curmudgeon“Whatever happened to HF radio?”  (No, not HD radio, HF radio!).  “High Frequency” radio flourished back in the days before “radio” became “wireless,” when perhaps it was better known as “shortwave radio!”    And if you are old enough, the term “shortwave” can still conjure up some half-forgotten memories.  Of crackling news broadcasts from far away countries and announcers with odd accents.  Or of a ham in his “radio shack” on a cold, snowy winter evening, bent over a chassis lit dimly by glowing vacuum tubes, sending Morse dots and dashes winging over a freezing, moonless north Atlantic ocean toward Europe.  Or perhaps the staccato warbling of radio teletype, moving the news between continents.

Shortwave radio served the troops on many battlefields!
Shortwave radio served the troops on many battlefields!

Well, even with all the new telecom technology that has come along, HF radio (3 – 30 MHz, roughly) is still alive and in daily use, but in ways perhaps not entirely foreseen back in the pre- and early post-World War II era.  And in ways perhaps not known to the younger generation, who has never lived in a world without instant IP-based communications.

Why did HF radio survive?  Because of several of its inherent natural attributes.  HF signals can cover long distances, often thousands of miles, without intermediate relay points.   With its simplicity and direct, point-to-point (or -multipoint capability), it needs no space satellites, no tower-top repeater stations, no fixed land line networks that can be destroyed by terrorism or natural disaster.  The Curmudgeon remembers, back in the 1960s, listening on 15 MHz with a simple receiver and outdoor wire antenna to the NASA manned space flight tracking network as it followed an early Apollo or Gemini mission.  (This was prior to NASA’s establishment of its own data/comm relay satellites.)  As the ground tracking stations on the HF net closed down and signed off after spacecraft splashdown, the direct voice transmissions from every tracking station around the world were clearly received!

That’s what makes it so valuable for backup radio networks and emergency/disaster service: HF radio is just a transmitter on one end of the circuit, a receiver on the other, with only an electromagnetic field flowing between them!  Today’s HF radio equipment is solid-state, reliable, inexpensive, compact, transportable, and quickly adaptable to changing needs.  HF’s attributes have not been forgotten by the military, who keep operational and contingency HF networks alive and ready.  Or by disaster relief agencies, who know too well what happens to more sophisticated facilities-based communications nets after the hurricane, earthquake, or fire.

It’s not uncommon in summer to hear hams on the air on 14.325 MHz (the “20 meter” shortwave ham band) relaying current weather/storm reports as part of a disaster net operated by the National Hurricane Center in Miami.  Reporting from the path of an oncoming major storm, they can be heard to transmit,   “My commercial power is out, the land-line and cellular telephones are gone, the Internet is dead, and I’m running on auxiliary generator power.  But I’ll stay on the air and relay my local weather data as long as the fuel holds out and the storm doesn’t take my antenna.”  Yes, this still does happen.

While HF radio is still very much at work, it’s changed considerably from what you might remember.  The (non-broadcast services) voice mode first shifted from analog AM to analog single side band transmissions (which are vastly more power efficient!) and is now going into digital transmission (Digital Radio Mondial is coming into the international broadcasting service and other, non-broadcast service digital voice modes are in testing).  The introduction of ALE (Automatic Link Establishment) technology now permits unattended monitoring of a network channel, automatic set-up of the optimum HF frequency for the intended path and time of day, and selective calling of individual stations on the net.  Among other places, it is used for comms between ground tracking stations and transoceanic transport aircraft.

Shortwave beams worldwide.
Shortwave beams worldwide.

On the character transmission side Morse Code, which used to be sent and received by human operators, is almost completely gone, since it’s no longer a government-mandated communications mode.  Even traditional radio teletype (5 bits/character, quasi-digital Baudot machine code) has been partially supplanted by numerous new computer-generated 8 bit/character modes, more efficient and reliable than the old Baudot.  And new computer applications allow for successful receipt of HF burst data transmissions with signal strengths that are well below the ambient noise level.

HF radio can be surprisingly useful, especially in emergency/disaster communications.  During his working career the Curmudgeon was presented with an interesting challenge: to provide disaster communications to company field crews working in very remote parts of the service territory, well outside the service range of the company’s established UHF repeater network and of cellular telephone service.  (The obvious choice, satellite telephone, has disadvantages: operating cost, and lack of “push to talk” multipoint capability).  The Curmudgeon’s proposed plan was to establish a single sideband voice mobile network between key field supervisors’ trucks and headquarters.  This network would operate at the low end of the HF spectrum (between 2 and 4 MHz), where it is characteristic that the local surface wave RF signal reliably “spreads out” in a circular area of a hundred mile or so radius and “flows around” obstructions into remote valleys where VHF/UHF transmissions are blocked (similar to AM broadcast radio transmissions).  Equipment, training, maintenance and operating costs to underpin the proposed network would be minuscule, operational reliability would be more than acceptable, and a simple solution involving the use of HF radio could be quickly implemented.

[Did company management adopt it?  Of course not!  They were unable to “think beyond the five dots” (at that time recently “downsized” from nine dots).  Instead they authorized and spent up to 100 times the cost of the proposed HF radio system on, first, trailer-mounted, generator-powered “emergency” UHF repeaters, to be towed to the scene of disasters.  They then followed this minor error with a major UHF repeater expansion project costing tens of millions of dollars.   “Those who cannot remember the past are condemned to repeat it.” —   George Santayana]
National Hurricane Center HF communications station WX4NHC
National Hurricane Center HF communications station WX4NHC

So HF radio continues its daily work into a new century, but not without some difficulties.  Faced with an inherently high background RF noise level (provided by both natural and man-made noise sources), the noise problems have increased in recent years.  The advent of data transmission over existing unshielded metallic conductors (i.e., Broadband over Power Lines, ADSL and VDSL, and home power wiring-based computer networking), have markedly increased noise levels in local areas, and the integrated power flux from their operations may affect world-wide background noise levels.  And poorly-constructed consumer digital devices howl on specific HF frequencies and their numbers are growing exponentially.

Still, HF radio continues in its historical assignments, modified for present needs:  back-up circuits for emergency/disaster comms, international shortwave broadcasting largely to areas of the world not yet well served by fixed IP circuits, primary voice and data comms to very geographically isolated locations, and Amateur Radio communications worldwide.  It’s all still there now, and it just as reliably will be there should satellites fail, fiber optic cables be downed, and microwave channels be loaded to saturation.

The HF radio band, one of the first portions of the spectrum used by the newly-invented radio art, is just as useful today as it was in 1900, and the Zenith Transoceanic receiver which once ruled it still lives on!

What do you think?

“Let’s keep the universe safe for RF!”

The Old RF Curmudgeon

About The Author

LBA Group, Inc. has 50 years of experience in providing RF asset solutions and risk management for industrial and telecommunications infrastructure assets. The group is comprised of LBA Technology, a leading manufacturer and integrator of radio frequency systems, lightning protection and EMC equipment for broadcast, industrial and government users worldwide; the professional consultancy Lawrence Behr Associates and LBA University, providing on-site and online professional training. The companies are based in Greenville, N.C., USA.

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