Introduction

Understanding the principles and operation of medium and high frequency radio (MF/HF-SSB) can be complex and extensive, but for the average maritime user, a basic understanding is essential for effective communication. In this article, we aim to provide you with some fundamental knowledge, although it’s important to note that we won’t cover every possible factor or situation.

What is MF/HF-SSB?

The MF/HF-SSB marine radio is a combined transmitter and receiver, similar to your VHF radio. The key difference lies in the frequency ranges they operate in. Typically, marine MF/HF-SSB radios function within the range of 1.6 MHz to 30 MHz. The crucial concept to grasp here is that these radios allow operators to select frequencies based on atmospheric conditions to establish communications over varying distances.

Unlike VHF, which primarily operates on a line-of-sight basis, MF/HF radios can refract their signals within the atmosphere, providing increased range. This feature is crucial for long-distance ship-to-ship or ship-to-shore communications.

Why do you need an HF radio?

The primary reason for using an HF radio is safety, but even for routine long-distance communications, it becomes a vital consideration. When your maritime activities take you further offshore, such as fishing in canyons or venturing from the mainland to offshore islands, you’ll quickly realize that your trusty VHF radio is no longer sufficient.

Once the distances exceed approximately 30 nautical miles (depending on antenna heights), the VHF marine radio becomes inadequate for both regular and emergency communications. To maintain this lifeline of communication, you will need to use an MF/HF radio or a satellite communications system.

The rapid advancements in electronics over the past few decades, similar to those witnessed in personal computers, have also benefited the manufacturing of radio communications equipment. Today, even average boat owners can access HF worldwide communications systems that would have been envied by large ships in the past.

In addition to long-range communication capabilities, HF-SSB radio sets can be easily adapted to provide users with various other services. Email, teletype, NAVTEX, and weather facsimile are among the many functions that can be accessed with the help of a computer, appropriate software, and a modem. Moreover, many newer marine HF-SSB radios can be “Unlocked,” granting access to amateur radio frequencies for boaters who hold an amateur radio license.

How far can you communicate?

Unlike marine VHF radios that operate in the frequency range of 150-160 MHz, MF/HF radios utilize lower frequencies ranging from 1.6 to 30 MHz. These lower frequencies play a crucial role in enabling HF radios to communicate over much longer distances. In fact, under favorable conditions, worldwide communication is possible. Due to this and the relatively low cost involved, HF-SSB is incredibly popular among blue water passagemakers and long-distance or world cruisers.

The distance over which reliable communication is feasible depends on several factors. Here are a few of the most common ones:

1. Time of day
2. Season of the year
3. Frequency in use

Many of these factors are closely linked to the sun’s influence on the Earth’s atmosphere. The sun’s impact on HF communication is likely the single most important factor, leading us to the next topic: “Propagation.”

Propagation

To effectively communicate and harness the full potential of your HF radio, an operator must possess a basic understanding of radio wave propagation.

“Propagation” refers to the refraction and reflection of radio waves by different layers of the ionosphere. There are three types of propagation relevant to HF radio, which occur simultaneously: Ground Waves, Direct Waves, and Sky Waves. In this article, we’ll focus on two types that are particularly important for mariners:

1. “Ground Wave”: This type of propagation follows the curvature of the Earth’s surface. Ground wave propagation is effective at lower frequencies and is rarely viable above the 3 MHz band. It is ideal for relatively short distances during the daytime, typically ranging from 100 to 200 nautical miles, occasionally extending up to 400 nautical miles at night.
2. “Sky Wave”: Sky wave propagation occurs when the radio signal refracts through a specific layer of the ionosphere and returns to Earth. Due to this refraction, longer distances can be achieved, often spanning thousands of miles during the day and many thousands of miles at night.

Radio wave propagation often poses challenges for new HF radio operators. Many are perplexed when they can’t communicate with the Coast Guard, located just 250 nautical miles away, even when using a frequency capable of reaching distances of 4000 nautical miles. The simple explanation is that with higher frequencies required for long-range communications, the ground wave may not reach the intended station, and the sky wave might pass right over it.

The illustration below provides a visualization of this phenomenon. Any station within the “skip zone” will likely never hear your broadcast.

Choosing the right frequency

The basic rule for using HF radio is to determine the approximate distance you want to communicate. Once you know the distance, selecting an appropriate frequency becomes a straightforward task.

Here are some general guidelines for frequency selection:

1. The higher the sun is above the horizon, the higher the frequency required for communication.
2. For the same frequency, communication is usually possible over greater distances at night compared to daytime.
3. Winter generally allows for better communication distances than summer.
4. Higher frequencies generally enable longer-distance communication.

While these guidelines are helpful, it’s important to remember that they are not fixed rules. Several computer programs and applications are available on the market to assist in selecting the right frequency for communication. Some programs even consider current solar phenomena to improve the accuracy of their calculations. However, for the average marine HF radio user, these tools are not necessary.

Various tables, like the one provided below, offer starting points for selecting the appropriate frequency for specific communication distances. These tables should serve as reasonable references for choosing the correct frequency.

Marine MF/HF-SSB Sky Wave Propagation

MF/HF Frequency Band	Day	Night
2 MHz	Ground wave coverage only.	Up to 400 nautical miles.
4 MHz	Up to 400 nautical miles.	Up to 600 nautical miles.
6 MHz	Up to 600 nautical miles.	Up to 1200 nautical miles.
8 MHz	Up to 800 nautical miles.	Up to 1600 nautical miles.
12 MHz	Up to 1200 nautical miles.	Up to 2400 nautical miles.
16 MHz	Up to 1600 nautical miles.	Up to 3200 nautical miles.
22 MHz	Up to 2200 nautical miles.	Up to 4000+ nautical miles.
26 MHz	Often unpredictable or unusable.

Remember, the sky wave ranges shown above are approximate and can vary significantly due to atmospheric conditions. Unlike VHF, the HF ranges listed do not imply direct communication to anyone within that range. Instead, they indicate the approximate ranges within which communication is possible.

For example, if you are trying to contact a shore station or ship station located approximately 1500 nautical miles away at 1400 local time, a suitable starting frequency might be within the 16 MHz band. Applying the rule of multiplying the frequency band (16 MHz) by 100, you get an average range of 1600 nautical miles. You can then try frequencies above or below that band to check for improved communications.

Simplex / Duplex / USB / LSB / A3 – What?

Let’s briefly explain some of the terminologies you will encounter when using a marine HF-SSB radio.

1. “ITU Channels”: The International Telecommunications Union has established a standardized list of paired frequencies for transmitting and receiving, assigning them channel designators. These ITU Channels utilize the same frequencies worldwide, similar to VHF.
2. “Simplex”: Simplex refers to using the same frequency for both transmission and reception. For example, transmitting and receiving on 2182.0 kHz.
3. “Duplex”: Duplex involves transmitting on one frequency (e.g., 8195.0 kHz) and receiving on a completely different frequency (e.g., 8719.0 kHz). This particular frequency pairing is known as “ITU Channel 801.”

In general, ship-to-ship communications use simplex frequencies where both transmit and receive frequencies are the same. Duplex frequencies, on the other hand, are intended for ship-to-shore communication, although simplex frequencies can also serve this purpose.

Regarding Upper Sideband (USB), Lower Sideband (LSB), Amplitude Modulation (AM), and the A3J/A3A/A3H emission settings on your HF radio, it is practical to leave them set to “USB” and “A3J” for voice communications using marine HF-SSB. Most marine HF-SSB radios come pre-programmed with a wide selection of channels for immediate use. While some channels can be re-programmed, distress frequencies, both voice and DSC, are usually non-modifiable.

Licensing

Due to the complexity of operating HF/SSB radios compared to typical VHF marine radios, most countries, including the U.S., require vessels equipped with MF/HF SSB radios to obtain a station license, and operators must also be licensed. For more details, refer to our Ship Station Licensing and Radio Operator Licensing pages.

It is highly recommended that HF-SSB radio operators receive some form of training. Whether through formal instruction or self-guided learning, a solid understanding of HF radio procedures is crucial for efficient operation of your MF/HF-Single Sideband Radio.