Single-Sideband Radios Endure

There's still a place in the nav station for a long-range radio.
Typical single-sideband transceiver installation Illustration by Tim Barker

Cold-hearted is the sailor who doesn’t daydream of slipping the lines and setting sail to parts unknown. Troubles arise for many of us, however, when we try reconciling this dream with the connectivity demands of modern-day living, not to mention the desire for weather information while at sea and the ability to reach out in case of an emergency. True, satellite-communication options exist for the bluewater sailor — at a price — but some prefer instead to rely on technology that’s been in use for the better part of the past century: high-frequency radio communication. Once thought of as a hard-to-master black art, communicating by single-sideband radio is greatly simplified these days, thanks to improved antennas and digital signal processing that takes much of the guesswork out of frequency selection, which is key to successful radio transmissions. Add a Pactor modem to the mix and your radio becomes a data hub capable of sending and receiving email and weather forecasts anywhere on the globe. In 1915, John Renshaw Carson applied for the first U.S. patent for single-sideband modulation, a technology that dramatically increases the efficiency of a radio’s amplifier by only broadcasting one half, or the sideband, of a traditional AM radio signal. AM radios, by contrast, combine a specific radio frequency (the carrier wave) with a broadcast signal that includes the message or data being communicated. By broadcasting only the sideband portion of the signal, SSB radios are able to use their amplification power more efficiently, and they can harness the phenomenon of so-called skip, or sky wave, propagation, where radio waves are reflected or refracted between Earth’s electrically charged ionosphere and the ground to deliver significantly ­longer-range transmissions than an AM radio or the line-of-sight VHF radios often found on sailboats.

Not surprisingly, the military seized on the ­single-sideband technology, and improved radio sets were developed quickly. Following World War II, these long-­distance communication devices became popular with radio enthusiasts and cruising sailors, eventually giving rise to a culture of cruising nets that provide mariners increased safety while at sea and a virtual community of fellow cruisers.

While SSB radios require more user knowledge than other contemporary communications options, such as a satphone or transponder like those available from Garmin, they provide a global communications network that allows simultaneous communications with multiple parties, while also enabling users to send and receive email and low-­bandwidth data, call individual phone lines, issue two-way emergency broadcasts and participate in the aforementioned radio nets. Best yet, airtime is free. Here, then, is a look at how SSB radios work and the benefits they provide.


Skip It

As mentioned, SSB radios use sky-wave propagation to communicate over long distances, provided that their users select the correct frequency. When a signal is transmitted, it travels diagonally toward the ionosphere before reflecting back to Earth, where it’s either received or refracted back toward the ionosphere. Sky waves can be received each time they reach Earth. However, some of their signal strength dissipates with each bounce (called absorption). Because of this, SSB operators use distance to determine their ideal broadcasting frequency based on their sky wave’s predictable first bounce. Choose a frequency that’s too high and the signal will skip over its intended target; pick a frequency that’s too low and the signal won’t reach its mark. Here, a ballpark rule is that a 2 MHz signal will make its first bounce 200 to 400 miles from your position; a 4 MHz signal will travel 400 to 600 miles; a 6 MHz signal 600 to 1,200 miles; and a 12 MHz signal 1,200 to 2,400 miles before hitting Earth. The performance of signals at the upper end of a radio’s frequency range — 26 MHz and above — becomes unpredictable during certain solar periods.

Marine SSB radios operate on the frequency bands between 2 and 26 MHz. Given the wide swath of frequencies involved, SSB radios are set up to operate on channels that are programmable (more on that in a minute). For instance, 4,146 kHz might equate to Channel 77 on an Icom radio. Unlike VHFs, for which Channel 16 is always Channel 16, SSB radio channels (but not their frequencies) depend on the radio’s make and model, and are also user-­programmable, meaning Channel 77 on your radio likely doesn’t yield the same frequency as Channel 77 on your buddy’s system.

Radio install
(Above, from left) An antenna tuner, a KISS-SSB counterpoise and a GAM/McKim Split Lead antenna that snaps onto, or can slide over, a backstay. Photos courtesy of the manufacturers

SSB radios can broadcast and receive signals on 1,000-plus channels. However, says Steven Bowden, the owner of SeaTech Systems and a nationally recognized SSB expert, only 100 or so will likely yield good reception simultaneously.

For example, the U.S. Coast Guard monitors certain SSB ship channels (including 4,135 kHz, 6,200 kHz, 8,240 kHz, 12,242 kHz and 16,432 kHz) for emergency calls, and these same channels are also used to broadcast regularly scheduled marine-weather forecasts. The Coast Guard and the Federal Communications Commission control these radio frequencies, and the National Weather Service supplies the Coast Guard with its weather ­information for broadcast.

SSB radio signals can be affected by any number of externalities:

  • The state of the ionosphere (how high and how dense it is)
  • The angle of radiation (its broadcast angle)
  • Time of day (the ionosphere rises during the day, allowing for longer transmission range)
  • Season (the ionosphere is higher and denser during the summer)
  • Sunspot activity (more activity equates to longer transmission range)
  • Radio frequency, or RF, interference created by other onboard electrical devices
  • While some of these externalities are unavoidable, users can reduce onboard RF interference by ­powering-down devices and systems such as computers, fluorescent lights, and engines and motors when using an SSB radio.

SSB Nuts and Bolts

A common SSB radio installation includes the radio, an antenna and a counterpoise, also known as a ground plane (and not to be confused with the ground wire in a DC electrical system). Additionally, SSB users typically add an optional automatic antenna tuner and a Pactor radio modem, the former of which simplifies operations while the latter allows for data transmission via SSB frequencies. While radios, tuners and modems are off-the-shelf items, antennas and counterpoise installations vary considerably.

An antenna must be sized according to the lowest frequency that a user plans to employ; the lower the frequency, the longer an antenna needs to be. For example, if someone wants to use frequencies of 4 MHz and up, they could opt for an antenna that’s 9 feet 10 inches or longer; to transmit on 2 MHz requires an antenna that’s at least 23 feet long.


“Shakespeare makes a ­popular 17-foot SSB antenna, but it might lose some frequencies,” says Bowden. In general, he adds, the longer the antenna, the better.

To maximize antenna length and quality, some boats incorporate an antenna in the backstay with a set of insulators that dictate the antenna’s length. Bowden suggests that budget-minded cruisers instead consider a GAM/McKim Split Lead antenna, which is typically attached to the backstay.

Transmitter antennas, say, at a radio station, take advantage of the proximity of the ground, which is turned into a counterpoise, usually via metal that’s driven into the ground. The counterpoise “counters” the broadcast signal, forcing it into space. To replicate this on board a vessel, mariners typically attach an SSB’s ground wire to a bronze block on the outside of the hull.

Another approach is to incorporate a copper mesh that’s laminated into the hull, or to tie in a boat’s metal water tanks, seacocks or engine block, though these latter solutions aren’t terribly effective and must not also be connected to the vessel’s grounding system, lest a keyed microphone interfere with other electronics. If you’re adding an SSB to a boat without a built-in counterpoise, Bowden suggests that RadioTeck’s KISS-SSB can be a cost-effective solution.

Given the complexity of SSB hardware, Bowden suggests DIYers would be wise to have their radios and related equipment professionally installed, especially if the backstay will be moonlighting as an antenna.

As of this writing, Icom’s M802 ($3,420) is the only SSB transceiver that’s in ­production. The M802 boasts 150 watts of transmitting power, a frequency range of 0.5 MHz to 29.99 MHz, emergency digital selective calling (DSC), 160 user-programmable channels and an interface that’s user-friendly enough for mere-mortal mariners to negotiate, given enough time and — advises Bowden — Icom’s AT-140 automatic antenna tuner ($710). The M802 was originally introduced in 2002 but removed from the market in 2013 due to an unfulfilled FCC requirement, for which Icom received a waiver in fall 2017. According to David McLain, Icom’s national marine sales manager, the radio was reintroduced thanks to “the demand from the cruising market. They rely on SSB for offshore communications.”

Icom’s IC-M802
Icom’s IC-M802 is the only marine SSB radio that’s now in production. Paired with a Pactor modem, it allows users to send and receive emails and download weather files at sea. Photos courtesy of the manufacturer

Unlike SSB radios of yore, Icom’s M802 features digital signal processing, which, says McLain, simplifies and expedites sending and receiving email, provided one has a networked Pactor modem and an active contract with a high frequency (HF) email provider such as SailMail or Winlink. Factor in an AT-140 automatic tuner and the result is a radio that’s much easier to operate compared to vintage models. However, admits McLain, “they’re still a little confusing to use.” Because of this, Bowden and McLain encourage skippers to read up on the topic (see “Additional SSB Resources,” below) and gain experience before heading offshore.

Learning curve aside, SSB radios deliver some critical and difficult-to-replace benefits. For starters, they enable one-on-one communications (albeit on an open frequency) and also allow multiple parties to simultaneously listen to a communication issued by an individual user (just like VHF). Additionally, by first hailing a public correspondence station (for example, WLO in Mobile, Alabama, or FLB near Seattle) that facilitates the connection, SSB users can make traditional phone calls. An optional Pactor modem allows users to send and receive emails and download weather GRIB files, and users can configure their modems for SMS messaging over SSB frequencies.

Besides staying in touch with other cruisers, an SSB radio is of value in emergencies, Bowden notes. Not only can a broadcast alert other mariners of your predicament, it can put a sailor in direct contact with rescue personnel. For instance, when an EPIRB is activated, the rescuing authority’s job is to save lives, often at the expense of the vessel. With SSB communications, says Bowden, a distressed ­mariner could instead call the U.S. Coast Guard and advise them of the situation so appropriate emergency equipment could be delivered and the vessel saved.

Unlike testing-intensive ham-radio licenses, SSB users only need a valid ship station license and a Restricted Radiotelephone Operator’s permit to transmit on SSB marine frequencies. However, any SSB user can listen to the ham-radio frequencies.

Critically, “There are no rules if someone’s life is in danger — that’s the exception,” says Bowden about unlicensed users transmitting on ham frequencies. “You can use any frequency and somebody will be listening.”

Serious business aside, operators can also use their SSB radio to receive AM, FM and shortwave radio stations for news, sports, music and other broadcast entertainment.

While SSB users can expect a certain learning curve — and while newer technologies, including satellite communications, are becoming cheaper and offer more widespread coverage — these powerful radios still have their place aboard serious bluewater cruising boats. They deliver free single- or multiparty communications; allow for email, weather, entertainment and access to cruisers nets; and they satisfy most race and rally requirements for global communications.

Additional SSB Resources

Capt. Marti’s Idi-Yachts Books:
Chris Parker’s Marine Weather Center:
Cruisers Forum:
Digital Selective Calling:
Federal Communications Commission:
Global Maritime Distress and Safety System:
Gordon West Radio School:
HF Nets:
Hurricane Watch Net:
Lee Chesneau’s Marine Weather:
Maritime Mobile Service Network:
NOAA Marine Radiofax Charts:
National Association for Amateur Radio:
Pam Wall Cruising and Sailing Consultant:
SailMail Association:
SeaTech Systems:
Seven Seas Cruising Association:
Terry Sparks Radio Books:
Two Can Sail:
Waterway Radio:
WLO (Mobile, Alabama):
World Cruising Club: