Research of a frequency band¶

When designing an RF link, one of the first tasks to realise is to define the frequency band that is adapted to the application foreseen. In fact, the frequency spectrum is shared among users in order to regulate RF emissions, and avoid interferences among various equipments.

There are international and national regulation agencies that allocate frequency band to users, with a limited bandwidth and a maximum emission power authorized for the equipment. In France, the ANFR (Agence Nationale des Fréquences) is the agency in charge of the frequency allocation and regulation, and the TNRBF (Tableau National de Répartition des Bandes de Fréquences), describes how the frequency spectrum is shared among services and users.

There are two approaches when researching a suitable frequency band for an application:

• Approach n°1 is the fastest, and consists in searching among “free bands” one that could fit our application, in term of bandwidth and emission power available.
• Approach n°2 requires more time, and consists in searching in the TNRBF an available bandwidth and sending a “request for allocation” to the ANFR.

1. Issue of free frequency band

For the design of radio systems with no license dedicated to data transmission, special authorized frequency bands exists and lead to simple et efficient solution. These bands are précised in the ANNEX 7 of the TNRBF, which specifies the free bands dedicated to low range and power equipment. In particular, the section for non-specific equipment is particularly adapted for TM/TC activities, data and video transmission (c.f. ANNEX I).

Considering the high range required for the link (minimum 50km), there are two suitable bands with different characteristics:

• 868,7-869,2 MHz offers a 500 kHz bandwidth and ERP=25 mW leading to EIRP=41 mW
• 869,4-869,65 MHz offers a 250 kHz bandwidth and ERP=500 mW leading to EIRP=820 mW

With

ERP: effective radiated power (ERP), often used to describe low frequencies systems.
EIRP: effective isotropic radiated power (EIRP), often used to describe high frequencies systems.