HF Radio Basics

You just bought a boat with an HF Radio. What do you do now?

Almost all cruising boaters, even the ‘newbies’, are familiar with their Marine VHF radio and the role it serves in both boating safety and cruising culture. And while most experienced ocean cruisers are quite familiar with VHF’s big brother, HF radio, many new boaters are new to long range radio communication. This article is for you.

Like VHF, many services use HF Radio. These include the military of most countries, merchant vessels, long range aircraft, the civil air patrol, and amateur radio operators around the world. Services on HF are similar to those on VHF. In all likelihood you already have at least a fixed VHF radio and probably one or more hand-held units on your boat. The fixed radio would be connected to a GPS to provide DSC calling and automatic emergency calls with your position. Modern HF radios have exactly the same sort of DSC calling and emergency operation with a twist: they can send a M’aidez (May Day) on five frequencies at once to make sure someone is in range.

To understand the differences between VHF-FM Marine Radio and HF-SSB Marine Radio, we need to cover some of the basics of radio science and technology. For those who find this interesting, there is an entire separate hobby in amateur (ham) radio; however, this article will be limited to using a marine HF radio, sometimes called an SSB Radio on your boat as you cruise. As we don’t refer to our VHF radios as FM radios, in this article we will refer to HF radios, like VHF, by the frequencies they transmit on and not their primary voice operating mode.

Keeping Legal 1

In order to operate a Marine HF radio, US Flagged Vessels will require a minimum of a ship’s station license and an operator’s license. Both are issued by the FCC. The station license is good for 10 years and includes your “Call Sign†and your MMSI Number. You probably already have this, as it is also required to operate your VHF radio outside of the US. If you don’t have a ship’s station license, you’ll need to apply for one at the FCC on Form 605. You will also need at least a “Restricted Radio Operators Permit†(RROP). This is good for life and does not require an examination.

Let’s get technical for a minute. Webster defines as “the transmission and reception of electromagnetic waves of radio frequency, especially those carrying sound messages.†For our purposes we are referring to the ways in which we can “modulate†a high frequency radio wave that permits us to both talk to other radio operators and to send and receive data – including emails and weather information – to and from other boats and shore stations.

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HF, VHF, and the Frequency Spectrum

All radio transmissions take place somewhere along the “Frequency Spectrum,†the term used to describe the range of sound, radio, and light waves. This ranges from audible sounds (which we can hear) to radio waves to light waves (which we can see). HF Radios operate in 3-30mhz (millions of cycles per second) while VHF radios operate in the 30-300mhz range. By comparison, you can hear sounds in the 20-20,000hz range. In addition to requiring different technology to send and receive signals, HF and VHF waves behave very differently in the atmosphere. While VHF communication is largely limited to “line of sight†between two stations, HF radio waves can reflect off of a charged portion of the atmosphere called the ionosphere and reflect back to earth much further away. You have probably heard distant AM radio stations at night and may have listened to shortwave radio broadcasts. This sort of long range propagation will be discussed in much greater detail later on.


When we say we are using an SSB Radio, we mean we are using a High Frequency Radio and Single Sideband Modulation. When we use our VHF radio, we are using Frequency Modulation, just like the FM radio and Television. SSB is a special kind of AM in which we don’t transmit all of the signal, just one half of it, called the Upper Sideband (USB). Single Sideband has several advantages over traditional AM, which could be considered modulated carrier dual sideband. With Single Sideband (SSB) we can suppress the actual carrier AND one half of the single (the Lower Side Band) and still convey all of the necessary voice information. This allows us to have more people using more channels in the same area of the band (compared to broadcast AM, for example). Also, more actual radio power is behind the voice signal itself. For these reasons, SSB is an outstanding operating mode for HF voice communication. To be clear, on the marine bands we only use Upper Sideband (USB). Ham operators also use the Lower Sideband (LSB), but all Marine HF/SSB radios use USB only. Like our VHF radios, we have both ‘simplex’ channels, where you transmit and receive on the same frequency, and ‘duplex’ channels, where you transmit on one frequency and receive on another. IF someone says they are using Chanel 6A, for example, they will be operating on 6.224mhz (simplex) using USB. Marine HF/SSB Frequencies range from 4mhz to 25mhz. Like VHF, some are assigned for specific purposes and some are for general communication between boats and licensed shore stations.


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Here is where the differences between HF and VHF radio are most apparent. While VHF signals are line of sight and go straight ahead, either from boat to boat or boat to shore, (or up in the air to airplanes or even the International Space Station), HF radio waves, as noted earlier, are often reflected down to earth much further away. Depending upon the frequency of the signal and the time of day, these signals can travel all the way around the world.

Depending upon your frequency, you may “skip†over nearer stations but be clearly heard by those further away. We call the close in (line of sight) signals Ground-wave and those we reach by skipping off the ionosphere Sky-wave. The stations we “Skip Over†are said to be in the “Skip Zone.†When you log into marine nets you will find many stations offering to “relay†for you if the station you are calling can’t hear you. You may be in Florida and wish to call a station in the Abacos. That’s too close, but a station in Virginia might hear you both and pass your “traffic.†One of the wonders of HF radio is how far signals can propagate, even if you can’t hear them “close in.â€

Another article will focus on which frequencies are best at which times. For now know that 4mhz and 6mhz are good for shorter range (300-600 miles) and higher frequencies such as 8mhz, 12mhz, and 16mhz, are better for longer range communication, such as transatlantic cruising. Note that SSCA maintains radio networks on both 8.104mhz and 12.350mhz from our station KPK. This station can offer support to cruisers from the Canadian Maritimes to Panama and across the Atlantic.

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A Typical Radio Installation

A Marine HF radio installation consists of the radio itself (these days most likely an Icom M802), an antenna tuner (sometimes called a coupler), an antenna, an antenna ground or counterpoise, a power supply, and the necessary cabling between these elements. Many operators add a Pactor modem to send and receive texts, weather images, and other documents. A second article here covers more of doing your own installation; for our purposes we are assuming the radio is already installed on your boat. It should be powered by large wires (6awg at least) directly from the house battery bank (not the distribution panel), have good quality coax cable between the radio and the tuner, and have the tuner connected to the antenna with good, high quality, high voltage wire such as GTO-015.

Most sailboats use an insulated backstay for their antenna, while most power cruisers opt for a 23′ vertical whip. Both can provide an excellent signal when properly installed.

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Keeping Legal 2

Many cruisers also have “Ham Radio†licenses. These are completely different from the Marine Radio licenses mentioned above. Ham radio is wonderful afloat and provides a great deal of camaraderie among other cruisers, but ham radios are not marine radios. While they both use SSB on the HF frequencies, Marine radios are built to a much higher standard. It is illegal to use a radio on the marine frequencies that is not “type approved†by the FCC Part 80 for the purpose. That said, it is perfectly acceptable to use a marine radio on the ham frequencies if the operator is properly licensed.

Basic HF Radio Operation

The easiest way to test your radio is to turn to one of the common marine radio nets. Tune your radio to the frequency before the net starts and press the “antenna tune†button to be sure you are ready to transmit. On the East Coast of the US these include SSCA’s KPK net at 0815ET on 8.104mhz (USB) and the Cruizheimers Net every morning at 0830 ET on 8.152mhz (USB). These and many other nets operate in much the same fashion. After listening for a bit you’ll get the hang of it. They first ask for emergency traffic, then they may have some announcements. When they ask for boats to check in, just give your boat name and wait to be called. Don’t be shy – tell them it’s your first call. Everyone wants to help the new folks–welcome to the wonderful world of HF Radio!

Comments on this article and other technical matters are welcomed in the Tech Talk Forum on the SSCA website at www.ssca.org. As a member, you can opt into this special interest forum by going to:

MemberProfile-> Forums-> ForumMemberships-> AvailableForums-> SSCATechTalkForum.

Click the green icon to the right of the forum name to subscribe. When the pencil icon appears, click it to manage your forum preferences. If you have issues subscribing, contact Home Base at [email protected].

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Author: Scott Berg has been sailing, racing and cruising for the past 50 years and has experience on a range of power and sailing vessels. Scott is the owner of Chardonnay Boatworks, a full-service marine repair and consulting company focusing on the repair and re-engineering of sail and motor yachts. He frequently lectures on marine electrical systems, electronics, and yacht systems and off shore sailing. Scott is a current member and past president of the Seven Seas Cruising Association (SSCA). He also holds a USCG 100T Masters license, an Amateur Extra Ham License, and currently lives on his 60’ Seaton Ketch, Chardonnay.

If you’ve found this article useful, you’ll find more similar information aimed directly at sailors/cruisers on the members-only portion of the SSCA website (www.ssca.org).