commercial HF radio

According to a traditional system of classification, "high frequency" or HF refers to the radio spectrum between 3 and 30 MHz. The label now seems anachronistic, as HF is among the lowest ranges of radio frequencies that see regular use. This setting of the goalposts in the early days of radio technology means that modern communications standards like 5G are pushing major applications into the EHF or "extremely high frequency" band. The frontiers of basic radio technology now lie in the terahertz range, where the demarcation between radio waves and light is blurred and the known techniques for both only partially apply. HF, by contrast, is ancient technology. HF emissions can be generated by simple, brute-force means. Ironically, this makes HF a bit difficult: the incredible miniaturization and energy efficiency of modern electronics makes HF radio hard to receive and transmit in a reasonable footprint, one of several reasons that HF radio sees little consumer use.

Let's briefly consider the propagation characteristics of the HF band, which are its most remarkable property. HF frequencies have long enough wavelengths that they can reflect and refract in the earth's atmosphere. Somewhat like the skin effect observed with AC electricity or surface tension in liquids, HF emissions have a tendency to bend their path to follow dielectric boundaries. All of these effects are mercurial and difficult to predict; the reliability of sky or ground wave HF propagation can depend on the time of day, the weather, the number of sunspots. All of this makes HF radio a bit of a pain in the ass, but it can be worth it to achieve a feat that higher radio bands cannot: propagation beyond the line of sight.

As a rule of thumb, radio emissions in the VHF band and above behave much like light. Many materials are more transparent to RF than they are to light, but still, most modern radio communications will not propagate beyond the horizon, over a hill, or even past a sturdy building. An HF transmission, by contrast, can be received around the globe in good conditions.

HF radio thus appeals mostly to users that desire long-range communications with minimal infrastructure, and that have the sophistication (of operating practice or technology) to handle the vagaries of HF. The usual suspects are militaries, who fall more on the side of technical sophistication by using computer-driven link establishment systems, and amateurs, who enjoy the complexity of the operating practice. Other major HF radio applications include international broadcasting (often of either national or religious propaganda), intelligence and law enforcement agencies, and communication with ships and aircraft at sea. Nearly all of these applications are giving way to satellite communications, but the relative simplicity and low cost of maintaining HF equipment, and its independence from vulnerable satellites, give it enduring appeal to government users.

Let's consider a few interesting examples of these government applications, although they are not the focus of this article. Military radio is a curious combination of secretive and well-documented. The US military possesses multiple major radio systems, but is theoretically consolidating onto the Joint Tactical Radio System (JTRS). JTRS is an infamous military acquisition debacle and has run vastly overbudget and behind schedule while failing to deliver on many of its promises, but is now in daily use and consists of a diverse lineup of software-defined radios that can operate a variety of modes across many bands. In other words, it is a conceptually fairly simple system that hides enormous, combinatorial complexity in its software. This is modern military tradition.

Non-military systems are more recognizable to those without a background in 1990s military technology programs. One of the largest civilian government HF radio systems is COTHEN, the Customs Over-The-Horizon Enforcement Network. COTHEN was constructed, as the name suggests, by Customs and Border Patrol. It is now widely used by other federal law enforcement agencies with remote field operations, as well as by the military when cooperating with law enforcement agencies. The principle day-to-day business on COTHEN is drug interdiction by CBP and the Coast Guard. COTHEN employs second-generation Automatic Link Establishment (ALE), a popular system developed by the military to allow HF radios to "discover" working frequencies between two locations. Besides various mobile radios, COTHEN has fixed radio sites throughout the country, including one in the high plains east of Albuquerque.

There are many smaller HF radio systems operated by executive agencies, mostly for continuity of operations. Many are integrated into SHARES, a joint system sponsored by the Department of Homeland Security. For a more specific example, the Department of Energy has installed HF radio equipment at many of its facilities including national laboratories, infrastructure sites, and the historic AEC campus at Germantown. The DoE operates its own ALE network, but most (and very probably all) of its sites are also seconded to SHARES. DoE also makes use of HF radio for communications with Office of Secure Transportation vehicles.

We understand that there are government applications of HF radio, that's probably no surprise to anyone. But what about commercial applications? The complexity of HF operations, the size of the antennas, and ready availability of other communications options (like the internet) limit the appeal of HF to business users. Still, there must be some? Obtaining a license to use HF radio is a reasonably simple procedure, the FCC has allocated a number of HF ranges to the IG (industrial/business pool) service. As is usual in the IG service, frequency allocations are not exclusive and there may be other users. Interestingly, FCC regulations place a significant break point at 25MHz: 25MHz to 30MHz is technically HF, but FCC rules don't really differentiate between these frequencies and the more common business pool uses in VHF. Below 25MHz, though, special rules apply.

47 CFR 90.266(b):

Only in the following circumstances will authority be extended to stations to operate on the frequencies below 25 MHz:

(1) To provide communications circuits to support operations which are highly important to the national interest and where other means of telecommunication are unavailable;

(2) To provide standby and/or backup communications circuits to regular domestic communications circuits which have been disrupted by disasters and/or emergencies.

As is often the case in federal regulation, there are some additional terms that require a little closer reading. 47 CFR 90.35, which governs the Industrial/Business Pool radio service, has a table of possible frequency allocations. For the range below 25MHz, the table specifies the following restriction, in part:

(c)(i) Only entities engaged in the following activities are eligible to use this spectrum, and then only in accordance with s 90.266:

(A) Prospecting for petroleum, natural gas or petroleum products;

(B) Distribution of electric power or the distribution by pipeline of fuels or water;

(C) Exploration, its support services, and the repair of pipelines; or

(D) The repair of telecommunications circuits.

Available bandwidth at these low frequencies is already rather constrained by the allocations, but the situation is worse than it appears. HF propagation behavior mean that radio operators seldom have their choice of anywhere in the HF spectrum; usually there are only limited "windows" in which propagation is good. It would not take very many users to create congestion in this valuable long-range spectrum, so licenses are limited to users without other options.

Unsurprisingly, special restrictions below 25MHz mean that frequencies just above 25MHz are quite popular. For example, from 25MHz-25.5MHz you can find a veritable who's-who of the petroleum industry, who use HF radio for communications with off-shore oil platforms. You also find some other peculiar licenses in this range. For example, Ritron is a manufacturer of radio equipment and holds a license for the use of 25-50MHz for the purpose of demonstrating and testing that equipment. This 25-50MHz range is more or less "low band VHF," which was formerly in reasonably common business use, but is now becoming rare. Online discussion leads me to believe that it may not be possible (or is at least very difficult) to obtain IG licenses for the low band today, but some people that had them continue to renew them.

When I say "people" here, I mean it. One of the more common types of licensee for this range is... people, filling out their application with a title of "self" or "person." Although it is public record I am hesitant to give names or addresses of these people, but it explains a lot about them that you can almost always (invariably, from my spot-checking) find an amateur radio license for the same person. I have known some amateur radio operators that obtained their General Radiotelephone Operator license, a broad license for maintaining certain types of commercial radio equipment, more or less for the hell of it. I suppose obtaining a low-band IG license is similar, and adds some more bands to your potential operations.

Let's limit our consideration further, then, to the rarefied frequencies below 25MHz. Besides special justification, applicants for these frequencies are limited to certain emission types (generally narrow 2.8kHz emissions), must use equipment capable of tuning across the entire range, must submit their written communications plan, and are prohibited from testing or exercises that exceed seven hours per week. There are relatively few such licenses, the ULS returns just 61.

I totaled up the licenses by user type. For companies that provide radio services, I categorized them with the industry they normally serve, except when that industry was emergency communications itself. This sometimes required a bit of a subjective call, as we'll see when looking at some specific licenses. But here are license counts by type:

• Telecom providers: 23
• Electrical utilities: 15
• Emergency communications/disaster relief contractors: 11
• Petroleum: 7
• Railroads: 2
• Ranches: 1
• Weird: 1

Let's discuss these a bit by category. Telecom providers are a fairly obvious user group, as are electrical utilities. Both types of organizations operate infrastructure over large areas and will be expected to begin recovery quickly after a natural disaster or another event that disrupts conventional communications infrastructure. These licensees include AT&T, with the single largest license count (9), Pacific Bell dba AT&T California at the second largest (4), down to smaller entities like the Grand River Dam Authority. A notable selection is National Grid USA Service Company, which despite its generic and almost sketchy name holds a fixed location license for the Nine Mile Point Atomic Power Station among other power plants.

Verizon New York Inc. holds a license for a number of fixed locations including an inconspicuous brick building (reminiscent in its design of early telephone infrastructure but likely today a remote exchange) in Philmont, NY and a mountaintop site near Schenectady. The license seems to cover multiple telephone exchanges, only some of which have apparent HF antennas... some of the locations listed may be historic, nearly all commercial HF licenses are old, with renewal histories stretching back to the beginning of online records in 2001. Besides, virtually all of these licenses include either a nationwide mobile or nationwide temporary fixed location, making the listed locations less important than they might otherwise be.

Most licenses are also nonspecific as to frequency. It is the nature of HF radio that any given frequency will not reliably provide good propagation. The frequency lists on commercial HF licenses routinely stretch on for multiple pages of 20 ranges each, giving operators ample choice. Besides, the CFR requires these licensees to be frequency-agile across the band, in part because the FCC may require them to stop using a given frequency at any time.

The next largest category of licensees are companies that provide communications services to relatively nonspecific customers. Some, such as L3Harris, are principally in the defense industry but likely also provide services to infrastructure providers and regional governments. A few are tiny, like Hazard Zone Technology LLC, which does business from a residential address. Judging by forum discussions of the FCC's approach to HF licensing, it is possible that some of these smaller licensees are largely fictitious entities created to entice the FCC to issue a sub-25MHz license despite the restriction to emergency communications. While not conclusive, the fact that the same individual holds both a general radiotelephone license and an amateur extra license with a vanity call sign is certainly suggestive of a certain personality. There are several such examples, not an inconsiderable portion of the 61 total.

Others are familiar names in an unfamiliar context. Cisco Systems holds a license that lists their San Jose and Research Triangle Park campuses, besides a nationwide mobile location. This license is likely intended to cover the use of HF equipment as a backup point-to-point link for customers of fully managed industrial communications services, but it's hard to say exactly. They have apparently demonstrated a mobile communications trailer for emergency response coordination at conferences.

Just those three categories get us into a long tail. A railroad, CSX, holds two licenses. A ranch holds one; it's unclear how the ranch would qualify under the requirements but they may have held the license long enough to be grandfathered. The justification listed on the license is simply farm operations, not a 90.266 justification statement as found on most of these. The sub-25MHz restrictions have applied since 1983, making it difficult but certainly not impossible to hold a grandfathered license. One license is held by a missionary transportation group, they may have also held the license since before 1983 and list a location in Guam. They likely use HF to communicate with facilities on outlying islands.

There is exactly one license that I have described as "Weird." It was issued to the Bran Ferren Corporation in 2000. Bran Ferren is a bit of a character, a former executive at Walt Disney Imagineering who apparently has a side business of building off-road vehicles. This helps explain the justification statement, "MANUFACTURER AND DEVELOPER OF ALL TERRAIN COMMUNICATIONS VEHICLE." I would like to know exactly which vehicle this relates to, but the Bran Ferren Corporation keeps a low profile as compared to Ferren's main business venture, Applied Minds. Bran Ferren Corporation holds an active USDOT motor carrier number, but has had zero vehicles inspected in the last two years. That may not mean anything, they are listed as a private (not for hire) carrier and inspections may not be required. It's all a bit of a head-scratcher.

These 61 licenses for sub-25MHz commercial radio represent only a tiny fraction of the activity in the HF band. Besides amateur radio, a long list of government users are authorized to use HF radio by the NTIA, rather than FCC. Indeed, the NTIA master file includes at least hundreds of entries under 25MHz, more detail will have to wait on my finally finishing the parser for the more recent format they have used for FOIA disclosures (universal rule: if you spend many hours writing tools to parse a PDF export of a relational database back into a relational database, they will change the format of the PDF).

High-frequency traders have created renewed interest in HF radio, because of its low latency for global communications and the increasing ease of implementing automatic link negotiation with SDRs. Sniper in Mahwah has some well-known writing on this topic. To date, the FCC has authorized this activity only on an experimental basis. In 2023, a group called the Shortwave Modernization Coalition (SMC) and consisting of a group of HFT firms submitted a petition for rulemaking to allow regular use of the 2-25MHz range. The petition opened docket RM-11953, which remains open. Most recently, the FCC conducted a series of meetings between the SMC and federal spectrum users to discuss the impacts of such a new radio service.

Various documents filed by SMC do contain interesting details. SMC members are operating at least fourteen experimental HF sites, with one operating since 2016 and most since 2020. The median transmit power (EIRP) is 21.5kW, and the experimental licenses authorized 5.06-30MHz while SMC members conducted most activity between 6.675 and 21MHz. The ARRL and various amateur radio operators have filed comments opposing the change, a competing HFT radio operator has discussed a counter-proposal that would impose performance obligations on commercial HF radio operators ("use it or lose it" rules). The FCC has not yet produced a Notice of Proposed Rulemaking, the next step in the process. They are not obligated to, and it is possible the proposal will not reach that stage. For its part, the federal government itself has weighed in (in the form of comment from the NTIA), and has requested that the FCC either extensively study how such commercial HF use would mitigate interference with federal users, or exclude the use of any frequencies allocated to federal use. This includes certain bands like the Radio Astronomy service allocation at 13MHz that exist as a matter of federal policy due to foreign agreements. For my own part, I am skeptical that the FCC will act on the SMC petition unless the scope of the SMC's proposed use is reduced.

Finally, it is worth noting that these commercial HF licenses do not represent the full extent of private industry use of HF radio for continuity of operations. Some critical infrastructure operators have been sponsored by federal agencies as operators of SHARES stations. However, SHARES documents suggest that there are relatively few of these stations (around 100), suggesting that they almost completely overlap with commercial HF licenses. State and municipal governments also operate HF radio stations, which are generally licensed under public safety radio services. A curious exception is the City of Lafayette, Louisiana, which holds an IG commercial license for HF frequencies. I suspect that license is actually for the use of the publicly-owned Lafayette Utilities System (it lists electrical distribution as justification), and was issued in the name of the City of Lafayette for bureaucratic reasons.