Could you please identify this signal?

BI9BUM

如图：

该信号自2025年9月出现，截至今日仍在持续发射，此信号每两条竖线间间隔21KHz，偶有功率变化，带宽约0.4MHz，信号的其他信息随时间基本不变，每竖线间是连续的，应该不是跳频信号；
视频无法上传，信号可以打开对讲机静噪，听起来是类似大型电动机或水泥泵车工作时的声音，该干扰覆盖及其巨大，在宝鸡，渭南，西安等地都能收到，严重干扰业余通信，向西安监测站求助，监测站的工作人员协助利用固定站测向，发现位于西安高新区，但真当我们去了，却发现此处干扰信号强度较低，怀疑多径效应和山体反射导致。
现在我们自己测向，方向是几百公里外的彬县，永寿县，乾县，长武，甚至甘肃庆阳宁县，都有可能，如果有居住在以上地区的ham，能否帮忙监听一下是否有信号？如果有熟悉各种信号制式的ham，能否识别出此信号的类型等信息？非常感谢！

BG6HFD

Is there anything like LoRa or beacon signals around frequency 433?

BI9BUM

BG6HFD Directly at 438.5, not at 433.

BG6HFD

If there are many hills or large metal objects (such as substations, factories, and factory towers) near the signal source, the direction finding may be inaccurate. Based on the description, unless it is interference from a data transmission device, the 21 kHz interval also resembles the interference from a DC motor.
It might be worthwhile to focus on nearby factories and also consider whether there are similar interference signals in other frequency bands.

BI9BUM

BG6HFD He always fired for a fixed 30 seconds, but the interval between each firing was different.

BG9OWJ

This is the interference signal emitted by various electronic devices, which should be called electromagnetic leakage. According to this, it should be very weak and not cover such a large area. If you can receive it everywhere, its power would be extremely high, and the size of the signal you receive in different places should also vary significantly. For comparison, consider radio signals with power levels of several kilowatts, which have a coverage range of over 100 kilometers (radio frequencies are lower, so they propagate further), and the variations in strength received in different locations are also very noticeable.

BI9BUM

BG9OWJ There haven't been any significant changes. The signal is very unusual, and it's precisely at 438.5 kHz. I didn't find any similar signals on other frequencies (I initially suspected 219.25 kHz), but we measured a maximum of +20 dBμV. According to the measurements from the local monitoring station, the signal is about 13 dBμV at approximately 13 kilometers away, and about 10 dBμV at approximately 30 kilometers away.

BI9BUM

BG9OWJ Currently, it seems to be in the northern direction of Xi'an, but all the directional measurement stations are pointing southwest. I don't know why, and the southern Qinling Mountains are all mountains.

BG2EFX

Let's compare the signals from 433: they are all LoRa, but different forms of data transmission are also possible.

BI9BUM

BG2EFX It's different; 433 is very chaotic, while our pattern is very strong.

BI9BUM

BG2EFX The key issue is that I don't know what kind of modulation it uses, and even whether it's a form of data transmission is unclear.

BG9OWJ

If the duration of each transmission is the same, it's likely that some other object is transmitting interference. Check to see if it's synchronized with another signal.

BI9BUM

BG9OWJ Okay, I'll contact the relevant regulatory authority (No委) to inquire about this. Specifically, could a device with scattered transmission characteristics cover such a large area?

BG9OWJ

BI9BUM I don't think so. A main signal of a few kilowatts probably won't cover more than about 100 kilometers, and the scattered signals will only account for a very small portion of the total energy.

BloodBlade

Examples of this include switching power supplies and inverters. These devices, besides transmitting directly from the main unit, can also transmit along the power cable and ground wire, and then be emitted from a transformer or other location. This could mean that the interference source itself is not a single point.Furthermore, interference from the main body could also combine with standing wave effects to disrupt signal strength.

BloodBlade

BloodBlade It might also be worth considering the transmission frequency of a faulty radio device and the interference from your own power supply, combined through mixing. (Is this actually possible? I'm not sure.)

BD6JYO

I received one last year, but the test failed due to a short transmission time. This doesn't seem like a problem with a switching power supply, as switching power supplies have unstable oscillation frequencies and should be oscillating back and forth. There is also no fluctuation in power. I suspect it might be interference, so I could check nearby frequencies or multiples of the frequency.

BH8GIO

According to AI, it's a high-order harmonic drive for medium and high voltage AC variable frequency drives.
It might be caused by a nearby hydroelectric power plant.

BD6JYO

BH8GIO It's unlikely that power system harmonics would be so stable, and they wouldn't reach frequencies of hundreds of MHz.

BI9BUM

BD6JYO Yes, I even expect that this device might not be transmitting data, and I even suspect that it's a radar. However, the radar seems to transmit only once every 2 minutes, and each transmission lasts for about 30 seconds.

BI9BUM

BD6JYO 因为这东西发射时候信号强度还在变化，约5dBu左右，所以才想到可能是雷达

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