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High-Frequency Radio Basics

HF radios are essential for safety, weather, entertainment, and communications with home.
Offshore cruisers should not leave home without a high-frequency radio.  Because they are capable of worldwide communications, these radios open a large safety net for sailors who travel out of the range of coastal VHF and cell phone communications.  HF radios not only provide a method of obtaining help in the event of an emergency, but they can receive a wide array of weather information including weather fax and voice weather broadcasts.

Most cruising sailors use their HF radios for long-distance voice communications to keep track of friends, family, and their cruising buddies scattered across the globe. Some types also permit the conduct of business and almost all transceivers allow reception of a tremendous variety of entertainment broadcasts and news from around the world. Nets of cruising sailors meet on a regular schedule each day to share information on weather, sailing routes, and information of interest to cruisers. With recent advances in technology, HF radio has also become a method for e-mail communications and telephone.

With all these advantages, it’s no wonder that cruisers undertaking their first offshore ventures often have numerous questions about HF radios. Most of the confusion over the choices is due to there being two different types of HF radios in wide use—every cruiser will have to decide whether to use HAM radio or Marine Single Sideband (SSB). Each has its own special set of advantages and disadvantages—so much so that some cruisers have both types on board.

HAM and SSB radios use the same basic frequency ranges from two MHz up to 22 MHz, with HAMs allotted frequencies extending on up to nearly 30 MHz. The actual frequencies, however, are different, and by FCC regulation, many radios are limited to only the legal bands for which they were designated. While some cruisers know how to "open up" their radio’s transmitting capabilities so that a HAM radio becomes able to transmit on Marine SSB frequencies, this practice can result in stiff fines, confiscation of the radio equipment, and permanent loss of the radio license. The FCC has recently "type certified" radios capable of transmitting on both HAM and SSB frequencies, and if getting a HAM license in the future is a possibility, buying a combination HAM/SSB radio is a wise move. You will not be legally able to use the HAM portion until you obtain the proper license (except in an emergency), but it will save purchasing another radio in the future.

Both HAM and SSB transmissions are carried by one half of an Amplitude Modulation (AM) wave. We are all familiar with many of the properties of double sideband AM radio broadcasters, where stations a continent away can be heard at night but only travel a few miles during the day. Single sideband transmission is defined, simply, as the suppression of one half of the carrier frequency, and so each transmission is completed either on the "lower sideband (LSB)" or "upper sideband (USB)." All Marine Single Sideband transmissions, including weather fax and voice transmission are conducted on the USB—HAM transmissions below 10MHz are on the LSB while those above 10MHz are on the USB. As you can see, the term Marine Single Sideband is somewhat of an unfortunate misnomer since HAM operators are also transmitting in a single sideband format.

It is critical that every boat going out of the range of VHF or other coastal sources of information on weather or other hazards have at least a modest HF receiver. A simple HF receiver allows every cruiser to listen to the active cruising world but without the ability to transmit. When considering the purchase of a HF receiver, it is important that you understand the difference between the inexpensive types that receive only AM (double sideband) broadcasts and a model capable of single sideband reception. Look for a model that has a sideband switch or BFO (Beat Frequency Oscillator) that allows you to switch from USB to LSB. Radios that receive full AM (double sideband) will only garble both HAM and SSB transmissions, making them unintelligible.

MARINE SINGLE SIDEBAND (SSB)    The equipment required for a SSB radio station is the radio, which depending on features will cost in the $1,500 to $3,000 range, a tuner, an antenna, and a ground plane. SSB radios come with or without automatic internal tuners but, whether internal or on optional separate unit, the automatic variety makes the radio easier to operate, especially for novices. If you have a good background in electrical installations and a complete toolbox, you can probably install a SSB system yourself, but professional installation is recommended for the most effective operation. Most sailors run the antenna the length of the backstay with insulators at either end, keeping the lower one just above the crew’s reach—a live transmitting wire antenna has been known to cause burns. A good antenna, ground plane, radio, and tuner will provide worldwide communications on a wide frequency range.


  • Of the two communications systems, HAM and Marine SSB, SSB is the easiest to obtain licensing. The FCC requires only a station license. A form can be obtained from the store where the equipment is purchased, filled out, and mailed to the FCC.
  • There are no tests and the use protocol is basically the same as for VHF radios.
  • On certain Marine SSB frequencies, limited business can be conducted whereas with HAM radio, business over the airwaves is not permitted.
  • Commercial radiotelephone calls are permitted.
  • Weather and information nets are numerous and easily available in all parts of the world.
  • SSBs can transmit and receive anywhere in the world without reciprocal licensing requirements.
  • The SSB radios are designed and built for the marine environment and are less affected by corrosion and salt air in the delicate electronics.


A complete array of HF radios keeps you in worldwide contact.
  • Marine SSB is more limited in usable frequencies than HAM radio.
  • Phone patches home will cost money.
  • Ship-to-ship frequencies available for "chat" are limited.
  • The radio and tuner equipment are generally more expensive than a comparable HAM radio.

HAM RADIO    Amateur radio operators are generally called HAMs, and they have been instrumental in experimenting with and advancing radio technology for over a century. Again, the term "amateur radio operator" is somewhat misleading as SSB operators are also amateurs in the sense that their transmissions are meant to be received only by another amateur radio operator and are not for public broadcast. The main differences between HAM and SSB operators are in the licensing requirements, the number of frequencies they have available, and the type of transmissions allowed.

Many sailors consider the HAM licensing requirements a disadvantage, but the HAMs regard them as an opportunity to learn and understand more about the operation of the radio. There used to be five levels of HAM licenses—Novice, Technician, General, Advanced, and Extra—each opening more frequencies for those who attained the level of competency. Each level used to have both written and Morse code exams at increasing levels of difficulty—five words per minute for Novice and Tech, 13 wpm for General and Advanced, a professional-level 21 wpm for Extra. But these levels have been reduced to only three—Technician, General, and Extra. And the Morse code requirements have been reduced to no requirement at the Technician level and only five wpm for the General Class and Extra. This has made obtaining a HAM license much easier for most people. The code requirement has also been totally eliminated for folks with hearing impairments, opening more opportunities for them to enjoy HAM radio.

As with the SSB setup, a HAM rig consists of the radio, a tuner with SWR meter (if the tuner is not built into the radio), antenna with insulators, and a ground plane. Once again, unless you’re handy with electronics, antennas, and ground issues, a professional installer is recommended.


  • Access to more frequencies, depending on the license, which equates to greater transmission distances and less crowded areas of the airwaves.
  • HAMs are able to discuss any noncommercial topic they want for as long as they want.
  • Many 24-hour-a-day nets are operated by volunteers who will relay messages and are always listening for distress calls.
  • The HAM radio, with or without a built-in tuner, is usually less expensive than a SSB unit.
  • Packet radio provides e-mail communications between HAMS.
  • Telephone patches are free, no High Seas Operator is required.
  • Slow Scan TV (SSTV) provides the availability to send pictures anywhere with software and a laptop.
  • Satellite communications are available for text e-mail.


  • Transmissions that are business oriented, or are pecuniary in nature, are not permitted.
  • Reciprocal licenses are required for each country transmissions will originate from.
  • HAM radios are generally built for use in a home or land-based vehicle, and many do not hold up well to the marine environment.

Combination HAM/SSBs are compact and made for the marine environment.

Each system has its own unique qualities and the obvious choice would be to have one radio with both HAM and SSB capabilities along with the proper licenses if study time and the budget permit.

But remember, without the HAM license you cannot transmit on the HAM frequencies. The owner’s manual for your radio will tell you which frequencies to use for HAM or SSB transmissions. There are also guides available from the FCC, the US Coast Guard, and the American Radio Relay League (AARL).

Terms and Frequencies

These are terms that will help you understand the basics of high-frequency radio operation so that you can read the literature and owner's manuals:

  • Amateur Bands are the frequencies between 1.8MHz to 29.7 MHz set aside for amateur radio operators, better known as HAMS.
  • Amplitude is the height of a radio or sound wave loudness
  • Amplitude Modulation is the addition of information to a RF carrier by increasing and decreasing amplitude. These are low efficiency types of radio transmissions, which are used for AM radio stations with 100 percent carrier inserted.
  • Carrier is an unmodulated RF signal.
  • Duplex frequencies are available in which ship stations transmit on one frequency while shore stations transmit on another.
  • Frequency is the number of polarity alternations per second measured in Hertz, whereas kHz equals a thousand Hertz and MHz equals a million Hertz.
  • Hertz (Hz) is a measure of frequency, which is one cycle per second.
  • HF is High Frequency, which are frequencies in the 3 to 30 MHz ranges.
  • LSB is the Lower Sideband of a carrier frequency.
  • Modulation is the varying of amplitude, frequency, or phase of a carrier signal.
  • Propagation is the different characteristics of radio frequency transmissions, in which the usable distance of a transmission is related to the frequency and time of day.
  • RF is any frequency, referred to as radio frequency, higher than humans are capable of hearing.
  • Simplex frequencies are for stations to transmit and receive on the same frequencies.
  • Transceiver is equipment that transmits and receives.
  • USB is Upper Sideband of a carrier frequency.

Also important to know is the somewhat confusing relationship between meters and MHz when HF radio operators refer to, for instance, the 10-meter band. Below are the basic bands available not including the higher frequencies and the centimeter bands available.

  • 1.25 meters = 222.00 to 225.00 MHz
  • 2-meters = 144.0 to 148.0 MHz
  • 6-meters = 50.0 to 54.0 MHz
  • 10-meters = 28.0 to 29.7 MHz
  • 12-meters = 24.890 to 24.990 MHz
  • 15-meters = 21.0 to 21.450 MHz
  • 17-meters = 18.068 to 18.168 MHz
  • 20-meters = 14.0 to 14.350 MHz
  • 30-meters = 10.100 to 10.150 MHz
  • 40-meters = 7 to 7.3 MHz
  • 80-meters = 3.5 to 4.0 MHz
  • 160-meters = 1.8 to 2.0 MHz

Suggested Reading

  1. Choosing and Installing a SSB Radio by Sue & Larry
  2. Setting Up HAM Antennas by Sue & Larry
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