Shortwave listening and everything radio including reviews, broadcasting, ham radio, field operation, DXing, maker kits, travel, emergency gear, events, and more
Many thanks to SWLing Post contributor Carlos Latuff, who writes:
Dear Thomas, I was doing my morning radio listening on the Guaíba waterfront in Porto Alegre, Brazil, when I came across this Morse code signal at 8207 kHz by pure chance. I tried to decode it using apps but didn’t get good results. As I’m not good at CW, I’m leaving the audio here so that your qualified and attentive audience can, perhaps, discover what this transmission is about. Thank you very much for your attention.
Update from Carlos:
I contacted Ary Boender, a Dutch shortwave listener and specialist in HF utility radio communications. He said:
“The recording starts with HR SVC GA NA25/XE56/ 0. You heard a Chinese military station. “HR SVC GA” is typical for the Chinese military”.
Don’s traveling DX stories can be found in his book Tales of a Vagabond DXer[SWLing Post affiliate link].If you’ve already read his book and enjoyed it, do Don a favor and leave a review on Amazon.
First, thanks to California DXer Ron Howard for his Internet sleuthing. Ron found a PDF file that specifically lists 8101 kHz as being used by the Hai Phong station in the Vishipel network, the Vietnam Maritime Communications and Electronics Company. This is a government-owned company that provides various services to the maritime industry. One of those services (and the one we’re interested in) is a network of thirty marine radio stations strung along the Vietnamese coast from north to south. The stations provide two-way marine radio communication and twice-daily scheduled weather broadcasts. All the stations use VHF and seventeen also use HF.
Vishipel’s weather broadcasts are listed on the DX Info Centre website and I had been monitoring those in my travels here in Southeast Asia. I suspected Vishipel was connected to this station but Ron found definitive proof that they use 8101 kHz and that the frequency comes from their station in Hai Phong. He also found this map showing all the coastal stations in the Vishipel network.
I’ve been wanting to record the station again, but my current location is not suitable for DXing. Since December 15th, I’ve been staying in the old city in Chiang Mai in northern Thailand. But a few days ago, I made a two-day DXpedition to a rural location outside the city and made a terabyte of spectrum recordings with my three Airspy HF+ Discovery SDR receivers.
It will take me a while to go through all that DX, but I’ve already checked for Duyen Hai. I had a very good signal from it on 8101 kHz at 1214 UTC on 08 January 2026. This broadcast was eleven minutes long, which is a few minutes shorter than the ones previously monitored. Here’s a recording of the entire broadcast.
The reception was good enough that Google Translate had no problem turning the spoken Thai into written English. The program was about new EU requirements around animal welfare. But the broadcast content wasn’t my focus. This was the first time I had good copy of the entire broadcast and I wanted to hear the ending. Here is a translation of the sign-off announcement.
Hello, ladies and gentlemen, today’s broadcast is over. Thank you for your attention, fishermen and audience. Our program is broadcast daily on the frequency 8101 kHz at 07:05, 19:05, and on the frequency 7996 kHz at 12:05. People can also contact their families and relatives via these two frequencies on all days of the week. I wish you all safe and effective sea trips. Hello, and see you again.
The wording is important for those of us who like to neatly categorize things. It proves that this is an intentional scheduled broadcast to an audience and not just a utility station unofficially relaying a broadcast. It’s the difference between whether it can be counted as a shortwave broadcast (SWBC) station or as a utility station. This ticks all the requirements to be counted as SWBC. Indeed, as a broadcast from Vietnam in Thai to a Thai audience it could even be considered as an international broadcaster!
The times in the announcement are local for Southeast Asia and correspond to 0005 and 1205 UTC on 8101 kHz and to 0505 UTC on 7996 kHz. I also found the program in my spectrum recordings coming on at 0019 UTC on 09 January. Obviously, they don’t care too much about beginning on time. Every broadcast I’ve monitored has begun ten to fifteen minutes late.
Unfortunately, I can’t check for the 0505 UTC broadcast as I didn’t make any spectrum recordings in that frequency range at that time (local noon). I’ll be sure to get some at my next opportunity. I also have questions about the 7996 kHz frequency. It isn’t listed in the Vishipel PDF, but it was listed as being used by the Nha Trang station in the 2017 Klingenfuss Utility Guide (the most recent I have).
Unless you’re in Southeast Asia, you won’t get a signal as good as the recording. But the Duyen Hai always uses the same woman announcer and the same musical interludes. Even if you just have a weak static-ridden signal, you should be able to match the music to that in the recording. So, can you catch this one at your location?
LINKS
Schedule of HF marine voice weather broadcasts at DX Info Centre. The Vietnamese listings are found under frequencies 7906 and 8294 kHz. https://www.dxinfocentre.com/marineinfo.htm
PDF file with full schedule for Vishipel stations. Times are local (Southeast Asia) times. Subtract seven hours to get the UTC time. This also includes the frequencies such as 8101 kHz that are normally used for two-way voice communication. https://vishipel.com.vn/pic/general/files/Bang%20Tan%20so%20TTDH.pdf
Don’s traveling DX stories can be found in his book Tales of a Vagabond DXer[SWLing Post affiliate link].If you’ve already read his book and enjoyed it, do Don a favor and leave a review on Amazon.
Since early November, I’ve been traveling and DXing in Southeast Asia. I’ll write more about that in a few future articles, but I came across something new that I can’t wait to share. It’s unusual and possibly might meet the criteria to be considered an SWBC (shortwave broadcast) station. If you’re in this part of the world, it shouldn’t be too hard to log. In other places, it will be a serious DX target to try for.
A few nights ago I was using the SDR-Console Data Analyzer tool to look for voice air and maritime communications in some spectrum recordings I had made on 11 December in Pakbeng, Laos. On 8101 kHz USB, I came across a strong signal with a very polished program that wasn’t anything at all like a utility broadcast. It started at 1217 UTC with a little music interlude, an announcement by a woman, a bit more music, then into some kind of documentary talk, all in an unknown language. My recording ended five minutes later, so I had no idea how long it went.
A few years ago it would have remained a total mystery but technology has given us some very helpful tools. To identify the language I began playing it into Google Translate on my phone. The second try identified the language as Thai. Here’s the English translation of the initial program announcement:
Greetings to the people and viewers. I invited the people and the audience to listen to the Duyen Hai information program broadcast from Duyen Hai Vietnam Information System. Today’s program on December 11, 2025, at 19:05 has the following content.
I heard this at 1217 UTC, which would be 1917 in Southeast Asia. So the broadcast was delayed by twelve minutes. After a brief bit of music there was a talk about the fishing industry in Hai Long Bay in Vietnam. And the language was Thai, not Vietnamese.
Here’s the audio of my reception in Pakbeng. Set Google Translate to translate from Thai to English and play it on your phone. It may take a couple of tries to get it to work.
This really sounded to me like a regular broadcast program. I started looking through the other spectrum recordings I had on hand for ones with the same time and frequency range. I found the same broadcast starting at 1214 UTC on 20 November (heard in Taal, Philippines) and at 1215 UTC on 03 December (heard in Trang An, Vietnam). The programs followed the same pattern and ended about fifteen minutes later. One program was an interview and the other another documentary. The signals were not as strong or clear so it was difficult getting Google Translate to work with them but I was able to ascertain that the language was still Thai and that the topics were fisheries and economic development.
I also have with me some spectrum recordings from an October DXpedition in Pennsylvania. I found the same program around 1215 UTC on 8101 kHz on those on 30 and 31 October. In Pennsylvania the signal was barely there but on peaks I could tell it was the same woman’s voice. So this appears to be some kind of regular program and it’s been going on for at least two months. But what is the Duyen Hai Information System and who is behind it?
There is a Duyen Hai Power Station in the far south of Vietnam. But the most likely explanation would be a connection to Vu Duyen Hai, the Deputy Director of Fisheries and Fisheries Resources for the Vietnamese government. There are numerous articles about him on the Internet. He’s been very involved in trying to make sure that Vietnam’s fisheries industry is ethically managed according to international standards.
So this appears to be some sort of regular broadcast in which the Vietnamese Fisheries department attempts to inform people in the Thai fishing industry as to what their Vietnamese counterparts are doing. To do that it would make sense to use an existing marine transmitter in the marine band since Thai fishing boats would have radios to receive this. But we don’t know if this being done officially by Duyen Hai Information Systems or if someone else is unofficially relaying the station on the marine band.
But you don’t have to be a Thai fisherman to tune in. The station is making to the eastern US. In addition to my October loggings it was logged in Maryland yesterday. So wherever you are, check out 8101 kHz USB around 1215 UTC and see if you can hear this mystery station from Vietnam.
From the early 1970’s, where sadly, some of my original logbooks went missing many years ago.
ANTEL, the Administracion Nacional de Telecommunicaciones in Montevideo, Uruguay used to use its telephone time announcement instead of a voice mirror – so they got their name ‘La Senal’ in the 1970’s. Their voice announcements in SSB mode were in Spanish and the station could be found on frequencies all over the shortwave spectrum, including 5772 kHz (CXL20), 8037 kHz (CXL21), 10770 kHz (CXL24), 11660 kHz (CXL25), 14575 kHz (CXL26), 16047.5 kHz (CXL28), and 19525 kHz (CXL33). The accompanying recording was made on January 9, 1971 on about 13550 kHz.
La Senal Uruguay Jan 9 1971 13.55:
In those days, it paid to belong to a good DX club (such as SPEEDX) or I may not have been able to identify this station at all. I was also able to get my hands on a used copy of the Klingenfuss guide to utility stations which had very detailed frequency and callsign information. Unfortunately, I let this valuable resource go a number of years ago.
And now for the mystery……
Around the same time (early 1970’s), I heard and recorded this similar styled transmission, except it was in the French language, and which remains unidentified to this day. I have no exact date/time heard or frequency information for this one.
All recordings made in Ancaster, Ontario, Canada. (40 miles SW of Toronto)
Mystery French Time Station:
Any guesses will be greatly appreciated.
73
Dan Greenall
Readers, if you can help Dan identify this recording, please comment!
I was going over a few of my old cassettes today and discovered what seems to be an interval signal, but I cannot seem to place it.
Recording:
Unfortunately, all I can tell you is that it was made sometime in 1971.
I’ve done a little checking with Interval Signals Online but no luck so far. The recording is right at the end of a cassette and you can hear the tape run out abruptly, so no ID, language or frequency info is available.
[…]Any ideas about the mystery IS?
73
Readers: If you can help Dan positively identify this interval signal, please comment!
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!
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.
Please support this website by adding us to your whitelist in your ad blocker. Ads are what helps us bring you premium content! Thank you!
