Shortwave is still the weirdest and most interesting part of radio

Those signals can travel far enough to feel like they could have come from anywhere

Anyone who has ever used a walkie-talkie or handheld radio understands how VHF and UHF radio work. Airband, marine, CB repeaters, and all the devices smartphones have now replaced are all local. As long as the receiver is not too far away or blocked by geography, you can pick up a transmission just fine. Shortwave, or HF radio, is a completely different story.

Most of what we call shortwave sits in the high-frequency (HF) range, roughly between 3 and 30 MHz. Signals within that range can travel far beyond line-of-sight. Under the right conditions, they hit the ionosphere, refract, and return as sky waves, as opposed to VHF/UHF ground waves that simply continue into space once they fly past the curvature of the earth. These sky waves can land hundreds or thousands of miles away. That is why a receiver in California can pick up a transmission that originated in Europe, Africa, or even Australia.

This phenomenon also makes browser-based software-defined radios (SDRs) perfect for hunting weird signals. Instead of buying amateur radio gear, fighting local conditions, or needing a huge antenna, you can jump between receivers around the world. If one SDR fails to pick up anything interesting in Germany, you can switch to another in South Africa and try again.

The Buzzer is the obvious place to start

UVB-76 is the longest-running radio mystery and the most reliable signal to begin with

The Russian Buzzer, better known as UVB-76, can be a bitter disappointment when first heard. Many expect to hear Tchaikovsky's Swan Lake, but instead, they get a repetitive buzzing sound that is dull and irritating. Tune into 4625 kHz using Upper Sideband (USB) mode with a KiwiSDR online, and you too can hear it for yourself.

Many SDRs close to the suspected transmission site of the buzzer have blocked out its frequency. This is likely to prevent abuse, as the frequency is commonly targeted by radio graffiti with pirate signals or intentional patterns in the waterfall. What it transmits is not as important as the reason why it exists in the first place, because we do not actually know. That is the truly unsettling part about this particular signal: someone, somewhere, is actively keeping this thing alive.

The station has been tracked since the 1970s, keeps changing callsigns, and sometimes, if you are lucky, the buzzing changes to random clips of a Russian voice. It is generally understood to be a Russian military station rather than a mystery signal, but that has not stopped the internet from turning it into doomsday folklore. The legend that it would broadcast a message just before a nuclear attack contributes to its creepy reputation.

Skyking, do not answer belongs to real military shortwave traffic

The phrase is real and can be heard at a few frequencies if you are lucky

The phrase Skyking, Skyking, do not answer is legendary online. It is real, and you can hear it if you listen to the US High Frequency Global Communications System (HFGCS) for long enough. The phrase itself means that responding stations should not reply on air, and it was popularized on the internet around 2010 when one of the first publicly accessible WebSDRs came online at the University of Twente.

Radio hobbyists explain that the message is a high-priority, encrypted broadcast heard on the HFGCS alongside routine Emergency Action Messages (EAM). Tune in to HFGCS frequencies at 4724, 8992, and 11175 kHz, and you may hear test counts, mainsail ground station broadcasts, and aircraft call signs. If you are patient, you might catch the Skyking transmission itself.

These are the signals you can try first

Some are downright creepy, some are useful, and some are just boring

For anyone starting this experiment, the best approach is to open the rx-tx.info SDR map, pick receivers that are currently under nightfall (better for signal propagation), and filter for HF receivers. Then jump around between several receivers in different locations and start the hunt for weird signals.

Why use an SDR for this? Because they are located all across the world and feature a constantly scrolling waterfall spectrogram. That lets you see the signals so you are not endlessly scanning noise with your headphones. Different SDRs tend to have different useful features. The map uses colors: purple for KiwiSDR (with interesting frequencies already tagged), green for OpenWebRX (typically using an RTL-SDR receiver, which can get noisy but offers more custom functionality), and blue for WebSDR (only given to receivers that have high scientific or research value).

After selecting a few with good signal-to-noise ratio and visible activity across the HF band, start tuning into these well-known signals:

• UVB-76 (The Buzzer) - 4625 kHz, USB mode. A repeating buzzer that sounds like a ship's horn. Occasionally interrupted by a Russian voice.
• The Pip - 5448 kHz in daylight, 3756 kHz at night, USB. A repeating pip marker that also features occasional Russian speech.
• The Squeaky Wheel - 5367 kHz in daylight, 3363.5 kHz at night, USB. A two-tone high-pitched squeak that quickly becomes annoying.
• HFGCS - 11175, 8992, 4724, 15016 kHz, USB. US military HD voice-only traffic. Mostly silent, but when active, you hear cool transmissions.
• HM01 - 065, 9330, 10345, 11435, and 11530 kHz, AM (voice and digital data). A Cuban number station with voice groups in Spanish and number groups.
• E11 / Oblique - Varies by day: Mon–Wed 8102, 12630 kHz; Tue–Thu 12385, 13470 kHz; Fri–Sun 7850, 8680 kHz; USB. An English-speaking number station featuring a woman reading numbers and random phrases.
• WWV time signal - 2.5, 5, 10, 15, 20 MHz, AM. Spoken time and clock ticks from a US-based time station.
• CHU Canada - 3330, 7850, 14670 kHz, AM. A Canadian time station with spoken announcements.

The time stations are the boring ones, but they are good practice for spotting other interesting signals on the waterfall because they are consistently broadcasting. Once you know what a utility signal looks and sounds like, the genuinely weird signals stand out much more clearly.

Number stations are creepy because they are also really calm

A flat voice reading out codes is so much worse than beeps and static

Number stations are one of the radio topics where the real explanation is already weird enough without adding folklore. These are shortwave stations that typically broadcast formatted numbers, letters, and code groups in a calm voice that immediately sets off a feeling of unease in listeners. The common assumption is that these number stations are one-way messages for intelligence assets, but the actual contents are not publicly available because listeners do not have the corresponding pad or key to decode them.

It is not a futile hobby, though. Active stations like HM01 and E11 are worth chasing. HM01 mixes Spanish voice numbers with digital bursts of data, so it both sounds cool and looks great on the waterfall. E11, commonly known as Oblique, has more of that classic number-station feel, with English voices reading groups at scheduled times. The routine of it all is what makes it feel so creepy. Out there in the world, there exists a hidden infrastructure of intelligence that you have only seen one side of: weirdly calm voices sending coded numbers into the ionosphere while listeners wonder who, if anyone, is out there writing them down.

I totally get why people are fascinated by these weird shortwave signals

The real reward is separating the technical utility from the mystery

After spending a few evenings jumping between all the buzzers and military channels, keeping to the number station schedules, and finding some weird digital modes, it becomes clear how much respect is due to the operators who keep their receivers open for use. There is plenty of folklore around shortwave, from dead-hand stations to haunted frequencies. Organizations like Priyom do a fantastic job cataloging and detailing the schedules for anyone who wants to investigate and hear these signals firsthand.

For many, the active signals are far more interesting than the old legends. A station you can tune into from the comfort of your home is just way more compelling than reading about creepy recordings from decades ago. But the real fun (and creepy) part of it all is that these signals are still transmitting, still monitored, but only half-explained. The mystery continues, and anyone with an internet connection can join the hunt.

Source: MakeUseOf News