Endangered Shortwave Stations

Last week, when talking to my friend and fellow shortwave archivist Thomas Witherspoon about using software-defined radios to capture and preserve parts of the shortwave spectrum, he and I suddenly stumbled upon an idea: creating a curated list of endangered shortwave radio stations. We could use such a list, we thought, to focus our own efforts and those of the community on archiving the transmissions that were the most likely to disappear in the near future.

Shortwave Radio Audio Archive endangered stations page - http://shortwavearchive.com/endangered/

Thomas went ahead and quickly put together a draft version of this list, available here, and I added a few items to it. However, it's difficult to get up-to-date information on the stations' closure plans, as the organisations that sponsor shortwave broadcasters usually don't give much notice when deciding on funding cuts, so we will have to figure out a way of keeping it current (perhaps we can also use this list as a point of contact for whistleblowers?).

The list has already helped me to prioritise my shortwave recording activities. For the past four days I have been using my indoor SDR set-up (FunCube Dongle Pro+, MacBook Pro running Windows on VMWare and SDR#, plus the entire anti-interference set-up, described in one of my earlier posts) to record a small window of the shortwave spectrum that contains two critically endangered stations: the Voice of Greece (9420 kHz) and All India Radio (9445 kHz). These are late evening transmissions that I can't capture from the park for practical reasons. Some effort was required to tune the equipment for stable indoor reception:

Noise elimination at work. pic.twitter.com/TWJs8PQs2G

— London Shortwave (@LondonShortwave) 22 April 2016

The effort has already paid off, however: having recorded close to 14 hours of the Voice of Greece, I noticed that the station went off the air again last night. VOG is known for its irregular broadcasting hours, so not much surprise there, yet it's hard to predict when it resumes its programming. Hopefully, fellow enthusiasts will get in on the act and record the broadcasters that are teetering on the brink of shutdown. What stations do you think are critically endangered? Please leave your thoughts in the comments section!

Denoising old shortwave recordings with SDR#

Readers of this blog may already know that I live in a densely built-up part of London, which is a very harsh environment for listening to shortwave radio indoors. I have come up with some RFI mitigation strategies, but these work best when the underlying radio signals are still relatively strong. That is because once a signal dips below the ambient noise floor there isn't much one can do to recover it.

At home, I enjoy listening to "blowtorch" signals like All India Radio, Voice Of Greece and Voice of Turkey (although occasionally I try my luck and listen to weaker stations). Still, sometimes the propagation is poor and even these stronger transmissions start fading into the noise. This can be especially disappointing when I start recording a particular transmission and then go off to do other things, only to find out later that the recording is heavily ridden with static. Many of my night-time recordings have ended up this way and until recently I thought that they were generally beyond "repair".

Enter SDR#. It turns out that it can process a regular audio WAV file just as if it were a real-time radio signal, meaning that its noise reduction plugins can be used to clean up the sound.

SDR# settings for denoising audio. Click the image to enlarge.

To do this, open the WAV recording either as an IQ file or using the FilePlayer front-end plugin. Chose the RAW demodulation mode and click play. You can then experiment with IF Noise Reduction parameters to find a setting that offers a good tradeoff between the noise filter strength and the amount of audio artefacts.

To give an example, here's a rather noisy recording of All India Radio I grabbed last New Year's Eve:

And here it is after noise reduction with SDR#:

Although there are a few DSP audio artefacts in the denoised version, I do like the end result and I'm sure I will be repairing quite a few more of my noisy recording this way.

Radio from the Korean peninsula

With tensions flaring up on the Korean peninsula once again, here are some Korean broadcasts I have extracted from my recent spectrum recordings:

KBS World Radio (English): April 6, 2016

KBS World Radio recorded in London, UK on April 6, 2016 at 1559 UTC, on the frequency of 9515 kHz using AirSpy, SpyVerter, SDR# software and a 2 x 6m long wire dipole antenna. The transmitter has a power rating of 250 kW and is located in Kimjae, South Korea. In the news: a possible new nuclear test planned by DPRK, as suspected by South Korean intelligence services, GPS jamming by North Korea.

Click here to download the recording // Link to the original SRAA submission

Voice of Korea: April 9, 2016

Voice of Korea, DPRK recorded in London, UK on April 9, 2016 at 1638 UTC, on the frequency of 11645 kHz using AirSpy, SpyVerter, SDR# software and a 2 x 6m long wire dipole antenna. SDR#'s IF noise reduction plugin was used to mitigate the severe levels of static arising from poor propagation conditions. The transmitter has a power rating of 200 kW and is located in Kujang, DPRK. In the news: North Korea's testing of a new intercontinental ballistic missile component, the ability to mount nuclear warheads on such missiles.

Click here to download the recording // Link to the original SRAA submission

KCBS Pyongyang: April 9, 2016

Korean Central Broadcasting Station, Pyongyang recorded in London, UK on April 9, 2016 at 1601 UTC, on the frequency of 11680 kHz using AirSpy, SpyVerter, SDR# software and a 2 x 6m long wire dipole antenna. SDR#'s IF noise reduction plugin was used to mitigate the severe levels of static arising from poor propagation conditions. The non-directional transmitter has a power rating of 50 kW and is located in Kanggye, DPRK. This is a domestic service targeted at North Korea's local population. Soothing North Korean music is being broadcast, presumably to put the listeners at ease after the incendiary war-time rhetoric.

Click here to download the recording // Link to the original SRAA submission

Very Weak Signals: Hearing Xi Wang Zhi Sheng

AirSpy SDR and the SpyVerter upconverter

As you may have read in one of my previous posts, I enjoy using my portable SDR setup to record entire portions of the shortwave spectrum for later analysis and extraction of individual broadcasts. I am currently evaluating the AirSpy / SpyVerter SDR combination for this purpose (I shall be covering my experience with this radio in more detail in one of my next posts). One of the nice things about this SDR is that it lets me record an entire shortwave band reliably onto my tablet without maxing out the latter's processor. This evening I used it to capture one hour's worth of the 31 meter band in my local park, and once I got back home I immediately started poring over the recording in SDR# on my laptop. Late afternoons and early evenings are an exciting time to be tuning around the bands in Western Europe as many broadcasts from the Far East, South East Asia and the Pacific come in quite clearly:

— London Shortwave (@LondonShortwave) 6 April 2016

I managed to pick up New Zealand quite well despite their signal being unusually weak (I confirmed this whilst out in the field by comparing my reception of it with TwenteSDR's, using my smartphone). However, the real surprise came when I ventured just below the start of the band and stumbled upon a very faint signal at 9155 kHz. Being able to rewind and fast forward through the spectrum recording is a fantastic feature of SDR#: using it I quickly found the part of the transmission where the station ID was announced. I had tuned into none other than Xi Wang Zhi Sheng ("The Sound Of Hope" in Cantonese), a clandestine station with a 100-watt non-directional transmitter located in Taiwan, according to short-wave.info, regularly jammed by China.

Assuming the short-wave.info listing is accurate, 100W is a tiny power rating by shortwave listening standards and is more suitable for ham radio operators (most international broadcasters start at 50 kW). To reach far, hams typically employ directional antennas that can concentrate the radio signal into a narrow beam. By contrast, The Sound of Hope is reported to have a non-directional transmitter, which ought to make reception even more challenging. And challenging it was, until I turned on SDR#'s noise reduction feature that made the sound pop out from the static:

I am quite pleased with this catch. I have uploaded the full recording to the Shortwave Archive and you can listen to it in the embedded player below:

The Sound of Hope: April 6, 2016

The Sound of Hope (Xi Wang Zhi Sheng) recorded in London, UK on April 6, 2016 at 1600 UTC, on the frequency of 9155 kHz using AirSpy, SpyVerter, SDR# software and a 2 x 6m long wire dipole antenna. The transmitter has a power rating of 100W and is located in Taiwan. This transmission is usually a difficult catch in Europe due to its low power rating and non-directional nature. SDR#'s IF noise reduction plugin was used to make speech more intelligible.

Click here to download the recording // Link to the original SRAA submission