Unidentified sound on a CHU frequency

brickson98

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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!
Thanks for the info! You'd think people would try to avoid interference a bit better than that considering CHU is always on that frequency.

On the bright side, I guess we can consider this mystery solved!
 

Token

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I took a look at 7850 kHz this morning, there are indeed several (5 or 6 that I saw) CODAR hammering around that frequency, basically from 7800 to 8000 kHz (and later saw another one around 8200 kHz). In general with these specific kinds of radars the lower the frequency the longer the intended range of operation. 4-5 MHz is long range, ~12 - 16 MHz is medium range, and above ~24 MHz is short range. ~8 MHz would be between the normal long and medium range bands, however the swept width, about 30 kHz, would seem to point to them being used in the long range application. The swept width of these signals can be used to calculate the range cell of the system, the narrower the swept width the larger the range cell. Long range systems typically have worse (wider) range cells while shorter range systems, with their wider sweeps, typically have better (narrower) range cells.

At a guess, based on the odd frequencies, these are Pacific or Asian sourced CODAR, but that is a total guess. I suppose they could be Central or South American also. They would not be US based, I am pretty sure that frequency range is not authorized for CODAR. I don't think they would be Canadian, I think Canada authorizes freqs for CODAR in about the same ranges as the US.

T!
 
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Token

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Let me clarify a bit (enter the sound of back-peddling). I said these were CODAR that I saw this morning, I should have said they were "CODAR like". CODAR is a specific type of radar, and I have no way of confirming these are indeed CODARs, however they are transmitting a signal that is near identical to CODAR and WERA. The more I watch these the more I think they might be Chinese, for example I just saw one stop on 7850 kHz (where it had been operating for hours) and jump to 7160 kHz, in the ham 40 meter band, it ran there for a couple of minutes then it stopped and went back to 7850 kHz, and a short time later it shifted to 7720 kHz. This is a very Chinese like disregard for the 40 meter ham band. However CODAR most typically does not frequency hop like that.

So these could be CODAR / WERA, or they could be another radar that has a very similar waveform. In general the performance of the radar is tied to the waveform used, and similar waveforms most often indicate similar tasking, so it is quite possible that two different radars that share the same waveform may, possibly, have the same or similar functions.

So a more accurate description would be CODAR like, if not CODAR, and possibly performing the same kind of work as CODAR.

T!
 

GB46

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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!
Then I'm guessing that's where the sound is coming from considering that I hear mostly Asian stations at that time of day .

What may or may not be related is a steady tone over WWV's 10 mHz signal heard right now at 19:00 UTC. It's a heterodyne over WWV's signal, and always present, even during the periods when WWV only sends the clock-ticking sound without a tone. If I use a narrow IF filter combined with the auto notch feature and adjust the twin PBT, I can get rid of most, but not all of the heterodyne, so the signal must be very close to 10 mHz. This has been going on for at least 30 minutes. I can't hear WWV on its other frequencies at the moment, so I can't tell if they're getting interfered with, as well.

At any rate, I've shut off my other electronic devices to see if they're causing this, but they're not, and the signal can also be heard on my portable with just the whip.

Strange that time signals seem to be targets lately!
 

GB46

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What may or may not be related is a steady tone over WWV's 10 mHz signal heard right now at 19:00 UTC. It's a heterodyne over WWV's signal, and always present, even during the periods when WWV only sends the clock-ticking sound without a tone. If I use a narrow IF filter combined with the auto notch feature and adjust the twin PBT, I can get rid of most, but not all of the heterodyne, so the signal must be very close to 10 mHz. This has been going on for at least 30 minutes. I can't hear WWV on its other frequencies at the moment, so I can't tell if they're getting interfered with, as well.

At any rate, I've shut off my other electronic devices to see if they're causing this, but they're not, and the signal can also be heard on my portable with just the whip.

Strange that time signals seem to be targets lately!
This is a sample of WWV recorded at 21:44 UTC. I'm using the narrowest IF filters I can select for AM from the stock filters on my R75, as I haven't added any optional ones, plus a tuning step of 1 Hz:


The recording starts at 9999.999 kHz. Note that the interfering tone is not from WWV itself. I then tune gradually upward, passing 10000.0 kHz and reaching 10001 kHz, at which point you'll hear the interference disappear. I then tune down again to 9999.999, where the interfering signal is the strongest.

The interfering signal is fading, so it can't be in my vicinity.
 

brickson98

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This is a sample of WWV recorded at 21:44 UTC. I'm using the narrowest IF filters I can select for AM from the stock filters on my R75, as I haven't added any optional ones, plus a tuning step of 1 Hz:


The recording starts at 9999.999 kHz. Note that the interfering tone is not from WWV itself. I then tune gradually upward, passing 10000.0 kHz and reaching 10001 kHz, at which point you'll hear the interference disappear. I then tune down again to 9999.999, where the interfering signal is the strongest.

The interfering signal is fading, so it can't be in my vicinity.
Have you heard the signal since you last posted? I'm curious as to what that one might be as well.

But going back to the old radar on 7850 KHz, it's coming in very loud on the Northern Utah SDR today. I can barely hear CHU in there with it. It's covering the band from roughly 7806 KHz to 7862 KHz. I suppose that's a sign propagation is decent right now. Here's a sound clip. And here's a waterfall screen shot.

Also, I noticed something I didn't notice before, but I also might've just missed it before. I forgot if anybody mentioned it before, and I just thought it's a detail that might be able to give more specifics on what it really is, even though we're pretty sure it's a CODAR equivalent. Every couple minutes, it stops, makes a higher pitched buzz, then continues. I have a screenshot here, and an audio clip here.
 

Token

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But going back to the old radar on 7850 KHz, it's coming in very loud on the Northern Utah SDR today. I can barely hear CHU in there with it. It's covering the band from roughly 7806 KHz to 7862 KHz. I suppose that's a sign propagation is decent right now. Here's a sound clip. And here's a waterfall screen shot.

Also, I noticed something I didn't notice before, but I also might've just missed it before. I forgot if anybody mentioned it before, and I just thought it's a detail that might be able to give more specifics on what it really is, even though we're pretty sure it's a CODAR equivalent. Every couple minutes, it stops, makes a higher pitched buzz, then continues. I have a screenshot here, and an audio clip here.
To clarify, two different radars were heard and described (a couple days apart) in the original questions in this thread. One was CODAR like, the other was not. The one in your screen shots and recordings is the other one, the not CODAR like radar.

The radar in your screen shots and recordings is Chinese. It may be one of the Chinese purchased Russian Sunflower-E radars, there is some indication that this is their waveform, but I am not sure of that.

Yes, the periodic change in the radar you saw, the change in pitch for a short duration and then return to original pitch, is a regular feature with those radars.

I see the CODAR like radar hitting CHU on 7850 kHz almost every day, sometimes right on the frequency, sometimes a few 10's of kHz off. I often see 3 or 4 copies of the same kind of radar in the same general frequency range. Typically I do not see the other, buzzing, radar hitting that frequency range, although occasionally it does.

T!
 

brickson98

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To clarify, two different radars were heard and described (a couple days apart) in the original questions in this thread. One was CODAR like, the other was not. The one in your screen shots and recordings is the other one, the not CODAR like radar.

The radar in your screen shots and recordings is Chinese. It may be one of the Chinese purchased Russian Sunflower-E radars, there is some indication that this is their waveform, but I am not sure of that.

Yes, the periodic change in the radar you saw, the change in pitch for a short duration and then return to original pitch, is a regular feature with those radars.

I see the CODAR like radar hitting CHU on 7850 kHz almost every day, sometimes right on the frequency, sometimes a few 10's of kHz off. I often see 3 or 4 copies of the same kind of radar in the same general frequency range. Typically I do not see the other, buzzing, radar hitting that frequency range, although occasionally it does.

T!
Ohhh, okay. I got them mixed up.
 

GB46

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I've heard it nearly every morning since then, and sometimes during the afternoon. I just got up, but I'll get back to you once I get the chance to check for it again this morning.
OK, I'm hearing it now at 17:30 UTC. When I tune far enough away from WWV the tone is modulation of a separate AM carrier (I'm listening in AM mode, of course), not a heterodyne with WWV.. As I mentioned earlier, the carrier is fading in and out rather rapidly, so it's not local interference. Anyway, it sounds no different from the audio clip in my initial report.
 
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