As if learning to fly wasn’t hard enough..
Plenty more. I’m learning to explain the operation of two of these abbreviations in order to skill a student up enough for them to be able to pass a night rating flight test.
So, the two are NDB and VOR. Non Directional Beacon and Very High Frequency Omni Directional Radio Range. NDB first.
Think of a beacon on the ground sending out identical signals in all directions at a particular frequency. In the aircraft we have an instrument called an ADF, automatic direction finder. This instrument picks up the NDB signals when tuned into the NDB frequency and the needle on the ADF points to the station. Very simple way of navigating your way around anywhere. HOWEVER! Simply tuning into the NDB and following the needle isn’t exactly the
most accurate way to navigate and won’t be good enough to impress a testing officer sitting in the right seat. We want to be able to track to or from a station on a particular heading, ie. in a dead straight line.
- HOW DOES IT WORK?
The airborne equipment, ADF, contains 2 antennae. A loop and a sense. The loop antenna is not dissimilar to a tennis racquet without strings. When we tune into an NDB, the loop antenna will receive the signal, but in order to pick it up completely it needs to be rotated to be at right angles to it, so the signal passes directly through the antenna and causes no interference, an ‘aural null’. If the antenna is in line with the signal, all it hears is interference. The aural null gives the most accurate indication of a signal being received because a minimum signal can be more easily determined than a maximum.
Now for the sense antenna. Consider the aural null, with the signal passing directly through the loop antenna. The signal could be coming FROM one side or the other, this is the sense antennas job, it resolves the 180deg ambiguity and the head of the needle points towards the station. Very hard to explain without a diagram, sorry..
I’m tired. Will talk more about this and the VOR at next update!