如图：[upl-image-preview uuid=1009b3e0-f957-4aa9-8850-825fdd288281 url=https://storage.hamcq.cn/2026-07-18/1784384838-255727-img-8754.jpg alt={TEXT?}] 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！

433附近么，是不是什么lora信号或者信标信号

@"BG6HFD"#p99481 直接就在438.5，没在433

如果信号源附近山体/大型金属物体多（变电站、厂房、工厂高塔等），测向可能不准确。看描述推测，要不是数传设备，但21kHz这样的间隔也有点像什么直流电机的干扰。也许要重点看看附近的工厂，同时也建议看看其它频段有无类似特征的干扰信号存在

这玩意就是各种电器设备发出来的干扰信号，应该叫电磁泄露吧。按理说应该是很小的，不应该这么大面积，如果到处都能收到，那它的功率将会非常惊人，而且你在不同地方收到的大小应该也有较大变化。参考一下广播信号，千瓦级别的功率，覆盖范围也就上百公里（广播频段更低，传播更远），而且不同地方接收到的强度变化也非常明显。

@"BG9OWJ"#p99487 基本没啥变化，非常离谱，不偏不倚刚好在438.5上，在其他频率（无委最开始怀疑219.25）也没找到一丁点信号类似这样的，最大就是+20dBμV我们自己测的，无委监测站测出来十几公里外是13左右，三十公里外差不多10左右

@"BG6HFD"#p99483 他每回发射就是固定三十秒，但每回发射的间隔不一样

@"BG9OWJ"#p99487 目前怀疑是在西安北边方向，但是测向站全测的朝西南，不知道为啥，南边秦岭全是山

对比一下433的信号一样就是LORA 不一样就是其他形式的数传

@"BG2EFX"#p99500 不一样，433很杂乱，我们这个规律非常强

@"BG2EFX"#p99500 关键不知道这是什么调制的，连是不是数传都说不来

Could you please identify this signal?

BI9BUM

For example:

This signal appeared in September 2025 and is still being transmitted as of today. The frequency between the two vertical lines is 21 kHz, with occasional variations in power. The bandwidth is approximately 0.4 MHz. Other information about the signal remains relatively constant over time. The signal consists of continuous transmissions between the vertical lines, so it is likely not a frequency-hopping signal.
The video could not be uploaded. The radio signal was active, but there was a lot of static noise. It sounded like the noise from a large engine or a concrete pump truck. This interference was widespread and could be heard in cities such as Baoji, Weinan, and Xi'an. It severely interfered with amateur communications. We contacted the monitoring station in Xi'an for assistance. The monitoring station personnel helped us use fixed-location directional finding to locate the source of the interference. However, when we went to the location identified by the monitoring station, which was in the High-Tech Zone of Xi'an, we found that the signal strength was relatively weak. We suspected that this was due to multipath effects and reflections from the mountains.
Currently, we are attempting to locate the source ourselves. The potential location is several hundred kilometers away, including Bin County, Yongshou County, Qian County, Changwu, and even Ning County in Qingyang, Gansu Province. If there are any amateur radio operators (hams) residing in these areas, could you please assist by monitoring for any signals? If you have experience with various signal types, could you identify the type of signal? Thank you very much!

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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