Many thanks to SWLing Post contributor, Carlos Latuff, who writes:
I have a tape with a recording I made in 1982 while listening to shortwave.
I’m not really sure if I caught some kind of polytone numbers station. Could you or your readers be able to identify it?
Post readers: If you can help Carlos identify this transmission, please comment!
First off, I don’t know how some are getting the idea that those are dual tones, they are pure tones. Secondly, without at least knowing in what band this was received, any guess what that might be would be wild at best and lastly, the receiving mode would be another vital information. The first group of tones has a different lead-in blip than the following, which might be due to a BFO retune, or on purpose as a part of the “message”, or a second station in a network.
What we know is that this was received in Brazil, and the signal doesn’t seem to suffer any ionospheric effects, just some flutter from the cassette recorder (which makes analysis of the exact tone frequences next to impossible, together with the unknown reception mode) . That would mean it was possibly local to the receiver, and that again could also mean it doesn’t have to be a transmission that was actually transmitted on HF.
Every group, or “packet” consists of a lead-in 2kHz-“blip” (except the first one, which has a longer 350hz-blip) and 3 tones of 500ms, which likely represent digits. My (extremely wild) guess would be that this is some kind of old paging/attention calling system (as e.g. used in hospitals),, which were often highly proprietary and undocumented . There are seemingly several “packets” sent in a row , which could e.g. mean it’s some industrial remote-control application, or multiple members of staff were signalled to call a dispatcher, or several alien vessels responded to a call of their mothership….
However, I remember hearing similar tones (followed by voice messages tho) coming from a nearby large university hospital that were likely transmitted on VHF, due to the close distance images could be heard on HF and it was likely AM, so they really sounded like they are on whatever frequency I had tuned in there.
Thanks for sharing your thoughts, 13dka.
Interesting your mention of industrial/hospital stuff and the lack of interference.
I remember both things nearby of my home: industries and a maternity hospital.
I surely can say I managed to listen to it in a regular AM/FM/SW radio set, on the shortwave band, but unsure about the frequency. I was a kid in that time (the 80’s) and didn’t pay attention to technical details.
The tones are defiantly DTFM as used by telephones.
It may even have been a local “wireless” telephone that was going a bit crazy 🙂 I wonder what frequency it was on .. early wireless phones were on 1.7Mhz, 27Mhz, & 40Mhz Sometimes they were FM, but also AM.
You used to be able to listen in really easily 🙂
That was my first thought as well. But only the tones similar to the one at the beginning and end and in between the groups of 3 tones appear to be dual tones of some sort. The frequencies of them don’t match up to the DTMF standards but that could be tuning issues. Even the spacing between the tones doesn’t seem quite right to be DTMF. The other tones in the groups of 3 don’t appear to be dual tones. I’ve looked at some of the older paging network and selective calling type protocols and nothing really seems to make much sense yet.
Agreed, it was a long time ago when I heard about Picolo. It does however sound like a crude attempt at data transmission using a different modulating frequency for each bit in a byte. This is to contrast with Morse code which uses different durations of carrier.
It may be Picolo is an old mult-frequency shift keying HF transmission system
Thank you for your feedback, Mangosman.
I checked the link.
Is there any audio clip for comparison?
What’s the application of this system? Military? Civilian?
https://www.sigidwiki.com/wiki/Piccolo (does not sound like a good match to me)
Agree, quite different.