Category Archives: Digital Modes

Looking at HF OTH RADAR

Many thanks to SWLing Post contributor, Trevor, who shares this link to a blog post from Daniel Estevez describing the characteristics of HF OTH RADAR:

Most amateur operators are familiar with over-the-horizon radars in the HF bands. They sometimes pop up in the Amateur bands, rendering several tens of kilohertzs unusable. Inspired by Balint Seeber’s talk in GRCon16, I’ve decided to learn more about radars. Here I look at a typical OTH radar, presumably of Russian origin. It was recorded at my station around 20:00UTC on 8 December at a frequency around 6860kHz. This radar sometimes appears inside the 40m Amateur band as well.

Above this post you can see a waterfall plot of the radar signal. It’s the wide red signal. It is 15kHz wide and pretty strong, but severely affected by frequency-selective fading. Looking at the IQ recording in Audacity, it is clear that the radar uses pulses with a 50Hz repetition rate. This explains the characteristic sound of this radar when received with a conventional SSB radio. It sounds similar to AC hum (here in Europe, of course).

Continue reading on Daniel’s blog…

DigiFAQ Updated: An HF Digital Decoding primer and reference tool

Many thanks to SWLing Post contributor, Mike Agner, who writes:

[S]ome 20 years ago, Mike Chace-Ortiz, Stan Skalsky, myself and a bunch of other folks put together a FAQ about digital modes on radio – specifically modes going from LW way up into the UHF spectrum- called the DigiFAQ 5.3. I was responsible for the HF Software section, and as you might know, back then it was all about the hardware. InfoTech was still around, and amateur digital modes using the PK232 were plentiful. There is a PDF-based copy on the UDXF website [click here to download].

Now jump ahead 20 years or so, and things have changed considerably. Hardware is no longer king, and soundcard-driven software has taken over the market. Even receivers have changed – the desktops of old (quite apart from the current batch of ham transceivers that have general coverage radios built in) have been pretty much supplanted by Software Defined Radios. Along with that, the digital modes themselves have changed drastically with some disappearing altogether, with new ones like ALE going to the head of the pack. Too, the original DigiFAQ combined many ham-related modes along with everything else.

[O]ur original work didn’t really address some of the basic questions newcomers to this side of the hobby might have, [s]o with Mike Chace-Ortiz’s help, I have been involved in rewriting and updating the FAQ. Its approach is different – we start from topics like discussing radios, SDRs, some of the terminology you will see on mailing lists like the UDXF and much more. Only after we cover all of this do we discuss decoders – and even here, this topic is broken down even further, to include those decoders that play nice with some SDRs, and some of the tools you can use to help analyze an unknown signal.

Then we go into the modes (most are HF related, but we do touch on one or two common LW modes). We identify those modes that are dead, and separate them from the rarely used/active ones. Where possible we also supply waterfalls for each.

We also have an extensive appendix with a whole bunch of links for additional reading.

Perhaps of greatest use to newcomers is a listing of known scheduled broadcasts, so they can test what they download without wandering all over the place, hoping to find a readable signal – and potentially getting turned off when the don’t find one. We have also recovered a few articles from the old WUN archives as well as from SPEEDX (Society to Preserve the Engrossing Enjoyment of DXing – folded a long time ago) on certain digital related topics, such as discussing how to read an AMVER transmission.

It should be noted that we also sent the amateur radio digital modes to their own page for a very simple reason – while these modes are well understood (and many have their own devoted page that cover their mode far better than we can), the single biggest reason was that these modes can NEVER be encrypted (at least in the US, and likely other countries as well). Sad to say, but there are many modes outside of the amateur bands that we will never be able to read, and some whose purpose is unclear. As of this writing, many UDXF members are noting signals thought to be Russian in origin, utilizing a variation of MFSK-16, a mode generally associated with amateur radio.

Is this document complete? Not even close. It’s designed to be something of an introduction, with enough detail to hopefully draw in both the newcomer and experienced. There are new modes being identified, new networks, and even new players being found all the time. There’s still more work to be done on this, and this is yet another change to the original DigiFAQ- it’s hosted on the RadioReference wiki, where any member (with a free ID) can edit and add to it.

The URL is:

Regards, Mike

Thank you for sharing this update, Mike!

I receive a lot of questions regarding digital modes even though it’s an area of the hobby where I’m quite weak. I’m pleased that you, Mike, Stan and your team are all working to keep a reference source up-to-date for folks exploring this dynamic part of the radio hobby.

Click here to visit DigiFAQ at

Nicholas uses Android phone and $18 receiver to decode VOA Radiogram


Many thanks to Nicholas Pospishil, who shares this photo and notes:

“VOA Radiogram on 5745 kHz. No fancy equipment needed.”

No kidding! Mobile phones and tablets now have more than enough horsepower to decode most VOA Radiograms.

Nicholas uses the free AndFlmsg app for Android to decode. Note that AndFlmsg is not available in the Google Play store, you must manually install it using these directions.

The Kaito WRX911 is an $18 US receiver and AndFlmsg is free. That’s a pretty inexpensive and accessible combo!

Nicholas originally posted this image on Gary J. Cohen’s Shortwave Listeners Global.

Thanks for sharing, Nicholas!

KNL Networks is developing shortwave-powered global Internet access


Many thanks to SWLing Post contributor, Steve T, for sharing the following news from Business Insider:

KNL Networks, based in Oulu, Finland, has been in stealth mode during the past four years while developing a revolutionizing system that enables internet connection anywhere in the world – even in the middle of the Pacific Ocean – without using expensive satellite systems.
Today, KNL announced the completion of its series A funding round. The funding amounted to more than $10 million making it one of the biggest Nordic series A rounds. Creandum is the biggest investor.

[…]Facebook and Google have been exploring the possibility of bringing internet to remote locations by relaying data through a network of balloons. KNL’s technology, on the other hand, proposes the opposite: incredibly long range signals, by sending internet protocol over the radio.

KNL’s technology is already being used to provide robust internet connections to ships on the Atlantic and Pacific Oceans, but can be used anywhere on the globe for many different applications.

[…]KNL’s technology relies on shortwave radio transmissions, which can transmit data for thousands of kilometers, for a fraction of the cost of a satellite system. Accomplishing this has required the innovation of long-distance high frequency radio systems. In comparison with satellite internet, the radio technology offers the additional advantages of being easier to use, always on.

Read the full article at Business Insider.

This is very exciting news, Steve!

I’ve always had confidence that inherent HF bandwidth and data integrity issues could be addressed with time as our receivers, codecs and digital signal processing improve with each iteration.

As I wrote in, Does Shortwave Radio Have a Future?, I’ve always believed that the shortwave medium could be leveraged for international digital/data communications, and should be. In my article, I focused on Radio Canada International (RCI), which was then dismantling their shortwave transmitter site:

[B]roadcasters should not dismantle their transmission sites as Canada is currently doing. Not only is the current service originating from these sites a more reliable form of emergency communications than the Internet, should a national disaster befall us; not only do they continue to provide a broad-spectrum mode of diplomacy; but should future digital communication modes find a way to take advantage of the HF spectrum as is now under discussion, this would be most unfortunate.

Imagine a wi-fi signal with a footprint as large as several countries, digital devices with tiny fractal antennas that receive this signal containing rich media (e.g., audio and video)––these are not science fiction, but highly plausible uses of these transmission sites, even within the next decade…

We’ll be watching developments at KNL Networks and reporting updates here on the Post. Follow the tag: Shortwave Internet

Can you help Rick ID this mystery digital signal?


Photo from Rick’s location in Vernon, BC.

Many thanks to SWLing Post reader, Rick Slobodian, who writes to request help with the following:

Tecsun-PL-606I was on the beach at our lake, [where I was listening to my] Tecsun PL-606 receiver.

[On Friday, August 19, 2016 at 1800 UTC, I noted a] “beeper”: beeps at Hz repetition rate , does not appear to be data, it beeps for about a minute then there is a short data burst then beeping again for a minute or two.

This went on for over an hour.

Location of Vernon, British Columbia, Canada.

Location of Vernon, British Columbia, Canada (click to enlarge).

[The beeping covered] all frequencies between 13400-13800 kHz. [Then on August 20, it started at] start 1745 UTC and was no longer on 3400-13800 but now on
all frequencies between 12120 -12250.

What is it? [Take a listen:]

Click here to download a recording of the beeping.

My ham radio friend says there are a network of stations that send out pings that everyone in the group transmits and everyone receives. The signal strength and phase of the rx signal is correlated at each receiver station, to direction find some unknown station.

Was there such a thing during the cold war, and is it still around? What is this system and where can I find out more about it?

Thanks for your inquiry, Rick. This is outside the scope of what I understand on the HF bands, so I hope SWLing Post readers can chime in and offer suggestions.

Please comment if you can help Rick ID this transmission!