1. An Introduction to High Frequency Radio Communications and ALE
2018 ORWG Wing Conference
Lt Col David Rudawitz
ORWG Director of Communications

2. Introduction to HF Communications

3. Introduction to HF Communications
HF (High Frequency) is the radio spectrum with frequencies ranging between 1.6 MHz and 30MHz. Within this radio spectrum an efficient mode of transmitter modulation, SSB (Single Side Band), is used.
An HF radio system consists of three basic components,
transmitter/receiver unit (commonly called the transceiver)
Antenna
power source
The transmitting and receiving functions are usually contained in the one unit
Transceiver includes both a microphone and a speaker to allow either function.

4. Introduction to HF Communications
The antenna
Usually consists of a wire or metal rod which is mounted above the ground in a clear space
Connected to the transceiver by means of a coaxial cable.
When the unit is transmitting, the electrical signals it produces travel through the coaxial cable to the antenna, where they are changed into radio waves and radiated.
When the unit is receiving, the antenna receives radio waves, translates them into electrical signals which travel through the coaxial cable and are heard through the receiver as voice signals.

5. Introduction to HF Communications
By combining HF SSB modulation along the Ionosphere, a layer of ionized gases that reside 100KM to 700KM above the Earth's surface, an efficient, cost effective mode of communication can be achieved over short medium and long distances.
In many remote areas, HF/SSB is the only form of communication possible.

6. About HF Communications
Communications on any HF SSB transceiver will sound different to that on a VHF (Very High Frequency) or a UHF (Ultra High Frequency) radio or telephone.
This is because of the nature of HF propagation and the modulation methods used.
On HF transceivers there will always be background noise evident behind the signal you are receiving and this will increase when there is electrical interference or thunder storm activity in the surrounding area.

7. HF Propagation
When HF/SSB radio waves are generated by the transceiver there are three main components:
Ground Wave - which travels directly from the transmitting antenna to the receiving antenna following the contours of the Earth.
Sky Wave - which travels upward at an angle from the antenna until it reaches the ionosphere (an ionised layer above the Earth's surface) where upon it is reflected back down to Earth to the receiving antenna.
Direct Wave (LOS Wave) – this wave may interact with the earth-reflected wave depending on terminal separation, frequency and polarization.

8. HF Propagation

9. HF Propagation – Ground Waves
Generally speaking the Ground Wave is used to communicate over short distances usually less than 50 Km.
Because Ground Waves follow the contours of the Earth it is affected by the type of terrain it passes over.
Ground Waves are therefore rapidly reduced in field strength when they pass over heavily forested areas or mountainous regions.

10. HF Propagation - Sky Waves
Used to communicate over medium to long distances, up to 3000Km.
Whilst it’s nature of propagation eliminates signal reduction from ground terrain factors, as in Ground Waves, the Ionospheric characteristics can affect the received signal quality.
Correct frequency selection is critical to establishing and maintaining reliable communications.

11. HF Propagation - Direct Wave
Line of sight between transmitter and receiver
May interact with the earth-reflected wave depending on terminal separation, frequency and polarization
May not be a dependable way to communicate between two stations.

12. Factors Which Affect HF /SSB Communications
Frequency Selection
Time of Day
Weather Conditions
Man-made electrical interference
Poor system configuration and installation

13. Frequency Selection
Frequency selection is perhaps the most important factor that will determine the success of your HF / SSB communications.
Generally speaking the greater the distance that you wish to communicate over then the higher the frequency you should use.
Frequency Selection Rule:
The higher the sun, the higher the Ionosphere, therefore the higher the frequency used.
The lower the sun, the lower the Ionosphere, therefore the lower the frequency used.

14. Time of Day
Frequencies are normally higher during the day and lower at night.
With dawn, solar radiation causes electrons to be produced in the ionosphere and frequencies increase reaching their maximum around noon.
During the afternoon, frequencies begin falling due to electron loss and with darkness the D, E and F1 regions disappear.
Communication during the night is by the F2 region and absorption of radio waves is lower. Through the night, frequencies gradually decrease, reaching their minimum just before dawn.

15. Using HF During The Day Y Y Y Y Earth's Surface Ionosphere Ground Wave
Skywave Y Y Y Y
Ground Wave C
800Km B
20 Km A D
2000Km
Earth's Surface

16. Using HF During The Night
Ionosphere
Sky Wave Y Y Y Y
Ground Wave C
800Km B
20 Km A D
2000Km
Earth's Surface

17. Skip Zone Y Y Earth's Surface Ionosphere Skip Distance Dead Zone
Skywave
Skip Distance Y Y
Dead Zone
Ground Wave
Receive Station
Transmit Station
Earth's Surface

18. ‘Ordinary’ Propagation
To travel a long distance, the signal must take off at a LOW angle from the antenna
– 30 degrees or less
This is so that it can travel the maximum distance before it first arrives at the Ionosphere
Long gap before signal returns to earth – the part in between this and the end of the ground wave is the so-called Skip (or Dead) Zone

19. Weather Conditions
Certain weather conditions will also affect HF / SSB communications.
Stormy conditions will increase the background noise as a result of ‘static’ caused by lightning.
Atmospheric noise, which is caused by thunderstorms, is normally the major contributor to radio noise in the HF band and will especially degrade circuits passing through the day-night terminator.
Atmospheric noise is greatest in the equatorial regions of the world and decreases with increasing latitude. Its effect is also greater on lower frequencies, hence it is usually more of a problem around solar minimum and at night when lower frequencies are needed.

20. Weather Conditions
In severe stormy conditions this ‘static’ could swamp out the transmitted signal and make the received signal unreadable no matter how good the frequency selection is.

21. Man-made Electrical Interference
Man-made noise includes
Ignition/engine noise,
Neon signs/fluorescent lights,
Electrical cables/power transmission lines,
Generators,
Air-conditioners
This type of noise depends on the technology used by the society and its population.
Interference may be intentional, such as jamming, due to propagation conditions or the result of others working on the same frequency.

22. Man-made Electrical Interference
Man-made noise tends to be vertically polarized, so selecting a horizontally polarized antenna may help in reducing noise.
Using a narrower bandwidth, or a directional receiving antenna (with a lobe in the direction of the transmitting source and a null in the direction of the unwanted noise source), will also aid in reducing the effects of noise.
Selecting a site with a low noise level and determining the major noise sources are important factors in establishing a successful communications system.

23. System Configuration and Installation
The method in which your system is configured and installed will also affect the success of your HF SSB communications. Your choice of antenna and power supply is critical. Correct installation is also extremely important.
Failure to correctly install a HF / SSB system will greatly affect the communications quality you will obtain.

24. NVIS Near Vertical Incident Skywave

25. NVIS What is NVIS ? Means Near-Vertical Incidence Skywave
Opposite of DX (long – distance)
Local - to - Medium Distance (0 – 250 or more)

26. ‘Ordinary’ Propagation

27. NVIS Propagation
To travel a local - medium distance, the signal must take off at a HIGH angle from the antenna – typically 60 – 90 degrees
This returns from the Ionosphere at a similar angle, covering 0 – 250 mls
It thus fills in the Skip (or Dead) Zone – like taking a hose and spraying it into an umbrella !

28. NVIS Propagation

29. Using NVIS Successfully
HIGH angle of radiation from antenna
Minimise ground wave, as it will interfere with the returning skywave
Most importantly, CHOOSE THE CORRECT FREQUENCY BAND
Go too high in frequency and your signal will pass through straight into space!

30. Choosing the right frequency
The Ionosphere – D, E, F1 & F2 layers
D and to a lesser extent, E layers attenuate and absorb signal
Best returns from F2 layer
At any one time we need to know the frequency of the F2 layer – The Critical Frequency or foF2
Optimum frequency for NVIS work around 10% below this

31. The Ionosphere

32. NVIS - Frequency and Time
In practice,
Highest NVIS frequency can reach 10 MHz band
Lowest can go down to 1.81 MHz band
During the day
‘Higher’ frequency band during day,
‘Middle’ frequencies afternoon/evening,
‘Lower’ frequencies at night
Frequencies also affected by time of year and period of sunspot cycle
For best results, these three different frequency ‘bands’ required

33. NVIS – The Critical Frequency
The Critical Frequency is the key to successful NVIS working
The Critical Frequency (or foF2) is the highest frequency at any one time that a signal transmitted vertically will be returned to earth. Anything above this passes into Space.
Sometimes refered to as the Maximum Usable Frequency (MUF)
As we are interested in vertical signals for NVIS, then the value of the Critical Frequency (foF2) at any one time is of great importance to us
How can we find or estimate foF2 ?

34. HF-ALE

35. ALE To The Rescue What Is ALE? What Does ALE Require?
How Does ALE Work?
How Is ALE Implemented?
ALE Advantages
ALE Hazards

36. What is ALE Automatic Link Establishment Four S’s
Smart radio
Suite of frequencies to form a net
Sounding other stations in the net
Selecting the best frequency for transmitting to the desired station
Improved operational capability without requiring specialized knowledge of propagation

37. What Does ALE Require? Smart Radio with station monitor 24/7
Frequency Suite across HF spectrum
Unique Digital Callsign for each station
Broadband antenna or tuner modified for ALE

38. How Does ALE Work? Radio scans all frequencies in the net
Radio can transmit (sounds) on all net frequencies and logs responding stations ~ every 90 min
Radio receives and responds to soundings from other stations in net
Radio maintains data base of responding stations
Callsign
Frequency
Link quality (signal strength)
No operator required

39. Automatic Link Establishment (ALE)
1. You configure a peer-to-peer network among your radios
Completely inside the radios - no infrastructure between them
Program a common network ID
Program individual site IDs
Program the authorized group of HF frequencies
Hook up the antennas, turn on the radios, and let them take off !
MyNet
MyNet
Site 1 F1 F2 F4 F3 F5 F6
Site 2
MyNet
MyNet
Site 3
Site 4

40. Automatic Link Establishment (ALE)
2. The radios build a dynamic model of the optimum pathways
Each radio tests with every other radio on every frequency
Results are saved on each radio by time of day
scan F1
scan
MyNet
MyNet
Site 2, how do you copy
Site 1 on F1?
I copy you just fine. How do you copy me? F2
Site 1
Site 2 F3 F4
Fine also, let’s try F2 now
F2 is ok, but not great F5
OK, how about F3 F6
No reply from Site 2
MyNet
MyNet
Site 3
Site 4
scan
scan

41. Automatic Link Establishment (ALE)
3. A non-technical user places a call like on a telephone
The radio remembers the best frequency and places a call
The radios handshake, change frequency if needed, then connect
The receiving radio(s) ring like a telephone.
People talk over hundreds of miles with zero infrastructure!
scan F1
scan
MyNet
MyNet
Digital callout with Network ID, Site ID(s), other info
Scan stops and the receiver recognizes its Site ID F2
Site 1
Site 2 F3
Handshake, connect
Handshake, connect F4 F5
MyNet
RING !!
MyNet F6
Site 3
Site 4
scan
scan

42. CAP ALE Implementation
Designated Region &Wing Stations maintain constant ALE net
Message Center Stations (MCS)
Other stations join net for specific operational missions
Region/Wing nets are established
Standardized ALE selfID system
Voice call sign numbers restricted to 00-99

43. CAP Self ID Wing selfIDs: xxxxwgCAP Region callsign: xxxregCAP
xxxx = wing assigned number (does not have to match call sign and must be between 00-99)
MSC uses “0000wgCAP”
Leading zeros to make 4 digits
wg = Wing 2 digit postal code
Region callsign: xxxregCAP
xxx = region callsign (leading zeros if needed)
reg = 3 letter region designator
MSC uses “000regCAP
Examples
0077ORCAP for BeaverFox 77
004PCRCAP for PCR station

44. ALE Advantages
Operator not involved in establishing data base of usable frequencies
Operator not required to monitor for incoming calls – No static background noise
Selection of calling frequency done by radio
No guessing what frequency the other station is on
Different frequencies may be used to contact multiple stations in different areas

45. ALE Hazards All existing HF hazards exist PLUS
Spontaneous soundings transmit without operator command
Mobile installations have added hazards
Closer proximity of personnel to antenna
Whip antenna poses poking hazard
Radio off during vehicle servicing

46. Advanced HF/ALE Systems and Networks
Features
Configuration flexibility
Selective Call
Frequency hopping
Secure call
GPS tracking
Digital Signal Processing
Built-in Test Equipment (BITE)
Automated interconnects for:
, Fax, Data, SMS
PSTN Direct Dial
VHF, UHF, 700, 800, and other bands
Other OEM equipment

47. Any Questions ?