Sporadic E propagation

Sporadic E propagation reflects signals off relatively small ionization patches in the lower E region located at altitudes of about 95~120 km (50~75 miles).

The more conventional forms of skywave propagation in the ionosphere's higher F region refract off layers of electrons knocked off of gas atoms and molecules by intense UV light, which are renewed on a regular repeating daily cycle.

[4] Television and FM signals received via sporadic E can be extremely strong and range in strength over a short period from just detectable to overloading.

Shorter-skip (400–800 miles or 640–1,290 kilometres) signals tend to be reflected from more than one part of the sporadic E layer, resulting in multiple images and ghosting, with phase reversal at times.

However, under exceptional circumstances, a highly ionized Es cloud can propagate band I VHF signals down to approximately 350 miles (560 km).

In this case even Es DVB-T reception might be possible if a MUX uses VHF band 3, preferably channel E5, especially if QPSK mode is used, due to its low signal requirements.

For stations located within ±10° of the geomagnetic equator, equatorial E-skip can be expected on most days throughout the year, peaking around midday local time.

Furthermore, ATSC 3.0 could make sporadic E DTV reception easier, due to its usual modulation scheme being more resistant to multipath propagation, as well as impulse noise encountered on those frequencies.