MF/HF Radios and Radiotelex – Integration, Testing, and Modern Technologies

Introduction

Safety at sea is a priority for every vessel, regardless of its size or purpose. Communication systems such as MF/HF radios and radiotelex play a crucial role in ensuring uninterrupted connectivity on waters worldwide. While modern satellite systems are becoming increasingly dominant, traditional technologies remain an indispensable part of equipment, especially on merchant ships and in areas where satellite infrastructure may be limited. This article discusses both the operation and testing of these systems and their relevance in modern navigation.

MF/HF Radios – How They Work and Why They Matter

MF/HF radios operate using medium-frequency (MF: 1.6–4 MHz) and high-frequency (HF: 4–27.5 MHz) radio waves. A key feature of these systems is their ability to provide communication across different maritime zones:

1. Medium-Frequency Communication (MF): In Zone A2, which covers up to 150 nautical miles from the coast, MF radios use ground waves. This allows ships to communicate directly with other vessels and coastal centers. It is particularly vital for vessels operating in coastal regions with readily accessible shore stations.
2. Long-Range Communication (HF): In Zones A3 and A4, HF waves reflected off the ionosphere enable communication over distances of thousands of kilometers. This is indispensable in oceanic navigation, where other means of communication may be unavailable.

Changes in Transmitter Power Standards:
Until recently, 500W or higher-powered radios were the standard. These devices offered unmatched range and the ability to overcome atmospheric interference. However, more ships now use 150W radios. While their range may be smaller, they are more energy-efficient, compact, and easier to operate, addressing the needs of modern shipping, which demands increasingly advanced yet efficient solutions.

Radiotelex – Digital Text Transmission Under Challenging Conditions

Radiotelex (NBDP – Narrow Band Direct Printing) is a system that enables text message transmission over long distances, even under radio interference conditions. This solution is especially valued in navigation, where communication reliability is crucial. Radiotelex operates in two main modes:

• ARQ (Automatic Repeat Request): A two-way system where each message must be acknowledged by the recipient, ensuring that the communication was successfully received.
• FEC (Forward Error Correction): A one-way mode where each message is sent twice, allowing correction of potential errors during reception. This is particularly important for transmitting weather forecasts or navigational warnings.

Radiotelex is often used in combination with MF/HF radios, which provide the transmission infrastructure. For example, in the event of a DSC alarm, radiotelex enables the transmission of detailed instructions in text form, complementing voice communication.

Modern Trends – Satellite Systems Surpassing Traditional Technologies

With advancing technology, MF/HF and radiotelex systems are being supplanted by modern satellite solutions such as the LT-3100S. Satellite systems offer global coverage, ease of use, and data transmission capabilities, making them increasingly attractive to shipowners. As previously discussed on our blog, LT-3100: A Modern and Comprehensive (GMDSS) Satellite Communication Solution for Maritime Use, the LT-3100S stands out with:

• Global coverage: No limitations regarding operational areas.
• Versatility: Capability to send text messages, make voice calls, and transmit data.
• Reliability: Uninterrupted performance regardless of weather conditions.

Despite the advantages of satellite systems, MF/HF and radiotelex technologies remain indispensable in emergencies where reliability and quick access to rescue frequencies are crucial.

Testing MF/HF and Radiotelex Systems

Regular equipment testing is not only a regulatory requirement but also a safety guarantee. Here’s how to properly conduct tests:

Testing Radiotelex

1. Preparing the System:

• Check the correctness of terminal and radio connections.
• Enter the Answerback Code and ship ID.

1. Conducting an ARQ Test:

• Select ARQ mode on the terminal.
• Send a test message to another station. A successful test is confirmed by receiving the message: “The quick brown fox jumps over the lazy dog”, verifying correct transmission.

1. Conducting an FEC Test:

• Set FEC mode and send a test message to multiple recipients. Verify the correctness of the received messages.

1. Logging Results:

• Record test results in the radio logbook (along with printouts), in compliance with SOLAS requirements.

Testing MF/HF Radios

• Perform an internal DSC (Digital Selective Calling) system test.
• Conduct a DSC test call on MF (2187.5 kHz) and HF frequencies with other ships or shore stations. If you have internet access, use the WebSDR platform to listen to your broadcast in real-time.

Safety:

High voltages are present during transmission. Exercise extreme caution near the antenna line.