The instrumented range is the maximum range of a radar in which echo signals can be displayed. It is not a measure of the actual range of the radar or its probability of detection. In most cases, the instrumented range is equal to the largest possible scale that can be set on the displays.
An instrumented range is determined by construction based on three conditions:
- The actual maximum range of a radar depends once on the energetic limitation of the detection range and is subject to very many influences considered in the radar equation. An instrumented range should be larger than this energetic range so that all existing echo signals can be displayed.
- On the other hand, the temporal conditions must also fit,
- so that no ambiguities occur which could lead to misinterpretations. Echo signals received outside the pulse period would result in overreaches that are displayed as interference at an incorrect range.
- However, the instrumented range should also be less than or at most equal to the distance corresponding to the receiving time, because otherwise a second transmit pulse would be seen as a full circle on the displays.
The instrumented range should therefore be technically dimensioned somewhat larger than these conditions specify. In addition, other conditions may also act.
For example, in the case of a maritime surface surveillance radar, its maximum range is limited by the curvature of the earth to a so-called radar horizon. Depending on the antenna height of the radar, this corresponds to about 40 NM or about 74 km. More would simply be unnecessary, so all other conditions (transmission power, receiving time) can be adapted to this distance.