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Antipodal focusing is an accepted propagation mode in the MF/HF
frequency SWL and amateur radio communities and many stories abound concerning
very long range reception of relatively weak transmitted signals at high
strength levels. The heterogeneous ionosphere will allow for antipodal focusing
on HF but in practice true antipodal focusing is a rare.
A U.S. Government communications agency
propagation study found that true HF frequency antipodal focusing is indeed rare
and partial propagation path antipodal focusing is a more common mechanism
and occurs most frequently around the Spring and Fall
Equinox when the heterogeneous ionosphere is more uniform.
MF frequency true antipodal focusing is virtually
impossible and partial antipodal focusing a distinct rarity. At MF the
propagation mechanisms mistaken for antipodal focusing are chordal hopping
and ionosphere layer ducting.
73,
Thomas F. Giella, KN4LF Retired Space & Atmospheric Weather Forecaster Plant City, FL, USA Grid Square EL87WX Lat & Long 27 58 33.6397 N 82 09 52.4052 W kn4lf@arrl.net Propagation eGroup: http://lists.contesting.com/mailman/listinfo/propagation
PropNET Beacon Program: http://www.propnet.org KN4LF Daily Solar Space Weather & Geomagnetic Data Archive: http://www.kn4lf.com/kn4lf5.htm KN4LF Amateur & SWL Radio History: http://www.kn4lf.com
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