An Introduction to High Frequency Radio Communications and

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

Introduction to HF Communications

Introduction to HF Communications HF (High Frequency) is the radio spectrum with frequencies ranging between 1. 6 MHz and 30 MHz. Within this radio spectrum an efficient mode of transmitter modulation, SSB (Single Side Band), is used. Ø An HF radio system consists of three basic components, Ø § transmitter/receiver unit (commonly called the transceiver) § Antenna § power source Ø The transmitting and receiving functions are usually contained in the one unit § Transceiver includes both a microphone and a speaker to allow either function.

Introduction to HF Communications Ø 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. Ø 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. Ø

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

About HF 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. Ø This is because of the nature of HF propagation and the modulation methods used. Ø 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. Ø

HF Propagation Ø When HF/SSB radio waves are generated by the transceiver there are three main components: 1. 2. 3. 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.

HF Propagation

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

HF Propagation - Sky Waves Used to communicate over medium to long distances, up to 3000 Km. Ø 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. Ø Correct frequency selection is critical to establishing and maintaining reliable communications. Ø

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

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

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

Time of Day Frequencies are normally higher during the day and lower at night. Ø With dawn, solar radiation causes electrons to be produced in the ionosphere and frequencies increase reaching their maximum around noon. Ø During the afternoon, frequencies begin falling due to electron loss and with darkness the D, E and F 1 regions disappear. Ø Communication during the night is by the F 2 region and absorption of radio waves is lower. Through the night, frequencies gradually decrease, reaching their minimum just before dawn. Ø

Using HF During The Day Ionosphere ave w y Sk Y A Ground Wave Y Y B C 20 Km 800 Km Earth's Surface Y D 2000 Km

Using HF During The Night Ionosphere e Wav y k S Y A Ground Wave Y Y B C 20 Km 800 Km Earth's Surface Y D 2000 Km

Skip Zone Ionosphere ve a w y Sk Skip Distance Y Transmit Station Ground Wave Dead Zone Earth's Surface Y Receive Station

‘Ordinary’ Propagation Ø 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 Ø 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 Ø

Weather Conditions Ø 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 will especially degrade circuits passing through the day-night terminator. Ø 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. Ø

Weather Conditions Ø 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.

Man-made Electrical Interference Ø 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. Ø Interference may be intentional, such as jamming, due to propagation conditions or the result of others working on the same frequency. Ø

Man-made Electrical Interference Man-made noise tends to be vertically polarized, so selecting a horizontally polarized antenna may help in reducing noise. Ø 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. Ø Selecting a site with a low noise level and determining the major noise sources are important factors in establishing a successful communications system. Ø

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. Ø Failure to correctly install a HF / SSB system will greatly affect the communications quality you will obtain. Ø

NVIS Near Vertical Incident Skywave

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

‘Ordinary’ Propagation

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

NVIS Propagation

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

Choosing the right frequency Ø Ø Ø The Ionosphere – D, E, F 1 & F 2 layers D and to a lesser extent, E layers attenuate and absorb signal Best returns from F 2 layer At any one time we need to know the frequency of the F 2 layer – The Critical Frequency or fo. F 2 Optimum frequency for NVIS work around 10% below this

The Ionosphere

NVIS - Frequency and Time Ø In practice, § Highest NVIS frequency can reach 10 MHz band § Lowest can go down to 1. 81 MHz band Ø 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 Ø For best results, these three different frequency ‘bands’ required Ø

NVIS – The Critical Frequency is the key to successful NVIS working Ø The Critical Frequency (or fo. F 2) is the highest frequency at any one time that a signal transmitted vertically will be returned to earth. Anything above this passes into Space. Ø § 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 (fo. F 2) at any one time is of great importance to us Ø How can we find or estimate fo. F 2 ? Ø

HF-ALE

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

What is ALE Automatic Link Establishment Ø Four S’s Ø § § Ø 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

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

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

Automatic Link Establishment (ALE) Ø 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 ! My. Net Site 1 F 1 My. Net Site 2 F 3 F 4 My. Net F 5 My. Net Site 3 F 6 Site 4

Automatic Link Establishment (ALE) Ø 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 My. Net Site 1 scan Site 2, how do you copy Site 1 on F 1? F 1 scan F 2 I copy you just fine. How do you copy me? F 3 Fine also, let’s try F 2 now F 4 My. Net Site 2 F 2 is ok, but not great F 5 OK, how about F 3 F 6 No reply from Site 2 My. Net Site 3 My. Net scan Site 4

Automatic Link Establishment (ALE) Ø 3. A non-technical user places a call like on a telephone § § My. Net Site 1 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 Digital callout with Network ID, Site ID(s), other info scan F 2 Scan stops and the receiver recognizes its Site ID F 3 Handshake, connect My. Net Site 3 F 1 F 4 Handshake, connect F 5 RING !! F 6 scan My. Net Site 2 My. Net Site 4

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

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

ALE Advantages Ø Ø Ø 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

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

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