1. Parvathavadhani & Srikar 3rd Sep, 2011
Avionics unit 4
Parvathavadhani & Srikar
3rd Sep, 2011
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2. Syllabus VHF Omnirange VOR receiver principles
DME distance measuring equipment, Principles of operations
Instrument landing system
Localizer and Glideslope
Give a brief overview of the presentation. Describe the major focus of the presentation and why it is important.
Introduce each of the major topics.
To provide a road map for the audience, you can repeat this Overview slide throughout the presentation, highlighting the particular topic you will discuss next.

3. Syllabus VHF Omnirange VOR receiver principles
DME distance measuring equipment, Principles of operations
Instrument landing system
Localizer and Glideslope
Give a brief overview of the presentation. Describe the major focus of the presentation and why it is important.
Introduce each of the major topics.
To provide a road map for the audience, you can repeat this Overview slide throughout the presentation, highlighting the particular topic you will discuss next.

4. VHF Omni-directional Range (VOR)

5. Introduction
VOR, short for VHF Omni-directional Range, is a type of radio navigation system for aircraft.
VOR provide MAGNETIC BEARING information to and from the station.
“Omni-” means all and an Omni-directional range means VOR station transmits signal in all directions.
VOR function as marking for the BEGINNING, CENTER-LINE and the END of airways.
In short word, VOR guide an aircraft from point A to point B, from point B to point C.
VHF omnirange (VOR)
Do not be confused by its name, VOR stations provide bearing information relative to the aircraft position.
VOR stations operate in the MHz band with a channel spacing of 50 kHz or 100kHz.
Each station transmits its identification via a Morse code modulated tone.
A reference 30 Hz signal is FM modulated onto the carrier.
A secondary signal is sent by a directed (cardioid) antenna that spins at 30 rev/sec.

6. VOR antenna at vertical
VOR Equipment
VOR antenna at vertical
tail of aircraft
VOR aircraft equipment
-VOR antenna at
vertical tail of aircraft
-VOR receiver & indicator
inside cockpit
Marking the BEGINNING, the END and CENTER-LINE of airways. In short word, VOR guide an aircraft from point A to point B.
As a let-down aid at airport based on procedures.
As a holding point for aircraft
As a source of en-route navigational position lines.
For low-speed a/c the antenna is whip type fitted on the fuselage.
For high-speed aircraft it is a blade type on vertical tail.
VOR Ground Station (antenna)

7. VOR station for broadcast the signal
VOR Ground Antenna
Stationary Antennas
Rotating Antennas
The VOR ground station is oriented to magnetic north.
Consists of :
Single Stationary Antenna at the centre
Rotating antennas
It produces 360° radials/tracks at 1° spacing.
These 360 bearings are known as RADIALS
VOR ground installations are strategically located along air routes and airport to ensure continuity of guidance.
VOR station for broadcast the signal

8. VOR ground antenna
The VOR ground antenna is oriented to magnetic north.
Consists of :
Single Stationary Antenna at the centre
Rotating antennas
It produces 360° radials/tracks at 1° spacing.
These 360 bearings are known as RADIALS
VOR ground installations are strategically located along air routes and airport to ensure continuity of guidance.

9. RADIALS 360 Magnetic North 045 315 135º 270 090 135 225 180
VOR receiver gives 1 LOP called a Radial
135
225
180

10. PRINCIPLE OPERATION OF VOR
How VOR works
The basic principle of operation of the VOR is very simple:
The VOR facility transmits two signals at the same time. One signal is constant in all directions, while the other is rotated about the station.
The airborne equipment receives both signals, looks (electronically) at the difference between the two signals, and interprets the result as a radial from the station.
VORs operate within the to MHz frequency band and have a power output necessary to provide coverage within their assigned operational service volume.
They are subject to line-of-sight restrictions, and the range varies proportionally to the altitude of the receiving equipment.
The VOR system uses the phase relationship between a reference-phase and a rotating-phase signal to encode direction.
The carrier signal is omni-directional and contains the amplitude modulated (AM) station Morse code or voice identifier.
The reference 30 Hz signal is frequency modulated (FM) on a 9960 Hz sub-carrier.
A second, amplitude modulated (AM) 30 Hz signal is derived from the rotation of a directional antenna array 30 times a second.
Although older antennas were mechanically rotated, current installations are scanned electronically to achieve the same result with no moving parts.
When the signal is received in the aircraft, the FM signal is decoded from the sub carrier and the frequency extracted.
The two 30 Hz signals are then compared to determine the phase angle between them.
The phase angle is equal to the direction from the station to the airplane, in degrees from local magnetic north, and is called the "radial."

11. How VOR works
VOR receiver in the cockpit is tuning to the specific frequencies assigned for that VOR ‘s airport.
It is VHF frequency which is between MHz.
The VOR station on the ground transmits two signals at the same time; one signal is constant in all directions, while the other signal is rotated about a point. The VOR on-board equipment receives both signals, looks electronically at the phase difference between the two signals, and interprets the result as the radial from the station. The ground station is calibrated in a way that the two signals are “in phase” (match each other) towards magnetic north on the position where this station is located. So, the required radial from the ground station is in fact the phase difference in degrees between the two signals transmitted from the ground station.
The operation of the VOR on-board equipment starts with the tuning of the desired frequency.
After entering the frequency, the volume control should be turned up in order to confirm that the three letter identification code (Morse Code) is correct.
Identification process is very important and the VOR information received can not be trusted unless the ground station has been positively identified.
Stationary antenna transmits constant signal in all directions and contains VOR station's identifier information given in MORSE CODE.
For example, KLIA airport has a VOR known as VKL-Victor Kilo Lima

12. How VOR works
After entering the frequency, the volume control should be turned up in order to confirm that the three letter identification code (Morse Code) is correct.
For example, KLIA airport has a VOR known as VKL-Victor Kilo Lima
The VOR station on the ground transmits two signals at the same time; one signal is constant in all directions, while the other signal is rotated about a point. The VOR on-board equipment receives both signals, looks electronically at the phase difference between the two signals, and interprets the result as the radial from the station. The ground station is calibrated in a way that the two signals are “in phase” (match each other) towards magnetic north on the position where this station is located. So, the required radial from the ground station is in fact the phase difference in degrees between the two signals transmitted from the ground station.
The operation of the VOR on-board equipment starts with the tuning of the desired frequency.
After entering the frequency, the volume control should be turned up in order to confirm that the three letter identification code (Morse Code) is correct.
Identification process is very important and the VOR information received can not be trusted unless the ground station has been positively identified.
Stationary antenna transmits constant signal in all directions and contains VOR station's identifier information given in MORSE CODE.
For example, KLIA airport has a VOR known as VKL-Victor Kilo Lima

13. How VOR works
The VOR station on the ground transmits two signals at the same time; one signal is constant in all directions, while the other signal is rotated about a point.
One from stationary antenna, while the other from rotating antenna.
The VOR station on the ground transmits two signals at the same time; one signal is constant in all directions, while the other signal is rotated about a point. The VOR on-board equipment receives both signals, looks electronically at the phase difference between the two signals, and interprets the result as the radial from the station. The ground station is calibrated in a way that the two signals are “in phase” (match each other) towards magnetic north on the position where this station is located. So, the required radial from the ground station is in fact the phase difference in degrees between the two signals transmitted from the ground station.
The operation of the VOR on-board equipment starts with the tuning of the desired frequency.
After entering the frequency, the volume control should be turned up in order to confirm that the three letter identification code (Morse Code) is correct.
Identification process is very important and the VOR information received can not be trusted unless the ground station has been positively identified.
Stationary antenna transmits constant signal in all directions and contains VOR station's identifier information given in MORSE CODE.
For example, KLIA airport has a VOR known as VKL-Victor Kilo Lima

14. How VOR works
When aircraft receives these two signals, an aircraft VOR receiver electronically measures the phase angle different between these two signals.
This phase angle different is translated as the MAGNETIC BEARING which tell the pilot the aircraft angle direction to the VOR station.
This bearing angle also known as RADIALS.

17. VOR indicator Omnibearing Selector (OBS).
Allows pilot to select desired course/radial to fly
Course deviation indicator (CDI).
The needle centers when the aircraft is on the selected radial.
TO/FROM indicator.
Shows whether the selected course will take the aircraft TO or FROM the station.
Flags:
The device that indicates a usable or an unreliable signal may be an “OFF” flag.

19. Advantages of VOR More accurate & precise flying: Reliable:
The accuracy of course alignment of the VOR is excellent, being generally plus or minus 1 degree.
Reliable:
Can be used day and night.
Multiple number of route :
Provide multiple number of route ‘towards’ or away from each station.
These routes are like invisible highways , which the pilot can navigate to and away from any location.
VOR: Information
AZIMUTH in VOR is a clockwise angle between magnetic
north and the line connecting the VOR and the aircraft. The
indication is displayed on an “Omni Bearing Indicator” in the
aircraft.
The COURSE is the information whether aircraft is flying to
the left or right of, or exactly on the pre-selected course line.
The course information is displayed on a “Flight Path
Deviation Indicator”.
TO-FROM indication tells the pilot whether an aircraft is
approaching to or moving away from VOR stations.
Provides multiple number of courses (invisible highways).
Determine a fix. A pilot can tune two VOR stations and reading of their bearings.
VOR is position sensitive, pilot can fly a straight line without error.
Straight line is achieved by maintaining a line of constant bearing
The aircraft can accurately kept on course.
VOR frequencies are free of static interference and therefore give reliable indicatio

20. Disadvantages of VOR
Signal s can not be received at low altitudes (below 1000ft)
VORs are sensitive to the interference of terrain. The nearest mountains and buildings cause the VOR bearings to be stopped and interrupted.
Other disadvantages is VOR equipments are costly to maintain.

21. VOR as a NAVIGATION AID Ground - monitors
Accuracy: ± 3º
Availability:
(Two transmitters) 99.9%
Integrity:
Ground - monitors
Air- receiver measures signal strength and modulation depth

22. Summery of VOR

23. VHF Omni directional range (VOR)
VHF (very high frequency) is used by air traffic control and operates in the VHF band between 118 and MHz
Range is 30 miles at 1000 feet and approximately 135 miles at 10,000 feet
VHF systems are found in any aircraft capable of two way radio communication and are largely used for controlling traffic.

24. VHF Omni directional range (VOR)
VOR’s operate between to MHz frequency band
System includes
VOR ground station or transmitter
VOR receiver in aircraft
In light aircraft this is often combined with the comm radio
Aircraft display
CDI course deviation indicator
TO/FROM indicator
OBS omni-bearing selector or course selector
ON/OFF flag to determine field strength
Antenna

25. VHF Omni directional range (VOR)
VOR station continually transmits an infinite number of radials.
The VOR receiver in the aircraft receives the signal and operates the visual indicator.
The pilot determines the bearings of VOR station with respect to the aircraft.

26. Syllabus VHF Omnirange, VOR receiver principles
DME distance measuring equipment, Principles of operations
Instrument landing system
Localizer and Glideslope
Give a brief overview of the presentation. Describe the major focus of the presentation and why it is important.
Introduce each of the major topics.
To provide a road map for the audience, you can repeat this Overview slide throughout the presentation, highlighting the particular topic you will discuss next.

27. Distance measuring Equipment

28. DME (Distance Measuring Equipment )
Frequency Band:
Airborne: MHz – 1150 MHz
Ground : 63 MHz below Tx frequency 1025 – 1087 MHz 63 MHz above Tx frequency 1088 – 1150 MHz
This gives 126 channels but two codings are used (X and Y) which doubles the capacity

29. DME
As the name implies , DME provides information on the distance from the aircraft to the ground station
Used to establish position along an airway and also to establish hold points

30. DME Frequency Band: Airborne: 1025 MHz – 1150 MHz (L band)
Ground : 63 MHz below Tx frequency 1025 – 1087 MHz 63 MHz above Tx frequency 1088 – 1150 MHz
This gives 126 channels but two codings are used (X and Y) which doubles the capacity

31. DME General Principle: Airborne transceiver transmits a pair of pulses
(spaced at 12μs for mode X and 30μs for mode Y)
Ground transmitter receives the pulses, waits 50μs and then transmits another pair of pulses back to the aircraft
Airborne transceiver measures the time between transmission and reception, subtracts the 50μs, multiplies by the speed of light and divides by 2.

32. DME
This is very simple but gets more complicated when we want to service more than one aircraft
We need a method of distinguishing among the signals from up to 100 aircraft.
This is done essentially by generating a random set of pulses and correlating with the replies to determine the correct ones.

33. DME AIRBORNE TRANSPONDER

34. DME PULSES

35. DME OUTPUTS Distance Speed Time to Station Notes:
1. The last two are valid only if the aircraft is going
directly towards or away from the ground station.
2. The DME measures SLANT RANGE to the station.

36. DME Distance (Slant Range)
Altitude
DME Distance (Slant Range)
Ground Range

37. DME Ground Station
The ground station simply receives a pulse pair, inserts the 50 μs delay and retransmits it.
To reduce the effects of reflections it will not reply to another interrogation for about 60 μs (dead time)

38. DME Ground Station SQUITTER
The ground station transmits 2700 pulse pairs per second regardless of the number of aircraft interrogating.
The extra pulse pairs are called “squitter”
If there are not enough interrogations to make up 2700 pulse pairs, the ground receiver increases its sensitivity until noise pulses trigger enough replies to make up the difference
If there are too many interrogations, the receiver decreases its sensitivity so that the weakest interrogations get ignored

39. DME Ground Station SQUITTER
Using squitter has the following advantages:
The transmitter average output power is constant
The receiver AGC has a constant average signal to work with
The ground receiver sensitivity is maintained at the optimum level
In the case of overload, the aircraft farthest from the station are dropped off first.

40. DME Using squitter has the following advantages:
The transmitter average output power is constant
The receiver AGC has a constant average signal to work with
The ground receiver sensitivity is maintained at the optimum level
In the case of overload, the aircraft farthest from the station are dropped off first.

41. DME as a Navaid Accuracy:
The ICAO specification for DME is 0.5NM or 3% of distance
Tests done on Canadian DMEs show that their errors are less than 30m.

42. DME as a Navaid Integrity
DME ground stations are equipped with monitors which can detect erroneous delays and out-of-tolerance power output levels. These shut the system down if and error is detected

43. DME as a Navaid Availability:
As with most systems there is a standby transmitter which takes over when the main one fails.
availability is well above 99.9%

44. Summery
Errors
Diagonal (slant-line) distance from station to aircraft – not lateral
Becomes greater the closer you get to the station
Greatest when directly over station at high altitudes
Limited number of queries
Uses
Intersections/Fixes
IAP
Groundspeed
Radio signal sent out from aircraft to ground station. Ground station interprets this signal and sends back. Equipment in aircraft measures time and converts to nautical miles.

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