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Strange sounding transmission on 7156 kHz

I keep hearing these transmissions from time to time, turning up on different frequencies. Today its on 7156 kHz. It goes on for quite some time. Does anyone know what they are?

Strange sounds 70156kHz

.mp3

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11 comments

11 Comments

LarryDee

Oct 19, 2022

This sounds oddly like a switched power supply charger. I have an Anchor phone charger that puts out horrendous interference that sounds exactly the same except for the pauses.

coildog

Oct 20, 2022

Replying to

Yeah, I know what you mean. My LED table light adds to the chorus as well. Fortunately, the plasma TV sets seem to be gone. My neighbour owned one, it was really bad. Technology marches on!

@qrp-gaijin:

Are you a registrerd user at hfunderground? If so, feel free to post the chip-chip-chip sound on the forum. Maybe someone know what it is?

qrp-gaijin

Oct 20, 2022

Replying to

Actually no, I'm not a registered user at hfunderground, so I can't post there. I hope you find out what your unknown signal is! But I would suggest using a very small loop antenna for direction finding, to at least rule out the possibility that it is coming from a local source (like a switched-mode power supply). I'm no expert in direction finding, but I guess that with a very small loop antenna and a portable receiver, you can walk around outside and try to null out the signal with the loop, which will give you a rough idea of its bearing (but see note below about skywave signals). Then you can change your position by say 5 meters and try again. If the bearing of the signal changes significantly, that might be a strong clue that the source of the signal is nearby. If the bearing doesn't change when you change your position, that may be a clue that the signal is distant in origin.

A general problem with using normal small loops for direction finding is that the null of a small loop is only effective on vertically-polarized signals. Nearby signals will likely be vertically polarized. But skywave signals that bounce off the ionosphere will have their polarization randomized and will have some random horizontal polarization component in addition to the original vertical polarization component. This horizontal polarization component, unfortunately, will be detectable in the null of a small loop, because the null for vertically-polarized signals is actually the lobe (maximum) for horizontally polarized signals! And depending on the random polarization due to ionospheric bounces, there will be a random amount of horizontal polarization added to the signal, and so there will be a random amount of "filling in" of the null in the loop antenna, which in turn can cause the null (minimum signal direction) of the antenna to appear to be at a different bearing, where both the vertically-polarized and horizontally-polarized signals are at a minimum. But due to the time-varying amount of horizontal polarization, the amount of "filling in" of the "real" (vertically-polarized) null, and hence the apparent null direction, will change over time, making nulling out of (and direction finding of) skywave signals difficult.

The Coplanar Twin Loop antenna (https://web.archive.org/web/20201218104743/http://theradioboard.com/rb/download/villard_co-planar.pdf) has a null that minimizes both vertically-polarized and horizontally-polarized signals, and such a null can be used for more accurate direction finding of (or nulling out of) skywave signals. The null is also unidirectional.

(By the way, the above explanation of the CTL antenna's operation is my interpretation of the above-linked CTL article. My interpretation may be wrong -- in addition to the effects of horizontal polarization, the article also mentions vertical angle of arrival as being another factor causing "filling in" of the null on a traditional loop antenna, which I don't fully understand. Any discussion would be welcomed!)

coildog

Oct 21, 2022

Replying to

Thank you for the detailed description about direction finding. Direction finding seems to not only involve some equipment, but also understanding. I fear I might fall a bit short on both of those requirements!

My loop project didn't work out the way I had hoped. I could not get the sensitivity I had hoped for. Especially at lower SW frequencies. I did not get arounnd to trying the regenerative approch that you kindly linked to. The circuit appeared very appealing though. I have saved it for another potential project later on. There is SO much to try and do!

Sorry about the hfunderground, I got the impresson you were active there. But never mind, I might register there myself. Though I was a bit puzzeled by all the GDPR rules on the board. There seemed to be no limits to what they could use the information the userdata for.

Regarding the vertical incidence angle of radio waves ... I have noticed, when playing with ferrite antennas on LW, that I don't get a total null just by rotating the antenna horisontally. To achieve a total null, I also have to tilt the antenna at a vertical angle, maybe 10 to 20 degrees. The radio waves appear to be 'falling' in, almost like rain in a strong wind. I guess that makes sense in a way, the ground absorbs radio waves.

coildog

Oct 18, 2022

Well, I got lucky! I found a transmission on 7160kHz with strong signals. This time I recorded it with an SSB receiver. Hope the recording makes more sense this time.

chip-chip-chip-signal_7160kHz_SSB-mode_18oct2022_1609UTC_Nort_Norway

.mp3

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EDIT: Updated the sound file to .mp3 format

Update:

4 hours later, the transmission is still ongoing. Much weaker signals though:

chip-chip-chip-signal_7160kHz_SSB-mode_18oct2022_2056UTC_Nort_Norway

.mp3

Download MP3

This time I get a sense that there are two stations involved, and that the 'chip' sounds may be 'ack'- signals and the 'rash'-sounds are data. Does that make sense?

coildog

Oct 18, 2022

Thank you all for comments and information. Much appreciated! I've been checking now and then, but I've not happened on the transmission again. I will try and get a better recording next time it turns up.

@qrp-gaijin: The hfunderground seems to be a very interesting resource. I'll keep it on my list of useful sites!

w5jag

Oct 13, 2022

I've not heard anything like that.

As an aside, I have a SteppIR at my main QTH, and once you have used one at your QTH, you learn where to set it so it is on frequency with a low VSWR - as an example, in my installation, i set the antenna about 20 KHz high on twenty meters. There is a way to precisely calibrate the antenna to a particular installation, but it's a lot of trouble and I'm lazy.

They are fantastic antennas. I highly recommend them. It is so cool to push a button and instantly reverse the antenna 180 degrees to listen for long path and compare it to short path. I usually keep mine in bidirectional mode and point it at Europe / Australia with gain in both directions at the same time ....

73,

Win W5JAG

qrp-gaijin

Oct 13, 2022

I checked on the Signal Identification (SigID) wiki page at https://www.sigidwiki.com/wiki/HF but unfortunately didn't find anything that matched exactly the sound of the file you posted. But, maybe that page can give you some ideas.

The following forum seems to be active and dedicated to discussing unknown signals. Maybe you can get some more information there. https://www.hfunderground.com/board/index.php/board,27.0.html

I'm not sure, but it might barely be possible to use a small, directional loop antenna (in a clear area) for direction finding, so that you could get a rough idea of the direction from which the signal is coming. A phased loop+whip (or something similar like the Coplanar Twin Loop Antenna, the CTL, by the late Dr. Villard) would give a unidirectional cardioid pattern to differentiate between front and back (as opposed to the symmetrical figure-8 pattern of a small loop). You have to be careful about interpreting the direction of the signal origin due to the signal bouncing off of the ionosphere, but I think that Villard explained a little about this in several old research papers -- it's confusing stuff, dealing with the polarization of signals, how the polarization can be used in a loop+whip to get a unidirectional response, and how polarization gets randomized when the signal bounces off of the ionosphere. My vague memory is that in spite of the polarization randomization due to ionospheric bounces, there is still some useful information about the direction of the signal origin that can be inferred from a unidirectional antenna (like the CTL or a loop+whip) if we make some assumptions about the path of the signal taking the shortest path from the sender to the receiver, or something like that. Like I said, confusing stuff.

Villard's interest was in interference-canceling antennas that could null out a jamming signal coming from a particular direction, while allowing all other signals from all other directions to pass, thus allowing reception of the jammed signal. If there's interest, I may be able to find some old links to Villard's old papers. (EDIT: some links are in my old post on the CTL here: https://groups.io/g/loopantennas/topic/how_does_this_unidirectional/71488042?p= )

LarryDee

Oct 18, 2022

Replying to

This is amazing stuff. Makes for a great hobby just finding weird signals.

coildog

Oct 12, 2022

I've heard this type of transmission several times on different frequencies between 6 and 8 MHz. It sounds very rythmic so I am thinking it might be some kind of digital mode with ''handshake''. Getting curious to know what it is.

By the way, thank you for telling me about ANZA net, https://anzadx.net/ I didn't know. That was quite interesting.

LarryDee

Oct 12, 2022

Found this from a decade ago, could be the same thing. Amateur Radio VK4LC VK2KN orotdnSpes8400fi,796f6J 7i m1a78003139u70i2a03216u8tfi6megin ·

Was happily talking to a few US stations on 7.156Mhz last night when a big signal came up at just over +20dB on the S-meter here. Sounded very much like someone tuning their antenna/amplifier to me. After going clear with the US stations, a VK4 started talking to them and then VK1TX kept calling over people to contact the US stations with his StepperIR with a signal of....... well, you can take a guess. Now, I wonder who would have been tuning their StepperIR on the same frequency a minute or two before?? Typical ANZA net operator.... they just do as they wish. Listen on 14.183 to hear them exchange signal reports and find nothing out about who they're talking to.