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<p>used to take a <a href="page.php?w=radio_fix">radio fix</a>. These were introduced prior to World War I, and remain in use today.</p>

<p><big>Radio direction finding</big></p>
<p>The first system of radio navigation was the Radio Direction Finder, or RDF.  By tuning in a <a href="page.php?w=radio_station">radio station</a> and then using a <a href="page.php?w=directional_antenna">directional antenna</a>, one could determine the direction to the broadcasting antenna. A second measurement using another station was then taken. Using <a href="page.php?w=triangulation">triangulation</a>,</p><p>
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<a accesskey="3" href="page.php?w=Radio_navigation&amp;p=5">3.Next</a>
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