Unidentified sound on a CHU frequency

[GB46]

This morning, as well as other mornings, I hear this strange pulsating sound on 7850 kHz. It doesn't seem to be RFI, as it fades in and out. Sorry about the quality of the recording; my computer added a bit to the already high noise level when I connected it to the computer to record the sound. Please listen, instead, to the pulses as they fade in and out:

http://gbusch.altervista.org/temp/7850_kHz_1700_UTC.mp3

PS: The signal was a lot stronger until I decided to record it.

CHU's time signal itself can't be heard on that frequency here until the early evening hours. Does anyone know what I'm hearing?

 

[brickson98]

I heard the same thing earlier this afternoon on two KwikiSDR's accessed via sdr.hu. One located in northern Utah, near Salt Lake City, and another located in Idaho. Here's a sound clip. Sounds like the same sound to me. It was a very strong signal.

I don't hear anything on any SDR's now, though. It only seemed to be audible from the two I mentioned above. I listened for it on other SDR's located around central and eastern US, but I didn't try any others in the surrounding areas.

I see you're located in British Columbia, so it must've been from something around northwestern US, or southwestern Canada.

 

[GB46]

I heard the same thing earlier this afternoon on two KwikiSDR's accessed via sdr.hu. One located in northern Utah, near Salt Lake City, and another located in Idaho. Here's a sound clip. Sounds like the same sound to me. It was a very strong signal.

I don't hear anything on any SDR's now, though. It only seemed to be audible from the two I mentioned above. I listened for it on other SDR's located around central and eastern US, but I didn't try any others in the surrounding areas.

I see you're located in British Columbia, so it must've been from something around northwestern US, or southwestern Canada.

Thanks. Yes, that's exactly the sound I hear. Sometimes it has been strong enough to startle me when I have the audio gain up trying to hear CHU during unfavorable hours. That band is pretty good in the morning for Asian stations, but not for anything as east as Ottawa, CHU's location. The fact that it eventually grows a lot weaker and disappears altogether leads me to suspect that it isn't anywhere near me. I'm less than 40 km from the U.S. border, so Oregon, California, Utah or Idaho would seem more likely than, say, Washington State, although it may not even come from North America.

 

[krokus]

At first I figured it was a plasma display, but it sounds more like a version of an HF radar signal.

 

[GB46]

At first I figured it was a plasma display, but it sounds more like a version of an HF radar signal.

Your sound clip has the signal over WWV, while mine was on a CHU frequency, so time signals in both cases. I wonder what the significance of that is. Russia's woodpecker was something I heard very often during the '8os, and in many cases it was right on top of their own Radio Moscow, of all stations to interfere with!

 

[Haley]

Hearing it here in Central Iowa standing in my back yard on a sunny 40 degree day. Using a Skywave SSB off the whip, loud and clear over CHU on 7850.

 

[GB46]

Since this thread has a couple of good sound clips, I'll be removing mine from my webspace, as it's unrelated to my site's content, and I can no longer edit my original post.

 

[Token]

This sounds like it might be a Chinese radar. The rep rate and general sound is about right and they are often in the right frequency range. If you happen to be on an SDR a screen shot might help. What mode was the audio recording done in?

T!

 

[GB46]

This sounds like it might be a Chinese radar. The rep rate and general sound is about right and they are often in the right frequency range. If you happen to be on an SDR a screen shot might help. What mode was the audio recording done in?

T!

It was in AM mode, since I was trying to get CHU at the time. Switching to USB didn't change it much, except that it made the sound harder to hear. I don't have an SDR; I made the recording via a connection between the line-out jack on my R75 and the computer's line-in jack, using the Windows sound recorder. The result was converted from the Windows WMA format to MP3. An over-the-horizon radar seems quite possible, although I'm not sure if China uses that technique.

 

[brickson98]

This sounds like it might be a Chinese radar. The rep rate and general sound is about right and they are often in the right frequency range. If you happen to be on an SDR a screen shot might help. What mode was the audio recording done in?

T!

The sound is quite a bit different today. It's a slower sweeping sound rather than a fast buzzing sound. Here are a few sound clips that I recorded from multiple SDR's via sdr.hu. They are all AM at 7850KHz:
Stevensville, Montana - USA
Point Reyes, California - USA
Crooked River Ranch, Oregon - USA
(Unspecified city) Southern Nevada - USA
Corinne, Utah - USA
Weiser, Idaho - USA

I did not hear it on any SDR's I tried in or west of Denver, Colorado, or in or north of St. Paul, Alberta. I also tried SDR's southwest and southeast of the southern Nevada site, and could not hear it. The southwest one is located in Laguna Hills, California, and the southeast one is located in Sedona, Arizona. I also tried one in Prescott Valley, Arizona, and it was not heard either. Lastly, I tried multiple SDR's located around Seattle, Washington, and could not hear it there either.

So, either propagation is bouncing it right in the Oregon, Idaho, Utah, Nevada, California area, or it's located somewhere around there. If I have more time tonight, and the noise is still heard, I will check signal levels at each of the above mentioned SDR sites. Just a bit tricky when it's usually coming in with CHU.

Finally, I have a screenshots from the Corinne, Utah SDR and the Point Reyes, California SDR waterfalls. You can find them here.

 

[GB46]

Quite a different sound, but I haven't heard anything on 7850 today (not even CHU). This is likely due to bad propagation combined with the higher noise level I get here during a rain or snowstorm, the latter of which we're in right at the moment. Our nearby power lines seem to arc under those conditions.

 

[brickson98]

Quite a different sound, but I haven't heard anything on 7850 today (not even CHU). This is likely due to bad propagation combined with the higher noise level I get here during a rain or snowstorm, the latter of which we're in right at the moment. Our nearby power lines seem to arc under those conditions.

I wonder if these are two different sources of interference on the same frequency, or if they're involved with each other somehow. They both seem to have "radar like" sounds to them as far as I know.

Also, I only heard the sounds this morning, and when I went to check back shortly before 1800Z, it was gone. Which only pushes the propagation theory even further on this one. I'm really starting to feel like it is not coming from North America at all.

 

[brickson98]

Well, somebody's comment about China peaked my interest. So I went and checked out some Chinese based SDR's. I wasn't hearing anything, until I went to one based out of Hong Kong. I heard this. Sounds exactly like what I was hearing in the sound clips I posted above. I'm going to search around on SDR's in the area and see if I hear it anywhere else.

I know this isn't the same exact sound we were hearing before, but I have a feeling they're linked. If somebody doesn't feel the same way, I'll start a seperate thread on this "new" sound. Just seems too coincidental that they're both heard in the same areas, around the same time, on the same frequency.

 

[GB46]

Also, I only heard the sounds this morning, and when I went to check back shortly before 1800Z, it was gone. Which only pushes the propagation theory even further on this one. I'm really starting to feel like it is not coming from North America at all.

That's exactly what I was about to add until I read your comment. The fact that I've only heard it in the morning, and that most of what I hear on SW during those hours comes from Asia due to the sun's position, made me think the same way. The sound gradually fades out around the same time as the Asian stations.

 

[brickson98]

Well, I did some more listening on different SDR's around Hong Kong. So far I've heard it on an SDR in Talisay City, Philippines, and the strongest on an SDR in Kobe City, Japan. The links are to the recordings. The waterfalls for each are posted on imgur here. I'll post anything else I find as I keep going.

Edit: Just checked back on the SDR's in Japan, the Philippines, and Hong Kong, and I no longer hear it on any of them. So either the source is no longer transmitting, or it isn't located near there, and the signal faded in that region.

 

[krokus]

Some of the signals on the SDRs, seem more like plasma display RFI.

 

[brickson98]

Well, it seems to have faded out on every SDR I try a bit early today. I tried to find it again on different SDR's located around the world, but couldn't. I caught the slower noise I was hearing yesterday again. Heard it on an SDR in Novosibirsk, Russia. Here's the sound clip. I also heard it again on multiple SDR's in the same area of the US as yesterday, before the signal was lost. Still didn't hear the very fast "tapping" we originally heard. Here's a screenshot of the waterfall from the Russian SDR mentioned above.

This signal just seems to keep popping up all over the world. I still have no clue where it could be originating from. The only thoughts I have on its location is that it's not located in North America. I've heard it the strongest in Japan and eastern Russia so far.

 

[brickson98]

Some of the signals on the SDRs, seem more like plasma display RFI.

Just refreshed and saw your reply. I just don't think this many people would be using a plasma display in so many different locations, all at the same time. Also, I highly doubt the owners of at least one of the SDRs would place a plasma screen tv anywhere near their equipment, and it's apparently located in a slightly remote location, so there's shouldn't be any interference from neighbors, but I can't be 100% sure. They just give more information on what they're doing. The Northern Utah SDR. They have SDRs listed on sdr.hu and websdr.org.

But, again, it seems extremely unlikely that it's RFI from a plasma screen tv since I've checked multiple SDRs around the world, all within a few minutes of each other, and I doubt 4 people with SDRs from China, the Philippines, Japan, and Russia would all be using plasma screen tvs at the same time in the middle of the night for them. And, some of the people who have replied here have heard it on their own equipment.

Edit: Every video I can find on what plasma screen tv RFI sounds like does not sound like most of what I've shared from the SDRs. I can hear it's a similar sound to what we were originally hearing, but is missing the prominent "tapping" sound. These are the video examples I'm basing this off of: Video 1, Video 2, Video 3.

 

[Token]

OK, you have two different signals here. Yes, they may have been hitting the same frequency, 7850 kHz, on different days, but they are two different signals and probably unrelated.

They are both radar, but different kinds of radar.

The first is a typical Chinese BPSK coded radar at a fairly common rep rate for them, about 32.4 Hz. On lower frequencies they often use double that rate. These radars can (probably, the Chinese ain't really being specific) track ships and aircraft.

These kinds of radars move around in frequency, as needed, to leverage current propagation conditions. They are typically on many frequencies per day, and they may not be on the same frequency, or frequency set, every day.

The second appears to be CODAR or WERA radar, and there might be more than one radar in overlapping operation, both the sounds and your screen shots seem to indicate more than one source. This is an FMCW or IFMCW radar that chirps across a specific bandwidth at a specific moderate rate, they often are about 1 sweep per second, but they can be faster, or slower, than that. When you have more than one interleaved this can make it sound much faster. These radars are specialized coastal radars that typically monitor ocean wave and current activities.

T!

 

[Token]

An over-the-horizon radar seems quite possible, although I'm not sure if China uses that technique.

China has dozens of HF over the horizon radars, they are one of the most prolific users of HF radar. I have seen over 14 simultaneous Chinese HF radars in operation. They have several installations that use the specific mode heard in your first recording.

T!