Category Archives: Radio History

Hackaday: The Cold War-Era Survivable Low-Frequency Communication System (SLFCS)

Oscar-Zero Missile Alert Facility Minuteman ICBM Launch Control (Wikimedia Commons)

Many thanks to SWLing Post contributor Dennis Dura, who shares the following article about Cold War–era low-frequency communications, from Hackaday:

During the Cold War, the U.S. developed the Survivable Low-Frequency Communication System (SLFCS) — a radio network designed to function even after a nuclear attack. Using long-wavelength LF and VLF signals that can travel vast distances through ground and ionospheric waveguides, SLFCS provided a way to deliver emergency launch orders when all else failed. The system’s immense towers and buried loop antennas reflect an era when reliability was paramount — even under atomic conditions.

Read the full article on Hackaday by clicking here.

Video: The Origins of the SOS Distress Signal

Many thanks to SWLing Post contributor Fred Waterer for sharing this video from the YouTube channel “Today I Found Out” about the origins of the SOS distress signal:

How Did ‘SOS’ Become The Universal Distress Signal?

Three dots. Three dashes. Three dots. Even if you don’t know a single other letter of International Morse Code, chances are you immediately recognized the unmistakable rhythm of “SOS”. It is the universal distress signal, understood in nearly every country and language and appearing everywhere in pop culture including songs by artists as diverse as ABBA, Rihanna, and Great Big Sea. And with good reason: endlessly versatile, SOS can be tapped out on a telegraph key or spoken aloud over voice radio, flashed using a signal mirror or flashlight, written out in the snow or sand, or – if you happen to be held under duress – blinked out with your eyelids. But how did this seemingly random string of letters come to be the universal code for shit hitting the fan, and do the letters actually mean anything? Well, tune your radio transmitters, warm up your signalling fingers, and let’s find out, shall we?

Author: Gilles Messier
Host: Simon Whistler
Editor: Daven Hiskey
Producer: Samuel Avila

Click here to view on YouTube.

Algeria on Shortwave – Then and Now

Many thanks to SWLing Post contributor Dan Greenall, for sharing the following guest post:


Algeria on Shortwave – Then and Now

by Dan Greenall

In the early 1970s, Radiodiffusion-Television Algerienne ran a modest shortwave service (no English) mainly for North Africa, the Middle East, and Europe. A copy of their schedule from the 1972 World Radio TV Handbook is shown.

As a fledgling DXer in 1971, I was fortunate to hear their signal on 9510 kHz from my listening post in southern Ontario, Canada. Even better, they responded to my request for a QSL with this attractive card.

Fast forward a quarter century to 1996. The international service of Radio Algiers could be heard at times here in eastern North America on 15160 kHz with broadcasts that included English. Here is a brief recording from November 3 of that year that I am lucky to have saved.

In July 2022, two new 300 kW transmitters located at Ouargla and Bechar were put on the air after several years of planning. These were to be used for the Radio Coran service in Arabic, but in May 2023, Ifrikya FM (the African Voice) was born with the objective of providing a pan-African voice by broadcasting educational, informative, and cultural programming from an African perspective.

Although there is no English, they can be spotted on shortwave on 13640 and 13855 kHz after their 1900 UTC sign on. If you can hear the same programming on these two frequencies, you will know you have them.

Here are two recordings made on October 19, 2025 using a KiwiSDR near Sao Paulo, Brazil. They were made one hour apart, the first at 2000 UTC and the second at 2100 hours.

13855 was noticeably stronger than 13640 on this receiver.

A Deep Dive Into the NATO Phonetic Alphabet

Many thanks to SWLing Post contributor Fred Waterer, who writes:

I’ve subscribed to this channel for some time. This video, which dropped the other day, will be of relevance to both SWLs and HAMS:

Rob does some deep dives into language. Including the surprising origins of many words in English and the lingering influence of both Anglo Saxon and Norman French.

Cheers

Fred

This is a brilliant video. Thank you, Fred!

The 90 metre band – Then and Now

Many thanks to SWLing Post contributor Dan Greenall, who shares the following guest post:


The 90 metre band – Then and Now

by Dan Greenall

A few decades ago, the 90 metre shortwave broadcast band used to be full of interesting and challenging-to-hear DX signals. In the 1974 edition of The Complete Shortwave Listener’s Handbook, author Hank Bennett reports on what you might expect to hear on these frequencies. There is a copy of this book on the Internet Archive.  Here is a link to that specific page.

Also, this sample page from White’s Radio Log in the 1972 Communications World magazine shows a number of stations that could be logged in 90 metre band.

Here are a few links to recordings from my personal collection that have survived through the many years.  These were all made between 3200 and 3400 kHz from my listening post in southern Ontario, Canada.

[Note: Click on each broadcast link to open the associated Internet Archive page with more info.]

Radio Bougainville, PNG 1971

Radio Rabaul, PNG  1971

Radio Santiago, Dominican Republic 1971

Radio Libertad, Santiago, Dominican Republic  1971

Action Radio, Guyana Broadcasting Service  1972

Radio Christian Voice, Zambia  1996

Malawi Broadcasting Corporation (MBC)  1997

Radio Maya TGBA, Guatemala  early 1970’s

Radio Exitos, Dominican Republic  1971

Today, it seems that only a handful of stations can be found broadcasting in the 90 metre band.  These would include WWCR in Nashville, the Voice of Indonesia, KCBS Pyongyang and Radio Mosoj Chaski in Cochabamba, Bolivia.  As well, the Canadian time signal station CHU still continues to use 3330 kHz.

A recent recording of Mosoj Chaski Radio, a Christian broadcaster logged using a remote SDR in Lima, Peru, is presented here.

Although not in English, listen carefully and you can hear them give their frequency of 3310 kHz in the 90 metre band as well as their location of Cochabamba, Bolivia.

Australia Solved Remote Learning Seventy Years Ago—with Shortwave Radio!

Many thanks to SWLing Post contributor David Iurescia for sharing the following article about one of my favorite topics, which we’ve covered in the past.

Long before Zoom classrooms or remote-learning platforms existed, Australia was already teaching across the outback via radio. This article from Education Daily explores how the School of the Air began in 1951 using shortwave radio and evolved into one of the world’s most advanced distance education systems—connecting students across half a million square miles.

It’s a brilliant look at how necessity inspired real innovation in broadcasting and education.

Click here to read the full article at Education Daily.

A Radio Postcard from Seoul

Many thanks to SWLing Post contributor Mark Hirst, who shares the following guest post:


A Radio Postcard from Seoul

Hechi is a mascot for the Seoul Metropolitan Government

by Mark Hirst

I recently spent a very memorable week in Seoul, motivated to travel there by Hallyu or the Korean Wave, a cultural phenomena exemplified by the TV show Squid Game, animated movie K-Pop Demon Hunters, boy band BTS, and girl group Blackpink.

While I can credit Netflix and its huge library of Korean TV and film content for introducing me to K-drama, it was KBS World Radio and its Weekend Playlist programme on shortwave that led me to K-pop.

Early on in my holiday planning, I discovered that KBS has a public exhibition called KBS ON located in their headquarters building. Later during the trip, radio would appear unplanned in one of the other museums I hoped to explore.

Travelling to Seoul of course was a unique radio listening opportunity to hear and record stations that would otherwise require a Web SDR or internet streaming. Armed with a relatively recent copy of WRTH, I was able to compile a list of radio stations with the intention of making some short audio and video recordings.

What follows is a description of my experiences at KBS ON, some historical references to radio at the National Museum of Korean Contemporary History, and notes about the radio stations I was able to hear during my stay.

All photos are my own.

The Korean Broadcasting System

The Korean Broadcasting System or KBS is the national broadcaster of Korea, providing radio, TV, and internet based content to its national audience. KBS World is the outward facing arm of the organisation providing similar services to an international audience.

The headquarter buildings of KBS are located in Yeouido, an area of Seoul that also hosts Korea’s National Assembly Building. Technically a river island, Yeouido is bordered by the Han River, offering spectacular views of central Seoul and a skyline familiar to K-drama fans everywhere.

The main KBS building is a short walk from Yeouido station on Line 5 and Line 9 of the Seoul metro system. Your route takes you through Yeouido Park where you can see a preserved Douglas C-47 cargo plane dating from the Korean War.

The main building sits along side several other KBS related areas including the KBS Hall and KBS Art Hall. Even to the untrained eye, it’s obvious that the facility is communications related with a prominent red and white antenna tower on the main building, with red scaffolding on an adjacent block housing another tower and communication dishes.

Other notable locations at the site include a roadway and building entrance where K-pop idol groups arrive every Friday to record Music Bank, a programme that showcases the latest hits of the music genre. This photo opportunity is so popular with fans that it has a dedicated playlist on the KBS World English YouTube channel.

KBS ON Exhibition Hall

The KBS ON Mural featuring the mascot Kong

The KBS ON exhibition is part of a range of locations promoted by the official visitor guide to Seoul, details of which can be found here.

Accessing the exhibition is through distinctive blue bordered doors into a large reception area. The exhibition proper then begins at the top of a short flight of stairs.

Although all sections of the tour are in Korean, section overviews are also provided in other languages. QR codes link to audio commentaries to provide the remaining explanations for non-Korean visitors.

The audio commentary supports the following languages:

  • Korean
  • English
  • Simplified Chinese
  • Japanese
  • Bahasa Indonesia
  • Vietnamese
  • Spanish

The tour proceeds through a series of linked sections and topics which are described below.

KBS History

This section is comprised of information panels outlining the origins of KBS. Originally known as the Gyeongseong Broadcasting Station (callsign JODK) beginning in 1927, the name KBS emerges in 1945 following the liberation of Korea from Japan. KBS was established as a public broadcaster in 1973.

On Air

Through a series of large screens, this section describes the various channels KBS provides including terrestrial TV, international radio, cable, and Digital Multimedia Broadcasting, a radio transmission technology developed in South Korea.

Current Affairs / Culture programme

As a public broadcaster, this section highlights the current affairs and educational output of KBS.

Virtual Studio

This interactive section demonstrates the familiar ‘blue screen’ or chroma key technology used in news and weather forecasts. Visitors are encouraged to present their own Korean weather forecast!

Drama

The visitor is treated to a display of props and magnificent costumes from Korean period dramas, with panels and displays highlighting the role of KBS in driving growth in the K-drama industry.

Props and Costumes

Entertainment programme

Supported by large screens, this area showcases a range of local programming including talent and variety shows.

Music Bank

While the shows in the previous sections will be unfamiliar to most, Music Bank is more well known to overseas fans of K-pop. This high profile programme features live performances every Friday evening from the big names of the genre with a lottery system for fans to attend recordings.

Vertigo

This section demonstrates AI based technology developed by KBS to allow a single fixed camera to track individual members of an idol group simultaneously as they sing and dance on stage. Previously, these so-called ‘fancam’ shots required a separate camera for each performer incurring extra costs and logistics problems.

Examples of Vertigo in action are shown on large screens, featuring performances by girl groups STAYC and Illit.

Visitors can step on to a virtual stage adjacent to the displays where a single camera will automatically track your face and body without physically moving. Continue reading