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