• An omnidirectional broadband antenna and 5 meter Rolatube mast system weighs 11 pounds and can be set up and ready for transmit and receive in less than six minutes by one person.
     An omnidirectional broadband antenna and 5 meter Rolatube mast system weighs 11 pounds and can be set up and ready for transmit and receive in less than six minutes by one person.
  • Near vertical incidence skywave enables high frequency systems to communicate in mountainous terrain.
     Near vertical incidence skywave enables high frequency systems to communicate in mountainous terrain.

Bringing Communications Back Down to Earth

June 1, 2018
By Kurt Stephens and Bill Whittington


High frequency radios can bridge a beyond-line-of-sight gap during operations in contested environments.


With the development and fielding of satellite communications throughout the U.S. military, today’s warfighters rarely use high frequency communications within and between units. International events have increased interest in high frequency communications as an alternative to connecting via satellites on current and future battlefields. U.S. military units already own a large amount of the radio equipment suitable for employment at various levels of the battlefield and for humanitarian relief as a redundant means of beyond-line-of-sight communications.

Prior to the advent of tactical satellite communications (SATCOM), high frequency (HF) radios were the prevalent communications method. Beyond-line-of-sight communications of voice or data has always been a challenge for fixed station, mobile and deployed warfighters as well as first responders. As SATCOM developed, however, it quickly became the preferred long-distance backbone of most voice and data transmissions. As the use of HF seriously declined, equipment was left on the shelf and training all but halted.

The advantages of satellite communications are well known, but the disadvantages are rarely noted. In any communications scenario, a redundant capability to transmit and receive messages beyond line of sight is a necessity for leaders who insist on covering all avenues for success. In addition, today’s warfighter is being challenged with satellite-denied environments.

Because HF has been relegated to a lower priority tier of training and deployment, the skills necessary for its successful use gradually have eroded. Understanding signal propagation and techniques of antenna employment have faded, as has the functional use of existing HF radios. Simultaneously, the cadre of experienced HF instructors has retired and hasn’t been replaced, resulting in a lack of genuinely experienced personnel with a strong background in the use of high frequency equipment throughout the armed services.

When environmental elements such as weather or terrain eliminate or degrade SATCOM as an option, warfighters must be well trained to use other methods of communication. Redundancy is still a key to success when requirements exceed the capabilities of a single method of communications. The capability to continue to communicate despite limitations provides an advantage over less prepared operational forces or governments.

The number of satellites available to handle communication requirements limits the use of SATCOM. During conflicts, military satellites are augmented by commercial satellites, which are more vulnerable to interference. In a contested environment, the demand for SATCOM often exceeds the supply, so an access priority system is established.

This is not the case for HF communications methods, which do not require prioritizing; only additional or an alternate set of frequencies or networks to facilitate communications are needed. Proper use of HF will alleviate the demands on SATCOM and supplement connections. However, good spectrum management is still needed.

Relying heavily on SATCOM also poses other challenges. The majority of today’s satellites are commercially owned, and all satellites are susceptible to jamming, eavesdropping, hijacking, antisatellite weapons, electromagnetic pulses, cyber or infrastructure attacks, and spoofing by either friend or foe. As a result, warfighters must be prepared to put an HF network into operation quickly as a redundant, or in some cases primary, communications method.

In addition to electronic warfare and cyber attacks, rugged terrain, foliage and unpredictable weather patterns can inhibit signals, causing them to be intermittent or even blocked. HF can overcome difficult terrain issues by configuring an antenna system that utilizes the technique of near vertical incidence skywave (NVIS) propagation. This technique is specifically used for close communications within a range of up to approximately 600 miles, particularly in mountainous or jungle terrain. NVIS typically uses frequencies between 2 megahertz and 10 megahertz (MHz). Although weather and the environment can increase local noise levels on HF to varying degrees depending on the areas of the spectrum used, today’s radios have better noise filtering and error correction than past equipment.

For the military, HF has often been considered difficult and less than reliable. Many tactical commanders do not want to deal with what they perceive as a static-ridden, signal-fading, multiple-interference and sunspot-affected frequency band. However, technical advances have corrected many of these issues. For example, automated link establishment is one of the most significant improvements because it enables the radio to find the best signal path between stations for existing and changing conditions automatically. Vocoder technology, among other improvements, can virtually eliminate background noise.

U.S. government and military organizations own a tremendous amount of spectrum that falls into the high frequency range of 2 MHz to 30 MHz. Consequently, the newest wideband technologies can provide larger slices of bandwidth that can be used by HF radios at a much higher level of data throughput than previously available. Limited fielding of this capability is underway.

Other technical advances in high frequency communications include embedded encryption, advanced algorithms, frequency hopping and wideband operation. In addition, recent developments in engineering comprising silicon carbide and gallium nitride integrated circuit materials can handle more power in smaller packages and are more compatible over a wider frequency range, and improved antennas enable connection at lower power ratings, saving critical battery life.

Other advances include radios that operate in low probability of intercept/low probability of detection modes at very low power settings and often below the noise floor. HF equipment can be easily cross-banded to other radio platforms with plug-and-play devices. This includes HF to SATCOM to very high frequency, ultrahigh frequency, Wi-Fi, cellphones, landline and even two-way handheld radios. This capability extends the range of line-of-sight radio equipment to hundreds or thousands of miles, including beyond line of sight.

Position reporting via HF has been used for many years. In addition, the equipment can be used to interact with international allies, local or regional friendly forces, and first responders who have little or no SATCOM capabilities.

Advances in military antenna designs have improved communications and are adaptable to any mode of radio equipment. Antennas that comply with size, weight and performance requirements are available with lightweight rollup masts for easy transport as well as rapid setup and recovery by warfighters.

The path forward for the military to enhance operations in a contested environment or to rebuild a redundant method of beyond-line-of-sight communications is to capitalize on existing resources and reintroduce HF radio and antenna employment training into a working level of knowledge for the operators.

 

WO-4 Kurt Stephens, USCG (Ret.), is the CEO and technical director for White Wolf Systems, and Lt. Col. Bill Whittington, USA (Ret.), is the senior marketing director for the company.

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A very poignant and well directed article. Military and Federal radio communications has taken a strange course over the past recent decades, and this article is bringing the results of that into view. The significant result of which is the near complete loss of the science and art of HF radio communications. There are far too few legacy experts on HF radio remaining. Arguments end up claiming the number of remaining experts can be counted on the fingers of one hand. A very sad situation which should be quickly rectified by the Military, for they are the most prominent entity to suffer if this complete loss occurs.

To those persons who are ethical, responsible, and dedicated to the success of military communications, I send the message that they should gather themselves together and restore HF radio to a prominent position, for it will surely save them or their troops one day. And do not loose sight of its value as a handy alternative to the over-stretched condition of other radio venues. We have only to look at a recent drastic satellite failure to see the much maligned and obfuscated magnitude of presence HF radio still has: such as transoceanic flight air traffic control. It was only a short time ago when the ‘new’ satellite based CPDLC air traffic system failed for an extended time period (better part of the day), presenting a significant demonstration to the need for backup of such a critical function. In this case that backup was instantly provided by the often claimed ‘obsolete’ HF based transoceanic ATC.

Also as the article demonstrates one must maintain the need to not over look the affect which propagation can have on all radio communications. Many claim that HF suffers terribly from solar weather conditions. However, I counter that they are not properly nor completely informed on all affects solar weather has on radio communications. Radiation and particles emitted from the sun affects most radio communications in some manner. It overheats satellites, forcing them to be shut down until the danger diminishes, or they fail. Ionospheric changes cause aberrations to GPS navigation signals, scintillation of satellite signals, and extreme skip communications for HF radio. It can also cause radio blackouts, and anomalies on the electrical grids. Few realize that the satellite based communications has nearly as much “problems” with solar or ‘space’ weather as HF radio. It is true that these problems are in different realms of the radio signal propagation and in the hardware, however the satellite impediments remain real.

Transoceanic ATC is but one of the many instances where HF radio ‘saved the day’. Without that ATC HF system having been designed properly, supported, and manned by knowledgeable radio operators, it would be fair to project the existence of a situation of disaster over the ocean. That possibility being based solely upon the reliance upon a singular radio communications solution.

Being one of the few remaining legacy HF radiomen, I urge those remaining dedicated responsible persons using and managing radio communications to quickly reinstate HF into the radio communications suite of solutions. There has been far too much propaganda, obfuscation, and diversion toward other the preferred solutions, seemingly based upon other desires under the guise of mission success.

HF Radio has resoundingly demonstrated its dependability, flexibility, resilience, and capabilities since WWII. It unfortunately has fallen into a grey area from a lack of understanding, knowledge, and training. A sad and unfortunate situation for those needing radio communications in a harsh or undeveloped land area. I see a glimmer of those persons who are picking up an understanding of this situation and I look forward to their increased interest and establishment of HF radio and properly trained radio operators into their missions.

Being a legacy remnant of HF radio, I would be very happy to discuss HF radio with anyone who has interest in its use.

Thanks for the article. It is clear that the DOD should re-invest in HF communications. A balanced and integrated mix of assets, including HF sky wave, Satcom and possibly longwave (I.e., the legacy GWEN system), HF ground wave and even MBC is essential to be fully prepared in the event of nuclear conflict. HF is the obvious choice to pair with Satcom in a HANE environment.
For more information, see the decades old book “HF Communications: science & Technology” by john m. Goodman, JMG Associates

HF is still very much alive and well in the military. From US Army MARS to the US Army Recon School, folks are teaching HF and getting it back on track. Feel free to watch my new series on Military HF Radio. https://youtu.be/dZSLM7iFVMg

Civil Air Patrol has revitalized its HF capability, and the Air FOrce has taken notice. It will be interesting to see how the Air Force follows up on this capability in the future.

Some of the issues with satellites and solar particles involve actual impacts on sensitive components. Although these are ionizing particles, the actions on satellites are different in nature from the ionization changes seen to the E and F layers of the ionospherewhen acted upon by magnetic and particulate fluxes, and generalizing about the two can lead to problems. Similarly, the phenomena affecting GPS by scintillation are not exactly what causes changes to the F1 and F2 layers that elicit different refractive indices.

As organizations like USAF revisit HF, they will have a lot of learning to do. Having both CAP and AFMARS available to help explain how things work will help, although even among the ranks of experienced ham operators, I fear the actual knowledge-base of ionospheric propagation remains pretty thin.

I beg to differ. While I've noticed a decrease in ham HF usage over the 50 years I've been playing radio, there is still plenty of activity, and dozens of knowledgeable discussions. An ad in the American Radio Relay League's publication, QST, might be a worthwhile recruiting investment

Ted, a big part of the problem is that what's "known" about the ionosphere in our hobby is often based on more subjective assessment than objective evidence. There are good research programs out there, and indeed, one has roots in Amateur Radoi: HamSci, the same folks that brought you the Solar Eclipse QSO Party. That said, most of the long-term operators... and I've been around about as long as you mention... have at best an instinctive rather than fact-based understanding of what to use, when and for what purposes.

Then again, I think getting an ad in QST is not a losing proposition, and perhaps getting an article on what's happening might also be worthwhile.

Gerry N5JXS

I had a big lightning strike a 100m from my HF antenna that was plugged in to an ICOM 7200 hf radio and the radio suffered no damage at all.
It took the roof off the neighbours house And blew the transformers up.
Maybe these radios are more resilient than we think.

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