Curiosity Collection of VLF Signals and Interferers (EP182)

追加: 2026-05-11

[00:00:06]Some radio signals sound really strange.

[00:00:13]Today I'm trying to explain some from my curiosity collection.

[00:00:23][music] Some are man-made, some originate in the atmosphere of our earth, and some are remaining a mystery to me. There are buzzing sounds, chirps, rhythmic clicks, and sometimes ghostly voices that piqued my curiosity.

[00:00:49]Today, I'm sharing my modest collection, and I'm looking forward to your comments.

[00:01:02]particularly curious. Some signals don't even physically exist in the air.

[00:01:16]The giants in the VLF range can be received anywhere in the world at any time of day.

[00:01:24]Their signals originate from enormous transmitters consuming a small town's electricity and radiating around 1 megawatt RF power.

[00:01:37]In this low data rate example, individual data bits are visible in the spectrum.

[00:01:46]Modern submarine communication usually applies FSK modulation with higher bit rate. They sound like mechanical noise and they are looking like [clears throat] garlands in a waterfall diagram. We are facing cryptic signals.

[00:02:05]Trying to decipher the information would be pointless.

[00:02:10]GQT is an English station in Skeleton.

[00:02:14]HWU transmits from France.

[00:02:18]DH38 from Germany and NAA from Cutler in the US.

[00:02:26]Further down the spectrum, I was able to receive the Australian station NWC hold.

[00:02:35]It's remarkable receiving signals from 13,000 kilometers distance with my indoor loop.

[00:02:45]Another important application is longwave radio navigation and due to its robustness, it's still used by ships and aircraft to complement GPS.

[00:02:58]The Russian Alpha system is operating for decades. You can still receive it worldwide with a good VLF antenna.

[00:03:08]The principle works with a sequence of three signals on different frequencies transmitted from known locations.

[00:03:18]Hyperolas on a map are indicating a specific time delay between two signals.

[00:03:26]Measuring the delay between blue and red signals, the receiver identifies on which of the yellow hyperolas it is on.

[00:03:37]From the delay between blue and green signals, it's deriving on which of the green hyperolas it is on.

[00:03:46]The intersection is its own geographical position.

[00:03:52]In the 190 to 535 kohz range, there are hundreds of similar systems worldwide.

[00:04:03][music] Time signals are serving hundreds of millions of radiocontrolled clocks.

[00:04:12][music] My local time signal arrives strong because the station is only 150 kilometers away.

[00:04:22]It appears there's only bits for the second, but in reality they are additionally transmitting the date, for example, encoded in the length of the beeps.

[00:04:35]The station near Moscow is apparently using sidebands to send additional information.

[00:04:45]Time signals are found on many frequencies, often transmitting a precise reference frequency.

[00:04:59]It's used for demand side management to switch street lights on and off for example.

[00:05:07]We hear it and we can see the wider signal in the spectrum. Control technology is transmitting more information.

[00:05:17]By the way, I'm achieving this crystalclear reception with a simple homemade loop, even though my location isn't particularly favorable.

[00:05:28]If you're interested, I recommend watching our earlier videos where we are explaining how to build them.

[00:05:40]The German maritime weather service on 147.3 kohertz is transmitting RTY text messages.

[00:05:58]And this station is a military one and is currently only transmitting its call sign.

[00:06:05]By the way, you can find smartphone apps to decode Morse code and RTY signals.

[00:06:15][music] My personal favorite is the historic station SAQ Grimmittton. It's only transmitting once or twice a year on special occasions and it's not easy to receive since it's effective radiating power is relatively low. You need a proper VLF antenna to receive it.

[00:06:43]My tip for VLF listeners in Europe, try to receive the alpha as well. Then your antenna sensitivity will be sufficient for SAQ crematin.

[00:07:00]This chirping is man-made.

[00:07:04]Scientific measurements are going on here investigating wave propagation conditions and the state of the ionosphere.

[00:07:15]You can imagine the method like this.

[00:07:20]Signal drops are occurring due to the superp position of ground and sky wave.

[00:07:27]Their location depends on the radio frequency and on the height of the reflecting ionospheric layer.

[00:07:36]While varying transmit frequency, these dips are moving back and forth causing signal fluctuations at the receive station.

[00:07:48]Applying some math, you can derive the state of the yonosphere from it.

[00:07:57]Covering the entire spectrum, you can hear their crackles on long, medium, and short wave bands.

[00:08:06]Electromagnetic pulses caused by lightning strikes can be received over long distances, especially on low frequency.

[00:08:27]It's the strongest event of this kind I've seen so far. Like on science fiction, solar wind is causing broadband noise in the atmosphere, massively disrupting VLF radio communications.

[00:08:43]This event caused no damage, but there have been stronger ones destroying even electrical power transformers.

[00:08:55]Noise from a solar storm I also found in the LF range.

[00:09:07]I'm provoking it by bringing the devices close to the antenna.

[00:09:12]Besides, its processor clocks, my PC's trackpad is causing interference, and its power supply is causing this red hump.

[00:09:24]At lower frequencies, every electronic device is a potential source of interference. and the strongest are usually close.

[00:09:37]It's often coupling directly via connecting cables such as USB or the power supply.

[00:09:45]We explained preventive measures in earlier videos.

[00:09:53]Comb signals with 50 or 60 Hz spacing are caused by mixing a switching frequency with mains harmonics.

[00:10:03]Suspect devices are those rectifying or switching mains voltage such as LED bulbs, motors, and power supplies.

[00:10:17]That strong 40 kHz signal was driving me crazy to find its source. Finally, I determined the inductive charger of an electric toothbrush. [music] This is our vacuum cleaner along with the alphas. Almost a work of art, isn't it?

[00:10:43]Even though it sounds like a time signal, it's the inductive cooktop in our kitchen. Its fundamental frequency is 75 kohz and harmonics are visible at exactly 2, three, and four times that frequency.

[00:11:01]Switching off the gremlin and skipping lunch is not an option. [clears throat] Instead, moving the antenna a few meters further away is also helping.

[00:11:15]Next, things are getting a bit mysterious.

[00:11:20]Normally, I would say they are lightning flashes, but the crackles regularity suggests they are rather strong man-made electromagnetic pulses.

[00:11:35]I have no idea what is causing this 20 kohz signal.

[00:11:44]This one is strange because it's maintaining a certain bandwidth while varying in frequency.

[00:11:56]Its spectrum indicates that it's constantly changing its switching frequency. I haven't identified it either.

[00:12:09]This bubbling sounds strange. Perhaps it's a narrow band chirp.

[00:12:17]Now things are getting really weird. No question, my receiver definitely shows a signal at 12.5 kz.

[00:12:29]It appears while I'm simultaneously pressing the transmit button on two PMR radios.

[00:12:39]Actually they are transmitting at 446 MGHertz which is far outside my receive band. 12.5 kohertz however are corresponding exactly to the difference of my transmit channels. The signal is not physically existing in the air. It's caused by nonlinearities in my receiver when the PMR devices are close.

[00:13:09]Among countless interm modulation products, this one is falling into my receive band.

[00:13:17]Now imagine broadband interfering signals. These would drastically raise my noise floor.

[00:13:27]Loop antennas are more resilient to intermods since they don't receive signals across a wide bandwidth like dipoles.

[00:13:39]There's more to it than listening broadcast. Hope you enjoyed my curiosity collection. Perhaps my example will help you track down and fight interference.

[00:13:52]Let me know in the comments. Just as a heads up, we computed signal predictions for VLF and LF.

[00:14:02]If you enjoyed the video, please give it a thumbs up. Thanks for watching. See you next time.