Airplane scatter - talking through the sky

Airplane scattering (or most often reflection) is observed on VHF through microwaves and, besides back-scattering, yields momentary propagation up to 800 km even in mountainous terrain. The most common back-scatter applications are air-traffic radar, bistatic forward-scatter guided-missile and airplane-detecting [[Bistatic radar|trip-wire radar]], and the US space radar.

It is also a less common propagation mode used by [[Amateur radio operator|radio amateurs]].

== History ==
Airplane scatter itself had been invented in 1930, but HAM usage lagged until the late 80s. The advent of inexpensive [[Software-defined radio|SDR]] based and [[Tracking (commercial airline flight)|distributed real time flight tracking]] enabled precise scheduling, increasing feasibility.

== Radio amateur usage ==

Compared to a single trail of [[Meteor burst communications|meteor scatter]], the time of opening caused by a single airplane is longer - can be from 30 seconds up to a few minutes. Slight asymmetry can sometimes be encountered both in terms of exact timing and the gain of the path.

Range and possible contact length are affected by the size of the plane, flight level and the approximate crossing time of the central part of the straight line between the two communicating stations.

Both the onset and decay of the channel is rapid, so to improve success rate, a short contact procedure is used.

Contact opportunities can be predicted based on the precise flight paths of surrounding planes. There exist software solutions for prediction using local ([[Aviation transponder interrogation modes#Mode_S|Mode S]] and [[Automatic dependent surveillance – broadcast|ADS-B]]) or online sources.

Microwave access using high gain antenna needs to consider precise aiming that takes into account elevation angles as well.

== See also ==
* [[Meteor burst communications]]
* [[Tropospheric scatter]]

== External links ==


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