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.mp3Download MP3
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.
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.
EDIT: Updated the sound file to .mp3 format
4 hours later, the transmission is still ongoing. Much weaker signals though:
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?
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!
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 ....
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= )
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.
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.