4

A local ham friend copied this strange, wide signal on 30 meters on his Flex 5000. Anybody know what it might be?

Flex spectrogram of wide, unknown signal

Marcus Müller
  • 15,910
  • 23
  • 45
Mike Waters
  • 7,948
  • 4
  • 18
  • 51
  • The 30m amateur allocation in the US says to avoid interference to fixed services outside the US. I've never found specific information on what those are, but maybe this is one of them? – Phil Frost - W8II Feb 14 '17 at 16:28
  • @Phil Frost - W8II A well known example in Europe is the DDK9 operated by the Deutsche Wetter Dienst at 10100.8 kHz. It emits RTTY weather forecasts all day, every day. – AndrejaKo Feb 14 '17 at 19:52
  • It would be handy to know where both you and your friend are located. Lots of people are here or assuming the United States, however other places than the United States have amateur radio operators. – Rowan Hawkins Feb 16 '17 at 18:39
  • @RowanHawkins SW Missouri. Look up W0BTU and W0EBV on qrz.com. – Mike Waters Feb 16 '17 at 20:58

2 Answers2

5

If I read the instrumentation correctly, this is but 20 kHz; that's pretty wide for what I'd expect for Ham operation on HF. It's not "very wide" per se. (I'd define "wide" based on the ratio of bandwidth to center frequency, and that's but 0.2% here.)

This looks a bit like an OFDM signal, especially with the hints of side lobes. 20 kHz OFDM in HF sounds a lot like Digital Radio Mondiale.

I don't know of any specific allocation of 10 MHz spectrum to broadcast licensees. However, since there is a really good free and open source DRM transmitter, built atop of GNU Radio, named gr-drm, this might very well be legitimate Ham usage; admittedly, using the high-quality channel mode for DRM does use a lot of bandwidth compared to a classical AM voice channel, but at the same SNRs, DRM sounds worlds superior if using the right voice codecs.

In Germany, for example, 10.000 – 10.150 MHz is reserved to FESTER FUNKDIENST (fixed radio service) application with "messages to one or multiple recipients" as primary, and Amateur Radio as secondary usage. p. 94 of the Frequenzplan

Marcus Müller
  • 15,910
  • 23
  • 45
  • 1
    Part §97.307(c) in the US puts some limits on occupied bandwidth for data, though I've never been able to follow all the indirection enough to really understand what the rules are. Taking 20kHz out of a band that's only 50kHz wide does seem like a dick move, especially when the entire band does not allow phone transmissions. – Phil Frost - W8II Feb 14 '17 at 16:27
  • @PhilFrost-W8II That's my thinking, too. I'll ask him when this occurred, which may help roughly determine how far away that station might have been. If it was from the USA, do the FCC rules allow modes like this on 30m? – Mike Waters Feb 14 '17 at 18:02
  • hey, looked that up in German FAT and added to the answer. – Marcus Müller Feb 14 '17 at 18:09
  • If you can record a couple seconds of raw IQ data, you might be able to run gr-inspector on it, and let it guess the OFDM parameters. – Marcus Müller Feb 14 '17 at 18:34
  • @Marcus Müller MHz of kHz? – AndrejaKo Feb 14 '17 at 19:53
  • I'm pretty sure it's not one of the HFCC broadcasters. Here's a DRM schedule directly from the source. Also, as far as I know, nobody uses 20 kHz DRM right now, due to issues with receiver availability. I'm not sure if any of the modern ham SDRs could transmit 20 kHz signal. It might be a good experiment, trying to use 20 kHz DRM and see if it manages to decode through all the other transmissions. – AndrejaKo Feb 14 '17 at 20:04
  • @AndrejaKo well, together with any TX'ing SDR that cooperates with GNU Radio, building a transmitter with gr-drm isn't hard at all. Admittedly, I don't even know what bandwidth gr-drm uses in its examples. I don't understand the "MHz or kHz" question! – Marcus Müller Feb 14 '17 at 20:30
  • @Marcus Müller Well OP is asking about the 30 m band, while you're mentioning German allocation for 10 GHz in your answer. – AndrejaKo Feb 14 '17 at 21:57
  • @AndrejaKo nope, am not. 10.000 MHz == 10 MHz; I'm using the English decimal point! (compare "0.2 %" further up in my answer) – Marcus Müller Feb 14 '17 at 22:02
  • The ham who sent me that spectrogram just told me that he copied that S9+ signal about midday. That might indicate that it was not Europe or other DX. – Mike Waters Feb 17 '17 at 01:08
  • @MikeWaters is he sure? The box in the lower left corner says "LOC 08:40" – Marcus Müller Feb 17 '17 at 01:10
  • @MarcusMüller I just shared your question with Paul W0EBV, and he agreed that it WAS at 8:40 AM Central time. Thanks for noticing that. :-) – Mike Waters Feb 17 '17 at 01:25
2

I also didn't notice that box before, but it has the date as well, 2017-01-08 in it(YMD), a Sunday.

The center is 10.130, and at S7 that's fairly strong. Also I think the actual signal is 26khz wide with the 3khz side lobes.

I don't think its DX. At 9am the sun is well up, the ionosphere E layer has merged back into D. There would be no grey line propigation in play. I realized there is a viable alternative answer...QRM.

Rowan Hawkins
  • 301
  • 1
  • 12