nav ADF

purpose

station to station radio navigation system

provides bearing to ground station

ground stations are

NDB (non-directional beacons)

advantages

not restricted to line of sight

limitations

• night effect

• coastal effect

• quandrantal error

• p static

night effect

a portion of the transmitted signal acts as a sky wave and bounces off the ionosphere back to Earth

ADF receiver experiences hunting on the needle

when is night effect most pronounced

before/after sunset/sunrise

high frequencies

coastal effect

when the ground wave reaches a coastline and passes from land to water > direction of travel changes

quandrantal error

electromagnetic fields around 4 quadrants of the airframe cause errors

where is quandrantal error minimal

cardinal points (noise, tail, wingtips)

where is quandrantal error maximum

bearings in between

p static/electrical interference

noise interference caused by poor electrical bonding, inefficient static wicks, motors/generators

equipment

antenna

receiver

control head

indicator

antenna location

top or bottom mounted

antenna

loop and sense antenna

modes of operation

ANT, ADF, BFO

ANT Mode

loop antenna disabled, sense antenna receives

ADF mode

loop antenna disabled, ADF tries to point to the station

fixed compass card

relative bearing to the station

moveable card

pointer points to the station and indicates bearing to the station

RMI

top of card is the heading of the aircraft

VOR and ADF combined

sensitivity test

tests ANT and ADF mode

bearing accuracy testing

tests accuracy of bearing indication

frequency

200-1650kHz

loop antenna picks up

electromagnetic signals

sense antenna picks up

electrostatic signals

why is quadrantal error corrected

to compensate for the aircraft’s hard iron effects on the loop antenna

BFO mode

aids in station identification

generates an audio tone at 1000Hz