Dead zone
In shortwave radio usage, the dead zone is the area in which the ground wave no longer reaches the sky wave reflected by the ionosphere . Seen from above, the dead zone represents a circular ring around the short-wave transmitter located in the center.
The size of the dead zone is determined by the range of the ground wave and the jump distance of the sky wave, both of which are frequency-dependent. While the range of the bump is in the order of 100 km, the sky wave skips several 1000 km and thus dominates the extension of the dead zone.
The higher the frequency of a signal, the larger the dead zone. On the one hand, the range of the ground wave is reduced, as the diffraction of the ground wave on the curved earth decreases and the absorption of the earth increases with increasing frequency. On the other hand, higher frequencies penetrate into higher layers of the ionosphere and can only be refracted back to earth at a flat angle of entry , which increases the jump distance.
The dead zone on the 10 meter band (≈ 28 MHz) of the amateur radio service can e.g. B. from approx. 100 km (ground wave) to greater than 2000 km (sky wave) with normal propagation over the F-layer of the ionosphere.