SPEAR potential interference

Preventing Potential Interference Problems from SPEAR

There are two areas of concern, interference to local services via direct and ionosopheric propagation, and interference at remote locations from ionospherically propagated signals.

Local interference may be avoided by the selection of frequencies for SPEAR which do not conflict with local usage. We are currently undertaking a survey of existing local services to identify potential operating frequencies.

The potential for interference via ionospherically propagated signals is illustrated in the attached plots generated by a ray tracing model. This model takes a typical ionosphere and neglects D-region absorption effects. Note that the resulting signal level scales are relative to an arbitrary value and the plots are intended to illustrate the situation.

Figure 1

Figure 1 illustrates the situation for the heating mode with the reflected energy being confined to the Svalbard area. This demonstrates that it is essential to avoid frequencies already in use on Svlbard and maritime mobile bands.

Figure 2

Figure 2 indicates the situation for the magnetospheric radar mode in which the operating frequency is greater than the ionospheric critical frequency. Here the majority of the transmitted power penetrates and is lost to space. Low angle energy can be reflected from the ionsosphere forming a circle of illumination which is predominantly over the sea although in this example northern Scandinavia is likely to receive some signal. The level of this signal is very low and we are currently carrying out additional modelling in order to estimate the exact signal levels involved. In practice D-region absorption will significantly decrease the level of signals at these frequencies.