Technical
NDBs typically operate in the frequency range from 190 kHz to 535 kHz (although they are allocated frequencies from 190 to 1750 kHz) and transmit a carrier modulated by either 400 or 1020 Hz. NDBs can also be colocated with DME in a similar installation for the ILS as the outer marker, only in this case, they function as the inner marker. NDB owners are mostly governmental agencies and airport authorities.
Antennas have as part of their makeup a segment that consists of an inductor and a capacitor in series "tuned" to the particular frequency or frequencies assigned to that antenna. The NDB's tuned segment is part of the antenna itself. What is viewed as the Vertical part of the antenna tends to be the supporting pylon for the capacitive element. At low frequencies the antenna itself is capacitive. (functions as the capacitor in the system). There is often a counterpoise (or bottom section of the capacitor) buried in the ground underneath the antenna. The inductive section is the feedline, and the vertical antenna element itself.
Read more about this topic: Non-directional Beacon
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