1. Radio and Navigational Aids
LECTURE 3

2. Objectives Introduction to various types of antenna used in aviation
Introduction to frequency used in aviation and their characteristics

3. Antenna
An antenna is a device which provides means for radiating or receiving radio waves.
In communication link, the transmitter is connected through a cable to one antenna, the signal is radiated to another antenna, and then passes through another cable to the receiver.
Communication between aircraft and airfields must use free space propagation, as do radar and navigation systems.
Broadcast systems such as TV or radio can used one transmitter to serve many receivers via a free space link.

4. Electromagnetic Wave propagates
Illustration
Electromagnetic Wave propagates
Transmitting antenna
Receiving antanna
FREE SPACE
Tx line

5. Antenna as transition device
Wire Antennas
Printed Circuit Antenna
HF notch antenna is a portion of metal at the base of the tailfin is replaced by fibreglass so that a loop antenna can be formed. It is clearly aerodynamically suitable.
At UHF and VHF, ‘blade’ antenna are used, which are essentially monopoles made with a a flat sheet rather than a cylinder. The antenna is encased in a fibre glass shell which is shaped for minimum aerodynamic resistance. This shell also acts as the antenna ‘radome’.
Radome = protect an antenna from weather or wind erosion while still allowing antenna to radiate.
Usually placed at the top tail fin
Printed antenna are often used for satellite communications and navigation systems, because they can be mounted on aircraft skin.
An aircraft nose cone may be replaced by a fibre glass radome containing a small microwave reflector antenna which can be rotated vertically and horizontally for use as a forward-looking radar antenna.

6. Types of antenna
Reflector antenna
Array Antenna
Aperture antennas

7. Why choose a correct antenna?
Other than receiving and transmitting energy, an antenna in an advanced wireless system is usually require to optimize the radiation energy in some directions.
For wireless communication systems, the antenna is one of the most critical components.
A good design of the antenna can relax system requirements and improve overall system performance
e.g: A TV for which the overall broadcast reception can be improved by utilizing a high performance antenna.

8. Antenna on Aircraft
Type and size of antenna varies with the different types of aircraft.
The location of antenna depends on the design of aircraft.

9. Discussion on frequencies used for aviation

10. Frequency Band LF 3 0– 300kHz MF 300kHz– 3MHz HF 3 – 30MHz VHFS E
Band
Frequency LF
3 0– 300kHz MF
300kHz– 3MHz HF
3 – 30MHz
VHF
30 – 300MHz
UHF
300MHz– 3GHz
These adjectival designations are convenient in referring to transmission in those bands allocated for radiocommunication by aircraft.

11. Frequency Band
The use of the various Radio Frequencies all over the World is allocated by ITU (International Telecommunications Union.
The Radio Frequencies are being used in various field, amongst them include :
FM Radio Broadcast
Television Broadcast
Land Mobile Stations (Emergency, Business, and Military)
Amateur Radio
Marine Communications
AIRCRAFT COMMUNICATIONS
AIR TRAFFIC CONTROL
AIR NAVIGATION SYSTEMS (e.g.VOR/DME,NDB)

12. VLF-Very Low Frequency
Can be used for communication with submerged submarines and they have some use for this purpose aboard aircraft.
VLF were very important to air navigation years ago, but became increasingly less important as more reliable systems operating at higher frequencies were developed and became widely available.

13. HF-High Frequency HF-High Frequency (3– 30 MHz)
HF: This is the basic band for long-range communications, mainly because its transmissions are reflected from the ionosphere.
HF1 = Typically used for Long-Range ATC communications
HF2 = Back up to HF1. (frequently used to listen to the BBC to overcome boredom on longer flights)
High Frequencies were widely used for domestic aircraft voice communications years ago.
Nearly all that traffic moved to Very High Frequencies long ago and domestic aircraft use of Medium Frequencies is now very rare.
However, international flights still use the High Frequencies bands routinely for voice communications, because of the much longer distances over which they can be used. All these frequencies can be received by the receiver at this website.

14. HF transmissions are reflected from the ionosphere.
HF-High Frequency
HF undergoes the “Skywave” phenomena where ionosphere refracts the HF radio waves and can be utilized for medium and long range radio communications,
HF transmissions are reflected from the ionosphere.

15. Disadvantage of HF Efficiency of HF is affected by:
All kinds of electrical interference caused by ionosphere disturbances such as thunderstorms. This provides the typical radio noise.
Other weather phenomena:
Sunlight
Season
Solar Activity

16. VHF: Very High Frequency
VHF-Very High Frequency (30 – 300MHz)
Normally, VHF between 100 to 200MHz are used for ATC communications, emergency and navigational aids (VOR, DME, ILS).
VHF1 = Used for ATC communications
VHF2 = Emergency frequency monitoring.
VHF3 = Typically used for Data transmissions (ACARS).
VHF: This is the standard air traffic control band using speech modulation. It is limited to LOS, ‘line of sight’ range, normally about 200km. The lower end, MHz, is restricted to VOR/ILS functions, the remainder is used for civil aviation.
All VHF can be used interchangeably for any VHF purposes.

17. Characteristics of VHF Radios
The propagation characteristics of VHF are optimized for short range communications.
The range varies depending the atmospheric conditions but normally is about nautical miles.
However it is more prone to blockage by Land Features, buildings, and its lower spectrum frequencies.

18. Airport Ground control
Specific Usage
VHF Voice communication Source Carrier
MHz
Air Traffic Control
121.5 MHz
Emergency
121.6 – MHz
Airport Ground control
123.1 MHz
Search And Rescue
MHz
Air traffic control
MHz
En Route
MHz
Shows block diagram of AM radio transmitter for speech communication. Source carrier and information (voice) are modulated

20. The use of VHF for Aeronautical Communications in Malaysia
In Malaysia the use of VHF Radio Systems for Aviation purposes are wholly owned by DCA Malaysia and are stationed on various Hill Stations owned by Telekom Malaysia

21. UHF: Ultra High Frequency
UHF-Ultra High Frequency (300MHz– 3GHz)
UHF: similar to VHF, but is restricted mainly for military aviation use.
In Malaysia, UHF is mostly used by Combat Aircraft of the Royal Malaysian Air Force (RMAF).
Other applications includes Navigations/Landing Aids such as the Glide path component of the ILS(Instrument Landing Systems).

22. UHF: Ultra High Frequency
UHF broadcasting was used outside Kuala Lumpur and the Klang Valley by private TV station TV3 in the late 80’s with the Government stations only transmitting in VHF (Bands 1 and 3).
At current count, there are 4 distinct UHF signals receivable by an analog TV set in the Klang Vall, Channel 25 (8TV), Channel 29 (TV3 UHF Transmission), Channel 37 (NTV7) and Channel 39 (TV9). Channel 35 is usually allocated for VCR,s, decoder units (i.e.the ASTRO and MiTV set top boxes) and other devices that have an RF signal generator (i.e. consoles).

23. Question
Names two types of two way communication radios (frequencies) used on an aircraft?
What are their purposes?
List the benefit of the new communication system for passengers.(broadband for surfing the net,SMS,and phones.)

24. Benefit of the new communication system for passengers
Some of the benefits of passengers are the broadband, SMS, Phones, these are good to keep business travelers well into their schedules, this allows them to work while they fly, and this alleviates the problems once they land, they can track their flights, know exactly when they will land, etc...

25. Onboard Communications
Radio is the choice of communications medium for air to ground communications, but there are requirements for considerable onboard communications. such applications as voice communications among flight crew members between flight crew members and passengers.
This communication is provided by a system called an interphone and usually works in conjunction with an audio panel, which not only provides the interphone function but switches speakers and headphones between the various communications and navigation systems aboard the aircraft.

26. Audio Panel
A number of audio sources in the aircraft that the flight crew should monitor
Different transceivers for communication
Navigation equipment (for station identifier)
ADF, VOR, DME, MLS
Surveillance equipment – TCAS
Method of selecting which navigation systems will be heard on headphones/speaker
Use audio control panel

27. Example of a control panel
The figure shows two rows
One row selects sources for speaker
Another row selects sources for the headphones
Other sources that does not require any switching includes
Voice warning signals from the collision avoidance system and the marker beacon used of instrument landing
Audio control panel must provide switching for the communications transceiver transmit function
Normally there are 2 transceiver and on can be controlled from the microphone
The audio panel is a very critical piece of equipment aboard the aircraft. Since all the audio sources pass through the audio panel, a failure in the audio panel can cause a serious problem.
Therefore, many audio control panels have an emergency mode.
The emergency mode permits bypassing the audio panel and allows one transceiver to be operated.
In many cases, since the speaker amplifier is in the audio panel, there will be no cabin speaker and headphones must be used.
To reduce the likelihood of an audio panel failure, many larger aircraft provide two audio panels, one for the pilot and a second for the first officer