Automatic Direction Finding Flashcards
In what plane does a NDB polarise and which band.
The non-directional beacon transmits vertically polarised signals in the upper LF and MF bands, equally in all directions.
Which frequencies do the NDB use?
Most NDB’s use frequencies between 200 Khz and 500 Khz.
NDB type of emission:
For a NDB not used as holding or approach aids, or those which does not have a coverage of less than 50nm, or are not in areas of high beacon density, what is the ICAO recommended carrier wave and type of modulation?
ICAO recommends that NDB’s radiate an uninterrupted carrier and be identified by on/off keying of an amplitude modulated tone (NON A2A)
NDB type of emission:
For a NDB used as holding or approach aids, or those which does have a coverage of less than 50nm, or are in areas of high beacon density, what is the ICAO recommended carrier wave and type of modulation?
ICAO recommends that these NDB’s radiate an uninterrupted carrier and be identified by on/off keying of an unmodulated tone ( NON A1A)
Which type of emission between NON A1A and NON A2A gives better range for a given power output?
NON A1A
ADF errors:
Explain terrain or mountain effect
Mountains or terrain can reflect the signal and can cause multi path reception. The direct transmission from the NDB is received plus one or more indirect reflections resulting errors. Error reduces with altitude.
ADF errors:
Explain coastal refraction
As a radio wave passes from one medium to another its velocity can change and the signal can bend towards the medium with the higher density.
Which has higher attenuation, land or sea?
land, sea has fairly low attenuation
ADF errors:
Explain night effect
During the day, MF sky waves are normally ineffective due to attenuation in the D layer. At night the layer disappears and MF waves are reflected by the E layer. Ground and sky waves mix and phase differences can cause excessive oscillations of the ADF needle and therefore vague and incorrect bearings.
ADF errors:
what are the 4 methods to minimise night effect?
- Selecting lower NDB frequencies
- Selecting stronger NDBs
- Selecting NDBs closer to the aircraft
- Avoid using the ADF at dawn or dusk
ADF errors:
Explain static interference
Large errors can occur in the vicinity of thunderstorms as a result of static discharge, (lighting) the ADF needle may even point to the Cb rather than the NDB. Precipitation (rain) static also affects the bearing accuracy and range as does static build up on the aircraft airframe and consequent discharge.
ADF errors:
Explain station interference
The MF band is congested not only with NDBs but also commercial broadcast stations and errors can occur if two NDBs are on the same, or similar, frequencies.
ADF errors:
Explain quadrantal error
The aircraft’s metal structure act as a good reflector of the incoming radio wave, which tends to bend and align itself with the aircrafts electrical axis, generally lying in the longitudinal axis. These signals will mix with those entering the loop causing erroneous ADF indications.
Signals arriving from the cardinal points( Right angles to the airframe) are unaffected, but those arriving from the quadrantal points ( 45 degrees to the airframe) suffer the maximum effect.
ADF errors:
Antenna effect
Also called loop misalignment, this error results from the antenna being incorrectly aligned. The error being the value of misalignment.
Fill in the blanks:
BFO NDB
A1A NDBs - BFO on for tuning __ for ident
A2A NDBs - BFO __ for tuning, BFO __ for ident
A1A NDBs - BFO on for tuning and ident
A2A NDBs - BFO on for tuning, BFO on for ident
