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“Alone at sea, beneath a sky without end and surrounded by an ocean without mercy, the faint crackle of an SSB radio is more than a signal. It is a reminder that somewhere beyond the horizon, the world is still listening.” – MJ Martin

Introduction

During a recent fun conversation, I met a woman who was a very experienced sailor with worldwide travels. She continually used the term HAM radio when referring to the SSB radio on her sailboat. I have never thought of the SSB radio as a HAM radio. But I suppose there is some validity to her comments.

I too have sailed globally, albeit not as extensively as this new acquaintance. But I pride myself on being a learning person and took many hands-on courses and read deeply into nautical studies. I earned numerous certifications for coastal navigation, celestial navigation, offshore cruising, and more, as well as I acquired a deep comprehension on all of the technical systems and devices onboard – including the SSB radio.

Two weeks later, the issue of SSB vs HAM radios is still stuck in my head, so I decided to take a deep dive into the subject matter to clarify my own thoughts related to the use of terminology and technology. Here is what I learned.

Marine SSB and terrestrial HAM radio are often compared because both can use Single Sideband, or SSB, modulation on HF frequencies. Technically, however, they are not the same kind of thing. SSB is a modulation method. Marine radio and amateur, or HAM, radio are two different regulated radio services.

The more meaningful comparison is therefore between Marine HF/SSB radio and terrestrial Amateur HF/SSB radio, particularly when considering communications range.

Marine SSB Radio

Marine SSB is designed for long-distance communications between vessels and shore stations, or between vessels operating beyond the practical range of marine VHF. Marine VHF is primarily a line-of-sight system. Depending on antenna height, vessel size and local conditions, practical communications range is often approximately 20 to 50 nautical miles, although greater distances are possible between high antennas.

Marine SSB operates differently. By using frequencies in the MF (Medium Frequency band between 300 kilohertz (kHz) and 3 megahertz (MHz)) and the HF (High Frequency band between 3 MHz and 30 MHz) spectrum, a marine SSB signal can propagate far beyond the radio horizon.

Depending on frequency, time of day, solar conditions, antenna performance and atmospheric conditions, communications can extend from a few dozen nautical miles to hundreds or thousands of kilometres. This makes HF SSB particularly valuable for offshore and ocean-going vessels. A vessel hundreds of kilometres from land may therefore be well beyond VHF coverage while still being capable of communicating by HF SSB.

How Marine SSB Achieves Long Range

Marine SSB can use several propagation mechanisms. At lower MF and HF frequencies, ground-wave propagation can provide useful communications beyond normal VHF line-of-sight distances. At greater distances, the dominant mechanism becomes skywave propagation. The transmitted HF signal travels upward toward the ionosphere, where it is refracted back toward Earth. The signal may then return hundreds or thousands of kilometres from the transmitter. Multiple ionospheric hops can extend communications across oceans and even between continents.

In practical terms, a properly installed marine SSB system can potentially communicate:

  • 50 to 200 nautical miles using lower-frequency propagation under suitable conditions.
  • Several hundred nautical miles using regional HF propagation.
  • 1,000 to several thousand nautical miles using ionospheric skywave propagation.

These are not guaranteed distances. HF radio does not behave like a cellular network with a fixed coverage boundary. Range varies continuously with propagation conditions.

Terrestrial HAM Radio Range

Terrestrial HAM operators use the same fundamental HF propagation mechanisms. A HAM operator using an HF transceiver and SSB may communicate locally, regionally, nationally or internationally. For example, an amateur operator in Ontario using the 40-metre band might communicate with another station several hundred kilometres away during suitable conditions. The same operator using the 20-metre band might communicate with Europe, western Canada, the Caribbean or other parts of the world. Under favourable propagation conditions, a modest amateur station using approximately 100 watts can communicate several thousand kilometres. With efficient antennas and favourable ionospheric conditions, worldwide communications are entirely possible. Therefore, neither marine SSB nor amateur HF radio has a simple maximum range. Their ultimate range is determined much more by propagation and antenna efficiency than by transmitter power alone.

Frequency Determines Range Behaviour

HF radio range is strongly influenced by the operating frequency. Lower HF frequencies generally perform better during nighttime conditions and over shorter or intermediate regional distances. Higher HF frequencies often perform better during daylight and can support very long-distance communications when ionospheric conditions are favourable. This is why both marine and amateur HF operators use multiple frequency bands. A marine vessel might move between the 4, 8, 12 and 16 MHz maritime bands as conditions change. An amateur operator might similarly move between the 80, 40, 20, 15 and 10-metre amateur bands. The objective is essentially the same: choose a frequency that matches the desired communication distance and current ionospheric conditions.

The Skip Zone

One unusual characteristic of HF communications is that greater range does not always mean better local coverage. A skywave signal may leave the transmitting antenna, travel into the ionosphere and return to Earth hundreds of kilometres away. The area between the end of useful ground-wave coverage and the point where the skywave returns can experience weak or nonexistent reception. This is known as the skip zone. Consequently, an HF station might successfully communicate with someone 1,000 kilometres away while having difficulty communicating with another station only 200 kilometres away. This characteristic applies equally to marine and amateur HF communications.

Antenna Systems Make a Major Difference

Transmitter power alone does not determine range. The antenna system is often more important. A terrestrial HAM operator may have the luxury of installing a resonant dipole, vertical antenna, directional beam or large tower-mounted antenna array. A vessel has much greater physical constraints. Marine installations commonly use a long insulated backstay or a vertical whip connected through an automatic antenna tuner. Because these antennas are often electrically short compared with the wavelength being transmitted, installation quality becomes critical. Grounding, counterpoise design, antenna tuner location, feedline losses and vessel construction can significantly influence effective radiated power. A poorly installed 150-watt marine SSB system can therefore perform worse than a properly designed 100-watt amateur station. The important quantity is not simply transmitter output power. It is how much useful RF energy actually reaches the antenna and is radiated in the desired direction.

Marine SSB Versus Marine VHF

The greatest practical advantage of marine SSB becomes apparent when comparing it with marine VHF. A typical VHF marine radio operating near 156 MHz depends heavily upon antenna height because the signal generally travels close to line of sight. A vessel may therefore obtain perhaps several tens of nautical miles of reliable direct range. HF SSB behaves very differently. The ionosphere effectively becomes part of the communications system. Instead of being limited by the curvature of the Earth, the signal can travel upward and return to Earth far beyond the horizon.

The difference can therefore be dramatic:

  • Marine VHF: typically tens of nautical miles.
  • Marine HF SSB: potentially hundreds to thousands of nautical miles.

This is why HF SSB historically became such an important communications technology for offshore vessels.

Marine SSB Versus HAM Radio

From a pure RF engineering perspective, there may be surprisingly little difference between an HF marine SSB transmission and an HF amateur SSB transmission.

Both can employ:

  • Single Sideband suppressed-carrier modulation.
  • Approximately 2.4 to 3 kHz voice bandwidth.
  • HF propagation.
  • Similar transmitter power levels.
  • Ionospheric skywave propagation.
  • Large or electrically significant antenna systems.
  • The fundamental physics controlling range are therefore essentially the same.
  • The primary differences are the frequency allocations, licensing requirements, operating rules, equipment configuration and purpose of the communications.
  • Marine SSB operates on authorized maritime frequencies and is intended principally for maritime communications.
  • HAM radio operates within amateur allocations and supports communications, technical experimentation, emergency communications and radio science.

There Is No Fixed Maximum Range

Perhaps the most important concept is that an HF radio does not have a range rating comparable to a handheld radio, Wi-Fi access point or cellular tower. Saying that an HF SSB radio has a range of “500 kilometres” would therefore be misleading. On one frequency at one time of day, reliable range might be only a few hundred kilometres. Several hours later, changing propagation could allow the same radio and antenna to communicate several thousand kilometres away. Conversely, a frequency that worked extremely well yesterday may perform poorly today. HF communications are therefore fundamentally a link-budget plus propagation problem.

  • Transmit power matters.
  • Receiver sensitivity matters.
  • Noise floor matters.
  • Antenna efficiency matters.
  • Frequency matters.
  • Solar activity matters.
  • Time of day matters.
  • Season matters.
  • Geographic location matters.

The ionosphere ties all of these variables together.

The Bottom Line

Marine SSB and terrestrial HAM radio can achieve remarkably similar long-distance performance because they rely on the same fundamental HF radio physics. A marine SSB installation can communicate from tens of nautical miles to thousands of nautical miles depending upon the frequency and propagation conditions. A terrestrial HAM HF station can achieve essentially the same geographic ranges. The difference is not that one technology inherently travels farther than the other. The difference is how each radio service is designed, regulated and used. Marine SSB is optimized for dependable communications involving vessels operating beyond normal VHF range. HAM radio provides licensed amateur operators with access to multiple bands and modes for communications, experimentation and technical development.

A useful way to summarize the distinction is:

  • Marine VHF communicates primarily to the horizon.
  • Marine SSB can communicate beyond the horizon.
  • HAM HF radio can do the same thing because it uses the same ionosphere.

The ocean does not give marine SSB its extraordinary range. The atmosphere above it does.

About the Author:

Michael Martin is the Vice President of Technology with Metercor Inc., a Smart Meter, IoT, and Smart City systems integrator based in Canada. He has more than 40 years of experience in systems design for applications that use broadband networks, optical fibre, wireless, and digital communications technologies. He is a business and technology consultant. He was a senior executive consultant for 15 years with IBM, where he worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).

Martin served on the Board of Directors for TeraGo Inc (TGO: TSX) and on the Board of Directors for Avante Logixx Inc. (XX: TSX.V).  He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology. He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now Ontario Tech University] and on the Board of Advisers of five different Colleges in Ontario – Centennial College, Humber College, George Brown College, Durham College, Ryerson Polytechnic University [now Toronto Metropolitan University].  For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section. 

He holds three master’s degrees – in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and seven major certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has completed over 80 next generation MOOC (Massive Open Online Courses) [aka Micro Learning] continuous education programs in a wide variety of topics, including: Economics, Python Programming, Internet of Things, Cloud, Artificial Intelligence and Cognitive systems, Blockchain, Agile, Power BI, Big Data, Design Thinking, Security, Indigenous Canada awareness, and more.

Martin is a volunteer, a photographer, a learner, a technologist, a philosophizer, and a romantic optimist.