Mystery Solved: Readers identify curious interval signal

Yesterday, we published a post asking SWLing Readers to help Brian (W9IND) identify an elusive interval signal (click here to read that post).

We received dozens of replies–thank you so much!

Many readers immediately identified the tune as some sort of utility station placeholder for Point To Point communications. Turns out, they were correct.

Many thanks to Dean Bianco who was the first reader to solve the mystery.

Dean discovered that the interval signal was for the Voice Mirror of the PTT Habana, Cuba.

Dean verified it via Rainer Brannolte ‘s excellent website,

Here’s the audio clip from Rainer’s website:

Here’s a link to the PTT Habana Cuba page which also includes two other audio clips of the PTT service.

Rainer even includes a scan of his verification letter:

Click to enlarge (Source: Rainer Brannolte)

This morning, I received a number of responses from readers confirming PTT Habana–thank you so much!

Not only have we helped Brian ID the station, but now there’s also one less UNID audio sample on the Shortwave Radio Audio Archive.

In addition, I’m sure my friend Greg Shoom–who originally posted the recording–would be very pleased with this community effort.

Now I need to find some more shortwave archive mysteries to solve!

Spread the radio love

6 thoughts on “Mystery Solved: Readers identify curious interval signal

  1. Gareth Woods GW4JPC

    I remember, back in the 1970s, there was such a station that used, what sounded like, endless piano exercises to keep its’ frequency clear. I have never been able to identify it and have not heard it in any archive. There were two distinct pieces of music, very repetitive, one used much higher notes than the other. Does anyone have any idea what the station was and whether there are any recordings of it?

    1. Henryk Florczy?ski

      Hi Gareth, I am a DXer since 1974 – maybe I can remember/recognize this interval signal. Can you send me the link to this record?
      Best regards

  2. Bob LaRose W6ACU

    Interesting! I also remember that there was a “Voice Mirror” (repeated voice recording) from that station that would run for hours between calls. They had an SSB point-to-point link, apparently with Europe, in the morning and early afternoon and the reording even gave the full identification as “CMO-56 Radio Corporation of Cuba”. The frequency was in the 18.4 MHz region and once I heard them calling Berlin to set-up a call. They were very strong in New York in those days!

  3. Brian, W9IND

    I also note with interest that Rainer’s PTT Habana Cuba page states that all such recordings were made in 1971.

    That lines up exactly with my estimation on when I first heard the station. However, the strange music played much more slowly than the one on Rainer’s website (featured here). The archive recording by Greg Shoom more accurately represents the one I first heard nearly 50 years ago.

  4. Brian, W9IND

    Many thanks, Thomas, and a hat tip to Dean for his shortwave sleuthing!

    I feel somewhat vindicated in surmising, even as a teenager, that this was a utility station and not an interval signal for a shortwave broadcaster. However, it also wouldn’t have surprised me to learn that the “snake-charming horn” sound belonged to some obscure regional station with a name like Radio Outer Hyderabad. Just listen to the similarity between the Cuban station and an actual snake charmer:

    And Thomas, as for which shortwave archive mystery to solve next … now that you’ve helped identify “Unidentified interval signal 1,” might I suggest “Unidentified interval signal 2” on that same recording?

    73, guys!

  5. Dan Srebnick

    Fabulous Thomas and thank you Dean!

    This takes me back to my childhood when I used to hear this sound coming out of my father’s shortwave receiver. As an 8 year old boy, I always wondered what this mystery sound was and tried to figure it out as an adult, but could only rely upon memory as I had no recording and could not find one that matched my memory. But this is very close to what I remember. I wonder if there were other melodies.

    This makes my day!


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