Tag Archives: Mystery Signals

Patrizio seeks information about mystery signals he’s discovering across the HF bands

Many thanks to SWLing Post contributor, Patrizio Cardelli, who has discovered some interesting signals on the HF bands and is seeking information about them.

A little background: Patrizio asked me about these signals a few weeks ago and based on a quick glance at the spectrum and waterfall images I assumed it was DRM (Digital Radio Mondiale). I was wrong, of course. Had I looked at the actual frequency and bandwidth, I would have immediately realized is was not DRM. My email load has been so heavy as of late, and my time to reply at such a premium, I rushed through the reply–my apologies, Patrizio!

Patrizio followed up with this message:

Hello Thomas,

I hope this message finds you well. I wanted to share my recent radio exploration based on your advice. I followed your suggestion and investigated a sample signal within the 60-meter band, specifically settling on the one at 4.962 kHz.

I attempted to decode it using the Dream software but encountered no success. It seems this isn’t a Digital Radio Mondiale (DRM) transmission. To rule out local QRM (interference), I tested various Kiwi SDR receivers across Europe, both to the south and north of my QTH. Interestingly, I managed to pick up this signal everywhere, with a stronger intensity noted in the northern locations.

I’m eager to publish this article to find out if other Shortwave Listeners (SWL) have been able to decode this transmission. Additionally, I’d like to mention that similar signals, either continuous or intermittent, are present on various HF frequencies.

I look forward to any insights or experiences others in the community might have regarding this intriguing signal.

Audio sample:

While I recognize these signals now, and I’m sure most of you who cruise the bands have seen/heard these as well, Patrizio is a relatively new SWL, turns out, and I thought it might be fun exploring just what these signals are. 

Readers: If you know what these signals are, please comment. Indeed, I’m sure there are a number of SWLing Post readers who have hands-on time with generating these signals as well in a past life or current career. Let’s explore!

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Midway Island Radio Terminal 1971: Digging up the past and a mystery signal…

Many thanks to SWLing Post and Shortwave Radio Audio Archive contributor, Dan Greenall, who shares the following post:

Midway Island Radio Terminal 1971 – digging up the past

It was a brief “military style” transmission on approximately 14.85 MHz shortwave, logged sometime during 1971. And I still had a recording of it!


I wondered if there was any chance of confirming what exactly I had heard way back then, so I recently decided to try a little bit of detective work. My first contact was with Nick England, K4NYW, who runs a “hobby” website about U.S. Navy communications in the 1950’s and 1960’s. He was good enough to put me in contact with a Midway navy vet, Charles E. “Chuck” Kinzer, who writes:

“…it could be a “long count” test for one of the transmitters at the Naval Communication Unit transmitter site where I worked.

When I was there (1966-1968) they installed two log periodic fixed antennas, one pointing generally east (Washington DC) and the other generally west (toward Vietnam).

Each was connected to an AN/FRT-39 10 KW transmitter. And for the most part, always connected to the same two transmitters. (We had an antenna patch panel and could mix and match most any transmitter to most any antenna.) It is my understanding that they were used by the Security Group on Eastern Island (one of the two Midway Islands which are Sand and Eastern). They were set up for single sideband voice. (Most of the other AN/FRT-39s were set up for multiplexed TTY tones on both sidebands with suppressed carrier. 16 channels on each sideband.)

From time to time, they would tell us they wanted to do a “long count” and we would set the power level of one of the transmitters. As they did the count, we would set the power level of the peaks of the voice close to the maximum transmitter power. You could see the various meters flail up and down to near maximum along with the voice. This would be mainly the “PA Plate Current”, “PA Plate RF”, and PA Output” meters on the 10 KW final.

We couldn’t hear the voice, just see the meter activity. It would help if the person knew the frequency. If it was NOT an amateur radio frequency, it might have been one of those long count tests on one of those Navy transmitters. ….”over 50 years ago” sounds reasonable for that exercise. I assume the usage of that particular transmitter/antenna setup lasted to the end of the Vietnam war, at least.

Incidentally, when this was first set up, we had instructions to put X transmitter on Y antenna and so forth when they started testing the two new antennas. They would ask to do a “long count” test where we would set the power levels. Then shortly after they would start shouting into the microphone raising the power level too high and the transmitter would trip off. We asked them exactly what they were trying to do and, for secrecy I guess, they would not tell us. After a while, they figured out they were using the two antennas backwards. For example, they were trying to transmit east off the back side of the west facing antenna. These were VERY good antennas and very little power was wasted in the envelope going backwards.

I don’t know if this helps. Rather amazing that there is a recording existing like this. You never know what is going to pop out of the woodwork.”

Chuck later added that he might ask someone else for a little help. In the 1970’s, I used to own a guide to utility stations by Joerg Klingenfuss, that had lots of great frequency information, but sadly, I decided to part with it a number of years ago.

Please listen to the audio file of the transmission above from 1971, maybe some readers might weigh in with their thoughts on this? Please feel free to comment.

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Can you help Carlos identify this station?

Many thanks to SWLing Post contributor, Carlos Latuff, who writes:

Hey Thomas, just got a broadcast (Nov 5, 2023) on 21640 kHz, from 15h30 to 16h00 UTC here in Rio de Janeiro. A potpourri of pop rock songs and then a female voice says ‘this is the end, have a nice day’.

Both Carlos and I assume this could be a shortwave pirate. If you can help Carlos identify this station, please comment!

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Can you help Bob identify this mystery signal?

Many thanks to SWLing Post contributor, Bob (K7ZB), who shares the following note and recording: 

Hi Thomas,

I recently started using an SDRplay RSP1A with their new software release SDRconnect.

Quite a nice piece of work and my first foray into SDR after 60 years of analog radio (K7ZB).

Today I was listening to WWV on 10MHz and it was being interfered with a strange type of digital signal that pretty much covered the band.

I finally tracked it down to 9.979MHz, recorded it and sent it to a friend who did a bit of audio analysis on it by expanding out the signal to look at individual bursts.

I certainly don’t recognize the modulation although it sounded like a form of CW in burst mode.

I am just curious if you have any insight on this signal or where I might go to find out more about it.


Gilbert, AZ

Post readers: Can you identify this signal? If so, please comment and thank you in advance!

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Off-Air Recording: Can you help Pete ID this broadcast?

Many thanks to SWLing Post contributor, Pete Jernakoff, who writes:

Last Saturday evening, I was cruising through the SW bands and came across music and talk on 2640 kHz, a rather odd (I would think) frequency on which to find such a broadcast format.

The music was of the soft pop variety (for example “Vou de Taxi” by Angelica; “A Time For Us – Love Theme from Romeo and Juliet” by Jack Jones; “A Lua E Eu” by Cassiano), and it sounded to my ears that the on-air talent (male) was speaking (between songs) either in Portuguese or in a Brazilian dialect of said language.

I have attached an audio clip of this broadcast [see below] which begins at 0158 UTC (on 26-March-2023). The recording is a little over 13-minutes long and ends when the signal abruptly leaves the air.

Note that there is a seeming mention in the recording of the words ‘Brazil’ and ‘Brasilia’ at the 4:40 and 5:03 time points, respectively. I have no clue where this signal originated, and I’m hoping that you or one of your many readers might be able to help ID this one. As far as I’m aware, there is no station that broadcasts on this frequency at least with this kind of programming. The signal seemed too strong to be a harmonic of a station broadcasting on, say, 1320 kHz. Perhaps a pirate? A mystery to me…

Thanks for sharing this recording, Pete! 

If you can help Pete ID this mystery recording, please comment!

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Can you help Paul identify this station?

Many thanks to SWLing Post contributor, Paul Walker, who writes:

I had a strong s9+20 signal on 9595kHz Mon Jan 9th, 2023 here in Alaska in the 1900UTC hour with nothing but a repeating loop of the same island-y like music.  The track was about 3-5 minutes long and there was no station announcements of any kind between the one repeating track. It was gone by 2000UTC. No one is listed on eibi, short-wave.info, shortwaveschedule.com or HFCC Raw data for this frequency at this time.

Who is it? It sounded too clear and good to be China, but I suppose that’s possible.

Readers: if you can help Paul, please comment!

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Can you help Rob identify two mystery signals on the 20 meter band?

I received the following message from my buddy Rob (NC0B) who is trying to identify a couple of signals on the 20 meter band. Rob kindly gave me permission to post his email here on the SWLing Post with the idea that someone may be able to help him solve this:

The following is a description of two odd digital signals observed on 20 meters with transmission modes I do not understand. They may not amateur transmissions, but I have no way to decode them. They stick out like a sore thumb on 20m in the Extra portion of the phone band. The time of day on August 20th was between 11:50 AM and 12:00 PM MDT.

Two weeks ago I was in QSO on 14,170 kHz and occasionally there was the same 10 kHz wide digital signal but centered on 14,171 kHz. It sounded like the old Russian jammers buzz saw modulation. Those signals from decades ago were much wider, and or course we didn’t have high resolution spectrum scopes back then. Today the same transmissions occurred several times, and more than once a minute for about 5 seconds each. In total the transmissions may have occurred on and off for about 10 minutes.

Then after a few 10 kHz transmissions a different signal came on the air a few times with what looked like a digital modulated carrier plus digital sidebands on each side of the middle signal.

Look at the attached JPG file and I’ll try to make sense out of it:

The waterfall image lasts about 50 seconds on the Icom IC-7610 set on slow. There are two different signals to differentiate in this image. The signal I observed two weeks ago and today is 10 kHz wide and today spans from 14,178 to 14,188. It shows up in green on the band scope, and just under it in blue on the water fall for about 3 seconds of the approximate 5 second transmission. You can also see at the bottom of the waterfall the previous transmission that has about 4 seconds worth saved on the waterfall running off the bottom. The horizontal span of the scope was set to 5 kHz per division.

Once the 10 kHz wide signal started, I went to Dual Watch so I could listen for KL7QOW on 14,170 kHz for a sked, and hear the buzzing signal on 14,183 kHz in SSB mode. That frequency placed the carrier position of the SSB 2.8 kHz bandwidth in the center of the 10 kHz wide signal.

Soon after I started observing the relatively flat spectrum of the 10 kHz signal, a new digital signal appeared about 3 kHz lower in frequency. At first it had a much stronger center modulated carrier about 2 kHz wide and then two symmetrical digital signals on each side within about a 6 kHz total bandwidth. I wasn’t able to capture the best picture of the 2nd signal as it appeared to be tuning up. The amplitude difference between the central signal and the separate sidebands initially was about 15 dB. Vertical divisions are 10 dB.

On the waterfall you can see the second type of signal is centered on about 14,180 kHz. The modulation depth of the outer pairs of signals were not constant, possibly due to selective facing. QSB was quite significant at this time at least to Alaska. You can see there was a short break of a few seconds in the 6 kHz wide signal. Every time I have seen the 10 kHz wide signal its amplitude across the transmission bandwidth has been fairly constant, always of short duration, and repeating several times within 10 minutes before terminating.

Does anyone have any idea what either of these transmissions are? I have heard of email digipeaters, but I would not think their bandwidth would be this wide.

Rob, NC0B

SWLing Post community: Please comment if you can help Rob ID these signals!

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