Weird shortwave radio signal

September 7, 2007 6:38 PM

Screwing around with my shortwave radio tonight, I found this signal. [MP3] Anyone care to shed some light?

It sounds distinctly like a conversation between two or more parties, but the voices are all scrambled up. Is that essentially what it is? Or maybe aliens? Or something more mundane?

posted by knave to technology (22 comments total)

Sorry, it is mundane. You were probably on AM, and that was a Single Side Band transmission.
SSB on Wikipedia
posted by nikko at 6:51 PM on September 7, 2007

I picked up what sounded like mangled Morse code. Other than that, you should've tuned in better to pick up the voice.
posted by hammerthyme at 6:57 PM on September 7, 2007

nikko's explanation makes sense. I did tune in as best I could, it just was an elusive signal for my little tuner. It's a handheld FM/AM/shortwave radio and yes, it has no sideband support.
posted by knave at 7:08 PM on September 7, 2007

Is this recording now in the public domain?
posted by univac at 7:53 PM on September 7, 2007

As far as I'm concerned, feel free. I don't know about the original broadcasters of it, however.
posted by knave at 7:58 PM on September 7, 2007

Yep. Just an overmodulated mix of off-frequency Morse and voice single-sideband transmissions, with a healthy dose of electromagnetic interference.
posted by mykescipark at 8:59 PM on September 7, 2007

Just an overmodulated mix of off-frequency Morse and voice single-sideband transmissions, with a healthy dose of electromagnetic interference.

Sorry to not contribute, but I had to comment that this is scary as shit. Almost as creepy as numbers stations, even if it is benign.
posted by datacenter refugee at 9:06 PM on September 7, 2007

It's kind of neat that it's Morse code. Does anyone know who would be transmitting the Morse code that knave picked up?
posted by rio at 9:28 PM on September 7, 2007

I'm not that active on the HF (shortwave) bands, but yes, it sounds like you're off frequency and quite possibly in the wrong mode. Possibly in between a few frequencies.

Any idea what frequency you were on/around at the time, knave? Based on the fact that it sounds like a conversation and not a one-sided broadcast, I'd hazard a guess that it's on the ham bands, and thus the CW is from there too. (This is really a big assumption, though.) And just to throw my no-code Technician ham radio expertise in the mix, yes, that intermittent beeping (more like a squeal at this frequency) is definitely Morse code.

For what looks like a home ISP hosting the MP3, you have a pretty fast upload.
posted by fogster at 10:04 PM on September 7, 2007

Okay, well no ham geek like me can let it go without messing around with the MP3 and seeing what can be done.

At 1:30, all the noise drops out for some reason, and I'm able to copy "The Delta Lima..." In all likelihood, a ham radio operator was calling CQ and got multiple responses. He was able to copy a "DL" in the mix, so he's calling for the station with DL in their callsign to respond.
posted by fogster at 10:10 PM on September 7, 2007

At about 50 seconds, I also copied a "CQ Contest." And at 1:23 or so, "Kilo Alpha Henry." I'm not well-versed enough in Morse code (CW) to copy it, although if someone had the time it could be done more easily than me trying to pick out the voice.

It's 'just' a bunch of ham radio operators engaging in some sort of contest. (I'm not sure which--the only big one I'm aware of this weekend is VHF, not shortwave.)

I might add, you've got strong interference throughout most of it. Any idea what it was? Did something in your house kick off for a second 1.5 minutes into the recording? You'll have a much more enjoyable SWL experience if you can figure out the noise source and fix it. I've found that my furnace and one of my old computers spews noise everywhere, but it could be many other things too. (Including things beyond your control like power lines.)
posted by fogster at 10:24 PM on September 7, 2007

Inverting the audio spectrum used to be used as a primitive voice scrambling technique (it's the same effect you'll get from listening to a SSB conversation on the wrong sideband). It's simple to do with analog electronics, and it makes the speech surprisingly unintelligible, but it can still go through standard voice channels (eg telephone lines).
posted by hattifattener at 11:51 PM on September 7, 2007

univac, when you mix that up (as I assume you're going to do) please post it to MefiMusic. I know there is an amazing club track hiding in there.
posted by anastasiav at 10:09 AM on September 8, 2007

Weird to read people so excited about something that seems so ordinary to me. Also, using such sounds in music or mixes also seems like old hat to me. There was a crew doing it at our college radio station in the late 1980s and I'm sure it was done before that.
posted by Mo Nickels at 10:43 AM on September 8, 2007

@anastasiav: I think it's fine as-is. The OP should release a compilation of his finest experimental/noise music.
posted by univac at 1:19 PM on September 8, 2007

If you enjoy weird shortwave sounds, I highly recommend Myke Weiskopf's (mykescipark from above) blog Shortwavemusic. Lots of interesting music and clips.
posted by extrabox at 2:36 PM on September 8, 2007 [1 favorite has favorites]

I'm with Mo Nickels. You hear this kind of stuff all the time just tuning around looking for more interesting content. This is why I spend most of my life proselytizing shortwave.

(Thanks for the shout-out, extrabox!)
posted by mykescipark at 3:17 PM on September 8, 2007

Can I use this sound in a song? I'll give you credit where it's due.
posted by tehloki at 4:29 PM on September 8, 2007

fogster, to answer your questions... I don't have that kind of noise everywhere, it's just this particular signal was really weak for me. I can get a lot of stuff loud and clear. Actually, when I recorded it, plugging it into my laptop's mic port caused a lot of noise until I unplugged the power cable to my laptop (running on battery was much better).

I did some minor cleanup in Audition, using a noise sample from around 1:30, which is why the noise drops out there (the noise was a perfect match for the noise reduction). I also compressed the loudest parts, and then normalized the whole track. It's a marked improvement from where it started, but still, as you heard, barely comprehensible.

Thanks for all the informative answers here. tehloki, like I said earlier, do whatever you want with the mp3, I'm not claiming any ownership of it.

Yeah, my ISP rocks.
posted by knave at 7:41 PM on September 8, 2007

Oh, as far as frequency... I can't be precise about it (silly analog tuner, not very accurate), it was somewhere around 7.1MHz. Going back there now, I can here the same morse code, but no voices.
posted by knave at 8:17 PM on September 8, 2007

Around 7.1 MHz you'll routinely find CW from the US mixed with voice from some other countries. (Please correct me if I've gotten minor details wrong, speaking from memory only.)
posted by JimN2TAW at 11:48 AM on September 10, 2007

Mike,
You were probably picking up some side band or intermod signal. I only listened to part of it, but a good clue to what was being said is the cadence of the speakers. If you do a reverse intermod study from the Fq. you were at you will get an idea of who or what was transmitting.

Or, some of the distortion could be from the fact that you were monitoring 7.1MHz(40 Metres) band with a hand held radio. Your SNR or C/Kt and EbNo are going to be just baked using the set up you have. But it does sound cool.

Or, maybe the tennis courts across the street are giving you an elephant cage effect and you are picking up The Mayor on his new radio gig.
posted by MapGuy at 7:38 AM on September 22, 2007