe" within certain limits.
Finally, both 2.4GHz and 5.8GHz are ISM Bands with worldwide availability.
I found much of this information in the ISM-Band and Short Range Device Regulatory Compliance Overview document from Texas Instruments.
In terms of actual use, different frequencies have different advantages and disadvantages. So in general:
Lower frequencies require a larger antenna and generally have a lower data rate, but require less power and have fewer line of sight issues.
Higher frequencies have more bandwidth available, so you can get more/wider channels and a higher data rate (see the Shannon Hartley theorem) and you can can use smaller antenna, but line of sight starts to become a major issue, and you need more power for the same range.