Automatic Link Establishment (2G ALE)

The Kiwi SDR now includes the ability to decode ALE 2G, so it’s probably a good time to look at where ALE is used, and how this can add to your SWL.

In the UK we have deployed a MOD system for communicating with assets called Defence High Frequency Communication System (DHFCS), which operates on many HF frequencies depending on conditions. The system is operated and maintained by Babcock, and uses high power HF transmitters to communicate beyond the line of sight.

Within the UK, the system is divided into three stations of paired transmitter and receiver sites. ‘UK North’ comprises sites at Kinloss Barracks (RX) and Crimond (TX) in northeast Scotland, ‘UK Middle’ at Forest Moor and Inskip  (TX) in northern England and ‘UK South’ at St. Eval (TX) and Penhale Sands (RX) in southwest England. Three overseas stations, with two sites each, are located in CyprusAscension Island and the Falkland Islands.

One such transmitter site is RAF Inskip this location is also used to transmit the Volmet HF signal on 5450 kHz

Image provided courtesy of Google Street View

I started by using the Kiwi to monitor activity on frequencies defined as UK RAF in the picklist, you can see how the decode is presented below. You select a decoder from the far right-hand side (beside the select band pull-down) and select ALE 2G. You then need to set up some options in the bottom left, a selection is shown for UK DHFCS which is most likely to provide some results.

The data can be logged to a txt file, and saved for review later. Here is a typical file

[2021-11-17 08:53:58 5295.00] [Sounding THIS WAS] [From: XSS] [His BER: 1]
[2021-11-17 08:56:34 5466.00] [Sounding THIS WAS] [From: XSS] [His BER: 3]
[2021-11-17 09:00:55 4510.00] [Sounding THIS WAS] [From: XSS] [His BER: 2]
[2021-11-17 09:06:12 6992.00] [Sounding THIS WAS] [From: XSS] [His BER: 10]
[2021-11-17 09:09:26 3640.00] [Sounding THIS WAS] [From: XSS] [His BER: 0]
[2021-11-17 09:10:31 6251.00] [Sounding THIS WAS] [From: XSS] [His BER: 15]
[2021-11-17 09:13:23 4239.50] [Sounding THIS WAS] [From: XSS] [His BER: 0]
[2021-11-17 09:26:52 5466.00] [Sounding THIS WAS] [From: XSS] [His BER: 4]
[2021-11-17 09:29:34 4047.50] [Call] [From: XCF] [To: XSS] [His BER: 2]

Over the course of a few hours I found the following active frequencies were noted in (KHz)


If you would like to read more about my Kiwi SDR or use the Kiwi for direction finding of mystery HF signals you can find more information in the links provided.

More information on the UK DHFCS system is in this document.

You can buy your own Kiwi SDR online

If you found the information useful and you wanted to say thanks, then you can buy me a coffee 🙂

73 Dave

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