Lesson 13 Radio Navigation
The VOR
What does VOR stand for?
VHF Omni-directional range
108.0 to 117.95 MHz
Operational for line of sight only
Accuracy to within +/- 1˚
Morse Code is the only way to ID for sure
Test -….- code is for alerting pilots when maintenance is being done.
The VOR Sure its cool, but how does it work?
It radiates 2 signals
1st one is in all directions (Omni-directional)
2nd one is rotated about a point (Directional)
Airplane receives both signals, looks at the difference between the 2, the result is the radial
360˚ the two signals are in phase
180˚ the two signals are out of phase by ½
270˚ the two signals are out of phase by ¾
The VOR
Course Roughness
Irregularities caused by terrain
West Practice Area
RPM settings may cause fluctuations
The Cone of Confusion
The VOT
VOR Ground Checkpoint
Accuracy of the tests
The VOR High Service Volume
The VOR Low Service Volume
The VOR Terminal Service Volume
The VOR Head
The VOR
OBS Omni-bearing Selector
CDI Course Deviation Indicator
The scale is 10˚ either side, each dot is 2˚
Ambiguity Indicator TO/FROM and OFF or NAV
The VOR
The white flag is the active indication for the ambiguity indicator
DME
Freq Range 962 to 1,213 MHz
Usually co-located with VOR
Usually freq is paired with VOR so that when you select VOR freq you get DME freq automatically.
DME may exist on its own or with another nav aid such as ADF but will have a VOR freq. published for access.
Required by FARs above 24,000 feet
DME
DME comes in three flavors:
VOR/DME
VORTAC
TACAN
DME
DME is an active system
There is a transmitter and receiver on both ends
Airborne unit sends signal to ground unit
Ground unit replies
Airborne unit measures the time it takes
12 microseconds = 1 mile for a radio wave
A pair of pulses is sent out specific to that airborne unit
Max range is 200 NM
Slant range distance compensate 1 mile for every 1000 feet
The Transponder
May be thought of as a microwave transmitter/receiver.
The radar antenna is also a transmitter/receiver
It will overpower the transponder so it cycles on and off 800 times a second with a target 40 miles out
Primary radar – just picks up reflected energy
Secondary radar – picks up transponders reply
The ADF/NDB
The ADF is in the airplane
The NDB is on the ground
Basically an AM radio station designed for navigation use.
If fact you can use AM radio stations for navigation.
NDBs usually operate in the L/MF (low to medium frequency) of 190 to 535 kHz
The ADF/NDB
How about that switch with all the funny abbreviations?
ADF puts the unit in nav mode, uses the loop (gray box) antenna on the bottom of the aircraft
ANT puts the unit in receive mode and switches to the big long antenna that goes from the top of the cabin to the tail.
BFO puts the unit in Beat Frequency Oscillator
The ADF/NDB
ADF interpretation
MH + RB = MB to
MH is given info for fixed card
For moveable cards read the heading at the top
RB is the bearing measured clockwise from the nose of the aircraft
MB is the bearing measured clockwise from North
Moveable card ADF/NDB
The needle points to the magnetic bearing to
To get Relative Bearing use your formula
Figure 1
MH + RB = MB to
330 + RB = 210
RB = 120 (210-330)
Take 360-120 =240 RB to
Moveable card ADF/NDB
To get Relative Bearing use your formula
Figure 2
MH + RB = MB to
315 + RB = 190
RB = 125 (190-315)
Take 360-125 =235 RB to
Fixed Card ADF/NDB
On these, the needle points to the RB to
For MB use your formula
Figure 4 MH of 320
MH + RB = MB to
320 + 225 = 545-360=185
To get the bearing from don’t forget to add 180
GPS
There are 24 satellites in the constellation
They sit at 10,900 miles and orbit in about 12 hours
There are usually 5 that can be “seen” from anywhere on earth
The signals travel at the speed of light 186,000 miles per second
This requires clocks with accuracy in the billionths of a second (1 foot equals 1 billionth of a second)
The receiver calculates a time distance problem to figure range from a minimum of 4 satellites to determine position.
WAAS
RNAV
Stands for Area Navigation
Basically a VOR/DME computer
You tell it a radial and a distance and it fixes a waypoint at that location
Limitations are you have to be in range of a VOR/DME at all times
GPS is replacing this equipment
ILS
Stands for Instrument Landing System
Consists of a Localizer, which provides course guidance and a Glideslope which provides vertical guidance.
Very accurate, to within 25 feet at the threshold
LORAN C
Stands for Long Range Navigation
On its way out, but is dying a hard death
Works on the same principle as GPS only the stations are ground based