Tag Archives: Interval Signals

Reading an interval signal in the waterfall

I’ve been doing a lot of SWLing with the new Icom IC-705. I suppose I’ve not much to post here other than to simply say: I think Radio Exterior de España‘s interval signal looks brilliant on the ‘705 waterfall. I captured this at the end of their scheduled broadcast around 22:02 UTC today.

Of course, the audio was pretty nice, too. Their interval signal is unmistakable:

I’ll admit: I’m loving the native recording capabilities of the IC-705. This came straight off of the MicroSD card. Bandwidth was set to 9 kHz.

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CPRM Lisboa: Another mystery signal solved

In response to our latest mystery utility signal challenge, SWLing Post contributor, Dean Bianco replies:

This is the musical marker for CPRM Lisboa, a radiotelephone terminal that provided overseas telephone and telegraph communications in the days prior to satellites.

I remembered the non-broadcast HF frequencies being loaded to bursting with many of these radio services. When not scrambled for privacy, one could hear a telephone call in progress. Instead of a musical IS such as this one, most were loop tape voice ID’s in several languages (almost always including English). So naturally these musical loops made it quite difficult to know what exactly one was hearing, to say the least!

To verify check out the following embedded audio file made by Willi Passmann  (via the excellent UtilityRadio.com website):

Once again, thanks to Dean Bianco for solving yet another mystery! Obviously, Dean is a Black Belt SWL and DXer!

FYI: I’ve received a number of emails from readers who really enjoy these mystery signals. Since we all seem to have more time at home these days, I’ll plan to keep them coming!


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Yet another mystery utility signal to solve–!

Back by popular demand!

On our quest to solve UNID utility signals, SWLing Post contributor David Crawford, is asking for help again to ID yet another interval signal. David writes:

Here’s yet another memorable utili-tune from the deep archives here, again not my recording, origin uncertain.

This one has a date, time and frequency on the filename [19670811-2347-15910-VM unID] and therefore would have been 1967. I heard this one myself occasionally also, which would have been sometime during the mid-to-late 1970s. It would have overlapped with the same time period during which CTNE was using the 14985 kHz tune previously provided, so despite the broad similarity I would assume it wasn’t them. Unless of course they used different tunes for different circuits:

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

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Dean solves second interval signal mystery

(Image source: Madrid.org)

In response to our second mystery interval signal challenge, SWLing Post contributor, Dean Bianco replies:

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!

To verify his claim, Dean shares the following embedded audio file made by Willi Passmann in the mid 1970s (via the excellent UtilityRadio.com website):

Well done, Dean! Thank you once again for coming to the rescue!

In case you didn’t know, dear readers, Dean Bianco is a force to be reckoned with in the shortwave radio world. 🙂 This year, he won the 3rd Annual Fest Trivia Quiz at the 2020 Winter SWL Fest! An impressive accomplishment, indeed. Not only that, but Dean’s an incredibly nice guy, great friend, and always willing to help out those new to the hobby!

Thank you, Dean!

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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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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, UtilityRadio.com.

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!

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Help Brian identify this 1970s era interval signal

[Mystery solved! Click here to read the update.]

Many thanks to SWLing Post contributor, Brian (W9IND), who writes:

I want to thank you for stirring a memory that I never thought I’d relive – even though it still doesn’t solve the mystery of what the heck I was listening to in the first place!

Back in the early 1970s, I was a teenage SWLer with a curiosity for the worldwide signals that emanated from the speaker of my shortwave radio. Bitten by the SWLing bug after stumbling across Radio Nederland’s Bonaire relay station, I spent many a happy hour twirling the dial in search of fresh game to hear and QSL.

But on one such occasion (I’m going to guess it was in 1971), I was surprised and fascinated by what sounded like a snake-charming horn playing notes at random. Stranger still, the transmission would seemingly go off the air for a couple of seconds and then return to play the strange melody again. I chalked it up to one of the countless beeps, hums and other electronic noises that often appeared on utility frequencies in those days.

I never recorded it, I never had a clue what it was, and I never heard it again.

Until recently. On the Shortwave Radio Audio Archive.

A couple of weeks ago, while looking for old shortwave interval signals from the 1970s, I saw a recording marked “Unidentified interval signal 1” listed right after the interval signals of Deutsche Welle and Radio Nederland.

“OK,” I thought. “Sounds like a challenge. Maybe I can even help figure out what it was.”

Then it played … and I almost fell off my chair! I literally sat with my mouth open as the long-lost sounds of the “snake-charming horn” played again. Could it indeed have been an interval signal – and if so, for what station?

I wanted to contact the person who recorded it, but then I learned the sad news that Mr. Greg Shoom is no longer with us.

So I remain mystified, probably forever. But it sure was fun hearing that weird recording again! Thanks for the memories.

Let’s see if an SWLing Post reader can help, Brian!

I know of at least a dozen readers who are experts on all that is interval signals, so hopefully someone can listen and ID this one.

I’ve embedded audio from this SRAA recording below. Note that the unidentified interval signal can be heard between time marks 1:27 – 2:07 in the following recording:

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


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