; to assure this is the case, Flight inspection organizations periodically check critical parameters with properly equipped aircraft to calibrate and certify NDB precision.
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Night effect: radio waves reflected back by the ionosphere can cause signal strength fluctuations 30 to 60 nautical miles (54 to 108 km) from the transmitter, especially just before sunrise and just after sunset (more common on frequencies above 350 kHz)
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Some types of navaids, such as Non-directional beacons and Distance Measuring Equipment, do not operate on these frequencies; in the case of NDBs the Low frequency and Medium frequency bands are used between 190–415 kHz and 510–535 kHz.
Today the tower is used as a Non-directional beacon (NDB) and is often called the "CB" beacon after the morse code letters that it transmits on 245 kHz, with an output power of 2000 watts.