Let’s solve another interval signal mystery!

Last month, we published a post asking SWLing Readers to help Brian (W9IND) identify an elusive interval signal. Turns out, the interval signal belonged to the Voice Mirror of the PTT Habana, Cuba station.

This month, SWLing Post contributor, David Crawford is asking for help to ID another interval signal which likely belongs to a utility station. David writes:

In follow-up to the La Habana utility mystery, here’s another one from the same era, 14985 kHz or thereabouts. Somewhere along the line I came to the conclusion that it might be El Salvador, but I don’t remember what led to that. The [recording embedded below] isn’t my own recording of it.

The tune is composed of individual DTMF tones, and when I was a bored youth I discovered that it could be played on an AT&T desk touch tone phone by pressing two keys at a time to remove the second tone. This one would repeat for hours at a time, interrupted by manually patched telephone calls.

Readers: Can you positively ID this interval signal? If so, please comment!

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4 thoughts on “Let’s solve another interval signal mystery!

  1. Dean Bianco

    Oh, sorry….here is an audio file to verify my claim:

    For whatever reason, I am unable to copy-and-paste the exact url to the audio file, so here’s what you do to listen to it:

    1. go to: utilityradio.com
    2. click ‘station data’
    3. click ‘Europe’
    4. click the ‘ear’ graphic on the line for Spain
    5. click the ‘ear’ graphic for CTNE Madrid
    6. click the ‘ear’ graphic on the third line down the Willi Passmann mid 70’s recording.
    7. play!

  2. Dean Bianco

    Hi Everyone,

    Mystery solved!

    This is the “interval signal” (more accurately, a placeholder with a musical station identifier) for the Compañía Telefónica Nacional de España (CTNW) from Madrid, Spain. They were a point-to-point HF radiotelephone terminal that provided overseas telephone and telegraph services in the days before satellites became common. As a young SWL, I would receive all manner of strange musical identifiers for these utility stations. Most of these HF telecommunication services had gone to satellite by the early 1980’s. The HF bands were chock-a-block with signals, whether they be broadcast or utility services.

    Glad to help!


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