Category Archives: Articles

Guest Post: Colin’s retrospective on monitoring aeronautical communications

Map indicating location of the Shanwick OCA

Many thanks to SWLing Post contributor, Colin McKeeman, who at my request, kindly shares the following guest post:

Monitoring Aeronautical Communications – A Personal Retrospective View

By Colin McKeeman

Hopefully this article will demonstrate that this hobby involves so much more than just listening to ATC (Air Traffic Control) advising “Shamrock 105 you are cleared to land runway 28, report on finals”, etc. My life-long obsession with aviation communications has given me a considerable insight into the day to day working that this critical activity encompasses.

Despite my opening sentence, my first exposure to ATC jargon was during the early 1960’s when I discovered that local airport and over-flight movements could be monitored on a ‘tweaked’ domestic VHF receiver. I recall someone discovered that a well-known Dublin based audio retailer, could retune such sets to cover the aeronautical air band (108 to 137 MHz). As a consequence like- minded enthusiasts soon appeared at the airport carrying bulky portable sets where their regular station names on the dial had been hidden behind pieces of sticky paper with new designators ‘Dublin Centre’, ‘Shannon 131.15’, etc. Although more compact and dedicated air band receivers have been developed over the years and the basic mode of VHF transmission has remained almost unchanged, but this cannot be said of aeronautical short-wave (HF) communications.

Whilst the monitoring of local aircraft movements was a considerable enhancement to the ‘spotters’ hobby, the desire to get more advance notification of ‘interesting’ flights was always regarded as the ‘holy grail’. I can quite vividly recall the breakthrough when at 16:25 on Thursday, the 3rd October 1963, I first heard Shannon Aeradio (located in Ballygirreen, Co. Clare) working a Trans World Airways flight 741 on short-wave. This was whilst flicking across the SW1 band of my 1958 Philips, model B3X85U valve receiver (see image below).

1958 Philips, model B3X85U valve receiver

This set had two short-wave bands comprising, SW1 covering 2.54 to 7.45 MHz and SW2 spanning 6.9 MHz to 22 MHz. My reception was boosted by a length of bell wire jammed into the sets external aerial socket and pinned to the picture rail over my bed. Thankfully this was during the time when Shannon Aeradio still broadcast on AM as this set was not equipped with a BFO for single sideband reception. Suddenly it became possible to hear flights mid-Atlantic that might just route my direction, or better still land at Dublin or even Shannon (well worth the six hour round trip by car!). The next problem was that the aforementioned flight TWA741 didn’t provide identification on the tail number/registration of the aircraft involved, a key element for the ‘spotter’. (Sorry, now more maturely redefined as an ‘aviation enthusiast’!).

I then discovered that many airlines assigned their two tone SelCal (selective calling) codes to individual aircraft and since the ground based radio operator working the flights usually repeated the code when copying a position report, yet another identification opportunity presented itself. A database of code assignment was soon established, thanks to co-operative airlines and diligent monitoring of airport movements. Today these codes still provide a potential method of aircraft identification and even in cases where the SelCal may not be announced by either the flight or repeated by the ground operator, I now utilise a mode of the excellent ‘MULTIPSK’ software to decode and display the four letter characters on screen, for subsequent possible airframe tie-up. It should be noted that not all aircraft operators link the SelCal codes to specific airframes, as some allocate them to the flight number instead.

It soon became apparent that Ballygirreen was not the only aeronautical ground station that could be heard on HF and so monitoring of the oceanic activity in the various areas managed by, Prestwick, London (station sited at Birdlip, Gloucester – more on this later), Paris, Iceland, Copenhagen, Bodo, Gander, New York, Churchill, Sondre Stromfjord, Santa Maria, Madrid, San Juan, was soon being logged from their various ‘nets’. Today many of these stations either no longer transmit on HF or have been amalgamated into a single unit, e.g. Shanwick, which consolidated Shannon Aeradio and Prestwick (the London station having been previously replaced by Shannon in January 1966). By good fortune some of the major players on the North Atlantic shared common ‘Families’ of frequencies, namely Shannon, Gander, Iceland and New York in the mid-1960’s all transmitted on 5611, 5626, 5641 and 5671 mc/s and thus avoided the need for constant frequency hopping. It should be noted that Shanwick Radio is providing communication support from its location in Ballygirreen whilst the actual clearances and routing decisions are decided at the Oceanic Centre in Prestwick, Scotland, which are then relayed to the flights from the Co. Clare station.

These HF stations handle both civil and military flight movements however some agencies provide a dedicated service for their military traffic. This is particularly appropriate to the United States Air Force, who operate a vast net of HF frequencies and dedicated stations. Stepping back 20 or 30 years, activity on these channels was particularly frantic, a key facility of theirs being Croughton Radio, based in the U.K. at Barford St. John, operating on a primary frequency of 111.75 MHz, still heard today. Because they transmitted on single sideband, monitoring such activity on my old Philips set was frustrated by the lack of a BFO, although I did attempt to create a harmonic on the frequency with another set tuned appropriately. This workaround never proved to be very satisfactory but was sometimes worth the effort.

Gradually single sideband became the norm for aeronautical HF communications and so investment in a dedicated receiver became essential and I saved up for a Trio 9R-59DS and was lucky enough to supplement this with an old American BC-348 set during 1972, both of which are still in my attic. This necessitated the need to erect a more efficient external aerial and so I quickly set up a suitably matched half-wave dipole for the 5 MHz band down the length of the garden, much to the intrigue of the neighbours.

With the advent of home computing another dimension to this hobby presented itself, whilst still retaining use of the communications receiver. In the early days of commercial aviation their communications relied on W/T but by the time my monitoring commenced this had been replaced by R/T. However radio teletype (RTTY) had also become a key feature of communication between the aeronautical ground stations. Whilst Morse code could be copied directly with paper and pencil, a computer (on an in-line teleprinter) was required to copy RTTY transmissions. So in the mid-1970’s, with the help of some simple software, I managed to start decoding Ballygirreen’s remaining RTTY link with Santa Maria, their circuits to Prestwick and other centres having been withdrawn some years earlier. Shannon Aeradio transmitted RTTY to Santa Maria on 3250, 5813.5, 8145 and 11440 mc/s and received traffic from them on 5474, 10540 and 11468.5 mc/s. These circuits, like many others, fell under the umbrella of the worldwide AFTN (Aeronautical Fixed Telecommunications Network) and messages had to conform to standards and structure as laid down by the ICAO (International Civil Aviation Organisation).

An example of such a message, copied by the author from Shannon Aeradio on 22nd March 1995 sent to Santa Maria, in the Azores regarding a KLM flight number 781, where their request for a higher altitude was denied, is reproduced below. The italic text within the { } is my clarification of its structure and so does not form part of the original message:-

ZCZC SMA152 221258 {start of message no. 152 on the Shannon/Maria/A circuit at 12:58}
FF LPPOZOZX LPAZYSYX {flight safety mess’ for the Santa Maria Oceanic & ATC centre’s}
221258 EIAAZZZX {message filed at Ballygirreen at 12:58 on the 22nd}
TOD1252 {the key element of the message}
DFHM TA {selcal code DF-HM was transmitted on frequency TA, i.e. 5598 mc/s}
KLM781 RB TA MTNG F290 {the flight read back the message on 5598 mc/s & will maintain 29,000’}
EIAA RB TAQSYVA) {Ballygirreen read back on 5598 (TA) and advised flight change to 8906 (VA)}
NNNN {end of message signal}

Although the transmission of AFTN messages over HF have now ceased there is still much aeronautical activity to monitor, both on R/T or in the digital mode. Indeed the latest statistics from the Irish Aviation Authority shown that North Atlantic communications with Ballygirreen have grown by almost 9% when compared to this time last year, which represents contact with almost 945,000 flights for the first 10 months of 2016. Admittedly the format of the R/T air-ground messages have had their content shortened, especially as a result of the introduction of Controller Pilot Data Link Communication (CPDLC) procedures. Under this digital data transfer system, the ground station having established an initial R/T contact with the flight, all subsequent reporting is completed by data link and so further voice communication is dispensed with. Not all flights are CPDLC equipped and consequently R/T reports can still be monitored for the entire oceanic sector for a reducing number of operators.

Even though this precise mode of long range data communication may not be capable of interrogation by the average enthusiast, it is still possible to capture some of the aeronautical data bursts. For shortwave, this protocol is titled HFDL (HF Data Link), and for closer range the VHF equivalent is entitled ACARS (Aircraft Communications Addressing and Reporting System). To copy HFDL I use the ‘PC-HFDL’ software (Shannon operate on 11384 mc/s, plus others) and for the VHF data transmissions I use the ‘KG-ACARS’ software (the primary European frequency being 131.725 MHz). Incidentally, the United States Air Force utilise a similar HF based system called ALE (Automatic Link Establishment) but this tends to contain a lower level of information and transmissions are less frequent.

I hope this very brief overview gives you some idea of what attracts the current aviation enthusiast with an interest in communications and notably all without recourse to the Internet (except for initial access to the decoding software).

Many thanks, Colin!

If you would like further information, check out Colin’s HF blog or contact him directly at

As an aviation historian, Colin recently published a book on the history of the U.K. Birdlip communication complex, radio call-sign ‘London’ (mentioned in a post a few days ago).  The cost of Colin’s book including shipping to U.K. addresses, is €22. If you live outside the UK, contact Colin at the above e-mail address for a shipping quote.

“Hello Finland, this is Vancouver calling”

Many thanks to SWLing Post contributor, William Lee, who shares the following story from the CBC:

Hello, Finland, this is Vancouver calling: radio fans listen to CBC from 6,700 km away

When people in other parts of the world tune in to CBC Radio in Vancouver, they usually do it through our app, or online or through Sirius XM.

But some people in Finland recently picked up Vancouver’s CBC broadcast — the broadcast heard locally at 690 AM and 88.1 FM — using an elaborate antenna system roughly 300 kilometres north of the Arctic Circle in Lapland, Finland.

“It’s a few [radio hobbyists] from around Finland who have a very nice place up in the north where there’s not much neighbours which means not much interference,” Patrik Willfor, one of the listeners, told On The Coast host Stephen Quinn. “It’s like a silent band there, so even the weakest signals come through.”

The practice is called DXing, and Willfor says he’s been at it for about 25 years since a friend told him that’s what their fathers used to do when they were young.[…]

Click here to read the full article on CBC British Columbia’s website.

Post readers: Is it just me? Or do you, too, get a kick out of it when the press gets a glimpse into the seemingly-anachronistic, but still-relevant-and-rocking world of radio–?

Note that you can also listen to the audio interview with Patrik via the embedded CBC player below:


Guest Post: Richard builds a WiFi radio with the Raspberry Pi

Many thanks to SWLing Post contributor, Richard Schreiber (KE7KRF), who shares the following guest post:

Yet Another Internet Radio!

by Richard Schreiber (KE7KRF)

After deciding that an internet radio could be an important source of entertainment in our household, we formulated a few general guidelines:

  • We opted not to use an aggregator but would pick and choose stations we enjoyed and discover the URL’s ourselves. Also would be satisfied with a couple of dozen stations. Based on a recent decision to pare down the number of TV channels we were paying for, having access to hundreds of stations seemed impractical and unnecessary.
  • The price had to be affordable, thus eliminating many stand-alone, commercially available internet radios.
  • We already owned a quality portable speaker (Bose SoundLink Mini) so the internet radio didn’t need to duplicate that component.
  • Didn’t want to tie up nor be tethered to a laptop, tablet, or netbook. We predicted that would eventually lead to less and less use of the radio.

After some research, coupled with the fact I already had some experience with Raspberry Pi computers, that small device appeared to be our best choice. I had recently purchased the newer 2 B model, which has plenty of computing power, and had installed Ubuntu Linaro as the OS. (As an aside, this OS has not to my knowledge been upgraded for the latest Raspberry Pi 3). There are several other operating systems that will work just as well including the official Raspbian OS available through the Raspberry Pi Foundation.

I installed the MPD music player daemon and its client MPC, which is used to add to and delete station URL’s from the playlist, control volume, etc. An important find was the iPhone app called MPod which provides remote wireless access to the features of MPC. At the moment it is a free app for the iPhone (in my case the iPod Touch).

For portability, my Raspberry Pi is being used “headless”, meaning it is not connected to a monitor, keyboard or mouse. If maintenance is required you can use PuTTY, a SSH and telnet client, wirelessly from a Windows (or MAC?) PC, using a command-line interface. Mainly this is needed to shut down the Raspberry Pi properly before turning off the power, but it boots completely on its own when powered up. The MPod app will then load the playlist of stations and let you start playing the radio without direct access to the Raspberry Pi.

The sound output of my Raspberry Pi is connected to the auxiliary port of our Bose SoundLink Mini Bluetooth speaker. But instead of trying to implement Bluetooth on the Raspberry Pi, I took the easy way out and use a direct connection. The sound reproduction from this setup is very good, though audiophiles might be somewhat more critical.

The above represents a minimal investment if you already have a good speaker on hand. It does require some on-line research and learning at least enough to install the OS and software. The good news is that there are many websites and forums providing step-by-step instructions and helpful hobbyists willing to explain some of the more cryptic aspects. A few of the websites that I found to be helpful:

A couple of these also explain how to add a display to your Raspberry Pi internet radio.

Our Raspberry Pi radio is on each evening and has been trouble free. It is worth mentioning that this is a very portable setup, and can even be powered by a battery pack (the kind used for recharging tablets and cell phones) for a few hours. Of course you need to be near a wifi hotspot.

Thank you, Richard! What a great way to use the inexpensive Raspberry Pi. I have a spare Pi2 and an amplified speaker here at the house. Though I don’t need another WiFi radio, it would be fun putting this little system together. 

Oxford Shortwave Log: Sony ICF-SW77 vs ICF-SW55 vs Tecsun PL-310ET

Hi there, I recently posted an article regarding a couple of recent DX catches with the Sony ICF-SW77 receiver and went on to explain the background to a multi-receiver test I had started conducting, comparing it with its stablemate of the time the ICF-SW55 and, just for the hell of it, a more modern, yet modest portable in the shape of the brilliant little Tecsun PL-310ET.                                                Sony ICF-SW77

The initial results confirmed the performance of the Sony receivers to be very similar and thus the justification for the original price delta of £100 in the UK to remain in question. The first target signals chosen and in the original post were ABC Northern Territories on 4835 kHz and Radio Mali on 9635 kHz.

Sony ICF-SW55                                                        Tecsun PL-310ET

The initial results reinforced my view that the PL-310ET is a great portable for relatively small money; it managed to copy both signals, something you might not expect from what is essentially a budget receiver.

Below are links to the next 6 reception videos on the Oxford Shortwave Log YouTube channel and once again, featuring all three radios. I have used two different antennas during the testing – a 75 metre longwire and the Wellbrook ALA1530 active loop, running on batteries. The accompanying text description to the videos indicates which antenna was used.

Although the PL-310ET clearly struggled with the more ‘hard-core’ DX signals amongst those detailed below, the fact is, for less than £40 in the UK (and I’m certain even less elsewhere), Tecsun have delivered us a portable radio that really is capable of real DX. With DSP, a number of audio bandwidth filter options and great sensitivity, it’s a winner for beginners to DXing and to ‘old hands’ who want a radio in their pocket when they take the dog for a walk for example (something I do all the time – you never know when you’re going to come across the next barbed wire fence!). As for the Sonys, well I’m still not convinced one way or the other that the £100 price delta on the original price of the ICF-SW77 was worth the money – the ICF-SW55 is pretty close to it in terms of delivering discernible audio across all of the below reception videos. I’d be interested in your views and note there will be a final posting on this 3-way receiver comparison to wrap things up. In the meantime, thanks for reading/watching/listening and I wish you good DX!

Enbedded videos follow below.

Clint Gouveia is the author of this post and a regular contributor to the SWLing Post. Clint actively publishes videos of his shortwave radio excursions on his YouTube channel: Oxford Shortwave Log. Clint is based in Oxfordshire, England.

Washington Post: “A big change to U.S. broadcasting is coming”

View of the Capitol Building from the roof of the Voice of America on 330 Independence Ave., S.W.

Many thanks to SWLing Post contributor, Richard Langley, who shares this editorial from the The Washington Post:”

“FOR YEARS, members of Congress have fumed about what they regard as ineffective U.S. public diplomacy, including the failure of broadcasting operations such as the Voice of America and Radio Free Europe/Radio Liberty to match the reach and apparent influence of networks such as Russia’s RT and Qatar’s al Jazeera. A frequent and arguably fair focus of criticism has been the Broadcasting Board of Governors, the body created to supervise government-funded media outlets while serving as a firewall between them and the political administration of the day.

A radical change to that system is now coming — and it looks like one that Vladi­mir Putin and Qatar’s emir might well admire. An amendment quietly inserted into the annual National Defense Authorization Act by Republican House leaders would abolish the broadcasting board and place VOA, RFE/RL and other international news and information operations under the direct control of a chief executive appointed by the president. The new executive would hire and fire senior media personnel and manage their budgets.

[…]The point of board governance was to prevent direct political interference in programming by the White House, State Department or other agencies. It was a guarantee that for decades has helped to attract journalistic talent to the broadcasting organizations, as well as listeners seeking reliable information. The board of governors had serious problems: Its members served part time, and not all took their duties seriously. But the system’s biggest flaw was remedied three years ago with the creation of a chief executive position.

The new reform, driven by House Foreign Affairs Committee Chairman Edward R. Royce (R-Calif.), enhances that executive’s power and makes him answerable to the White House rather than the bipartisan board. A new advisory panel will be created, but it will be toothless: Its members will also be nominated by the president from a pool provided by Congress.[…]”

Click here to read the full editorial at The Washington Post online.

Also, Richard points out this article in BBG Watch which highlights comments from Dan Robinson.