Why HF Radio Still Matters in Modern Defence Operations

What is HF radio, and why does it matter?

In defence operations, organisations need to communicate. They need to be able to send and receive orders, intelligence and situation reports quickly and securely; this can make all the difference between an operation succeeding or failing.

Militaries and governments often rely on SatCom and internet-based networks. These are fast and convenient but can be jammed or destroyed. Satellite links and ground-based infrastructure can be knocked out; this is where High Frequency (HF) radio plays an essential role and why NATO and militaries around the world still rely on it.

High Frequency (HF) radio, also known as shortwave broadcasting, operates on frequencies between 3 and 30 MHz. It enables long-distance communication by bouncing radio waves off the ionosphere (the electrically charged layer of the upper atmosphere), allowing signals to travel thousands of miles without cables or ground infrastructure in between.

At Isode, we make it possible to keep XMPP (Extensible Messaging and Presence Protocol), Email, MMHS (Military Messaging Handling), Command and Control (C2), and Web Browsing running over HF radio, so when the satellites fail, your communications don’t stop.

The evolution of HF radio: Automatic Link Establishment

Historically, using HF radio required skilled operators who knew how to tune frequencies and find a clear signal. This was a time-consuming and error-prone process, but that changed with the introduction of Automatic Link Establishment (ALE).

ALE automates the process of finding and connecting to the best available frequency in seconds. An ALE-enabled radio scans available frequencies, selects the best one for current conditions, and automatically completes a handshake with the receiving radio to establish a clean link.

New tools like Icon-Skywave, which is shipped as part of Icon-5066 (a modem-independent STANAG 5066 server which enables applications to work efficiently over HF modems and allows multiple applications to work simultaneously), enable HF propagation prediction through the ITU-R P.533 algorithm to forecast HF radio link performance as well as extend Icon-5066 capabilities to support ALE HF prediction, enabling systems to avoid frequencies that block communication at specific times.

Think of it like your phone automatically finding the strongest mobile signal, except it’s doing this across thousands of miles, without any cellular towers. It reduces dependence on specialist operators and speeds up the time to establish communications. While ALE improves one’s ability to use HF radio, it introduces new security challenges.

Why HF radio remains strategically essential

Despite advances in satellite and digital communications, HF radio still has advantages that no other technology currently replicates:

• Infrastructure independence: HF radio requires no external infrastructure between sender and receiver. It cannot be taken offline by targeting satellites or disabling ground networks.
• Resilience in challenging environments: When opponents block or destroy other communication channels, HF radio provides a reliable fallback that keeps command and control intact.
• Global reach: HF signals can travel intercontinental distances, making it ideal for operations in remote regions and at sea, where other communications are unavailable or unreliable.
• NATO standardisation: HF radio is embedded in NATO standards, ensuring interoperability across allied forces during joint and coalition operations.
• Low infrastructure cost: Deploying HF networks requires minimal infrastructure investment, making it a practical and cost-effective option for rapid deployment.

These characteristics show that HF radio is not merely a legacy system retained for historical reasons; it remains an active, mission-critical element of modern defence communications architecture.

Isode HF radio products

Isode offers a suite of HF radio software products, each designed to address a specific challenge in building and operating a modern military HF network.

Key products include:

• Icon-5066: a modem-independent STANAG 5066 server. It enables applications to work efficiently over HF modems/radios and allows multiple applications to work simultaneously.
• Icon-PEP: enables deployment of IP applications over an HF radio using the STANAG 5066 link layer. Icon-PEP supports IP packet switching and provides optimised support for TCP applications, such as web browsing and Command and Control (C2), using a Performance Enhancing Proxy (PEP).
• Red/Black: a web-based server that can provide management of different devices and servers. This is intended to complement, not replace, the primary device management tools. Red/black servers can operate in a pair to monitor and control devices across a secure boundary.
• Icon-Topo: A web interface that allows the operator to monitor and control the location of Mobile Units (MUs), scheduling their movements. This information is then used to control the configuration of applications and HF components to provide efficient communication as the MU traverses from one network access point to another.

Isode’s role in modern HF radio

Isode has spent years developing communications software for challenging environments. Our HF radio products are built on the understanding that HF networks must be not just functional but genuinely secure and interoperable with the implementation of standards like STANAG-5066, which operates over an HF modem and provides an interface for data applications to use and share an HF modem.

This can be seen through how we operate XMPP over HF Radio, provided through our M-Link products. HF networks typically have low bandwidth and high latency, which traditionally makes modern messaging protocols hard to deploy. However, Isode demonstrates that XMPP can be effectively adapted to these environments through optimisation techniques such as compression, traffic reduction, store-and-forward messaging, etc. Find out more here.

In addition to this, we extend HF capability beyond messaging to support full IP networking through Icon-PEP, enabling TAK (Tactical Assault Kit) and other Command and Control (C2) tools to run over HF Radio. Built on STANAG 5066 architecture, these C2 services are supported over HF Radio through the optimisation of TCP (Transmission Control Protocol) performance. You can learn more about this here.

Isode builds all its HF radio products on open NATO standards, primarily STANAG 5066, ensuring that an Isode-equipped system can communicate reliably with any other compliant system, regardless of underlying hardware. Isode products also integrate with secure messaging protocols, including XMPP and established military messaging standards such as STANAG 4406, ACP 127 and ACP 142, delivering end-to-end data protection across HF links from the application layer down.

Built for the demands of modern defence

HF radio has underpinned military communications for the better part of a century, and it remains as relevant today as ever, because nothing else does what it does. When satellites go dark and networks go down, HF is still there.

But the technology is only as capable as the software built around it. As operational demands grow and HF networks are asked to carry more applications, more users and more critical data, the need for modern, standards-based, purpose-built HF software has never been greater.

Isode’s HF radio software suite is designed to meet that challenge: delivering a secure, interoperable and operationally capable HF network that defence organisations can depend on, even in the most demanding environments.

Want to learn more? Explore our full range of HF radio products here.