At about two minutes on VOA Radiogram program 113, 30 May 2015, 1600-1630 UTC, 17870 kHz, a loud wide-band signal was heard, also centered on 17870 kHz.

I’m not sure if it was some sort of military data transmission, an HF radar system, or jamming – but why would anyone jam VOA Radiogram?

Here, courtesy of Roger in Germany, you can see the noise on a spectrum display. VOA Radiogram, with the MFSK32 traces 1500 Hz above and below the carrier, in on 17870. So is the noise, from about 1602 to 1605 UTC. The carrier of Radio Exterior de  España is on 17855. That is probably Oromo Voice Radio, to the Horn of Africa, on 17850 kHz, as well as a jammer against that station starting at 1606 UTC …

From this audio example provided by Alan in England, the noise is not bad enough to affect the decode, as seen here …

But in another audio example, provided by Mark, also in England, the noise was sufficient to cause errors in the MFSK32 decode. I was listening to the same show via a receiver in Italy, and the noise there was very strong, allowing the decode of almost none of the MFSK32 characters. 

Other modes might have performed more successfully against the noise. If the source of the noise would kindly inform me of its schedule, I can arrange for those other modes to be transmitted at that time.

And speaking of VOA Radiogram versus noise, check out this YouTube video of the same broadcast at 1600-1630 UTC, made by Tim in Colorado. At 26:15 into the recording, the VOA Radiogram transmission schedule is transmitted in Olivia 64-2000 16 dB under the closing music, and also under the local HF noise at Tim’s location. The decode mostly succeeds. It probably would have succeeded if I included more blank lines at the beginning. At the conclusion of the the music, I transmitted the thank you message, also in Olivia 64-2000, but at full level. 

At 18:08 into that same video, you can watch the SSTV PD180 mode decode. Or you can use the audio to decode it yourself.

NB: Mark in England and Merkouris in Greece note reports in DX bulletins of Ethiopian opposition stations on 17870 kHz, via Issoudun, France, being jammed by “white noise digital jamming.” See, for example, Ivo Ivanov in Bulgaria reporting to DX Listening Digest, May 27, 2015.

#shortwave