The frequencies assigned to private networks are in the bands set out in the table below:
| Frequency Band | 29.7 a 41 Semi-duplex and simplex | 68 a 87.5 Semi-duplex and simplex | 148.4 a 174 Semi-duplex and simplex | 440 a 450 Semi-duplex and simplex | 450-470 Semi-duplex and simplex |
|---|---|---|---|---|---|
Space between adjacent channels | 20 kHz | 12.5 kHz | 12.5 kHz | 12.5 kHz | 12.5 kHz |
Maximum frequency deviation (kHz) | ± 4 | ± 2.5 | ± 2.5 | ± 2.5 | ± 2.5 |
TX base station | Higher freq. | Higher freq. | Higher freq. | Lower freq. | Higher freq. |
TX mobile stations | Lower freq. | Lower freq. | Lower freq. | Higher freq. | Lower freq. |
TX/RX distance - semi-duplex (MHz) | 6.180 | ||||
6.580 | 10.525 | 4.6 | 5 | 10 | |
6.680 | |||||
7.180 |
The choice of band to assign the frequencies is based on the following factors:
- Environment
This factor is vital and based, among others, on noise introduced into the radio spectrum (namely man-made noise) caused by human activity, and on the characteristics of propagating electromagnetic waves; to this end urban, semi-urban and rural environments are considered.
The urban environment is considered to include all the countrys cities and surrounding areas, the semi-urban environment encompasses the towns while the rural environment covers villages and unpopulated areas.
- Operation area (service area)
Understood to be the area in which the mobile stations mainly circulate; also considered is the networks local or ambulatory nature.
- Cellular models associated to the bands
The bands are associated to the different cellular models applicable to national territory, barring the Madeira Autonomous Region where only one cell is considered.
From the perspective of frequency reuse, 3 basic types of cellular model are considered, defined for application to the above indicated bands:
Type 1 Elementary cell with 15 km radius, constituting the cellular model associated with the simplex mode of operation in the 440-450 MHz band and applicable only in the coastal zone of the mainland and the Azores Autonomous Region (fig.1);
Type 2 - Cell defined by a radius of approximately 30 km, associated with the semi-duplex mode of operation in the UHF band and with the simplex mode in the VHF/UHF bands (Fig. 2);
Type 3 - Cell defined by a radius of approximately 60 km, associated with the semi-duplex mode of operation solely in VHF bands (Fig. 3).
The reuse model is based on the K=3 factor in order to prevent interference between cells that use the same frequencies.
In specific circumstances, a non-cellular assignment standard covering all territory on the mainland is considered (Type 4).
