The night effect comes from the ionosphere changing its properties when solar radiation drops. During the day the D layer is present and absorbs lower HF signals, limiting how far they can skip. At night the D layer fades away, reducing that absorption, and the main reflecting layer (the F layer) also shifts in height. This change in height and density means skywaves are refracted back to Earth from higher altitudes, increasing the distance over which they can travel and be received. In short, the ionosphere’s height and reflective behavior change with the day–night cycle, enabling longer-range skywave propagation.

Aircraft electrical systems for avionics typically provide 115 VAC at 400 Hz to power motors and components. This high-frequency AC makes the power transformers lighter and the motors simpler and more compact, which is why the ADF antenna drive motor is designed to run from that source. The other options don’t fit the usual avionics power scheme: 28 VDC is used for some DC buses but the ADF drive is an AC motor, 26 VAC isn’t a standard aircraft supply, and 230 VAC isn’t the common avionics standard in this context. So the motor is powered by 115 VAC to match the aircraft’s normal avionics power distribution.

TACAN in transmit-receive mode is designed to give a complete navigation picture: you get range, bearing, and the station’s identification. The range comes from the DME-like two-way exchange—the interrogator and transponder timing provide the distance to the station. The bearing comes from the TACAN’s azimuth information, telling you the direction to the station. The station identification is continuously broadcast so you can confirm which TACAN site you’re tracking. Together, these three data items—distance, direction, and ID—are why this mode provides the full set of TACAN information.

Triple-modular redundancy uses three identical processing paths running in parallel and a majority vote to determine the final output. The idea is that if one path develops a fault and starts producing a wrong result, the other two paths will still agree on the correct result, so the voter selects the correct output and the fault is masked. This setup greatly boosts reliability because you only need two of the three paths to be correct for the system to behave correctly, reducing the impact of a single component failure. To give a sense of the improvement, if each path has reliability R, the chance that the majority output is correct is R^3 + 3R^2(1−R). That yields a substantial increase over a single path, especially when R is already high (for example, with R about 0.99, the overall reliability becomes around 0.9997). However, remember this protection is against a single faulty path; two simultaneous faults can still defeat the majority decision, and the voter itself is an extra component that can fail.