西安市业余无线电频率438.500在2到3个月前就遭受了这种信号的干扰，干扰是一些分立的竖线，基本上没有任何的模拟调制信号，而且更换了QTH也是相同的竖线，如图所示[upl-image-preview uuid=ab70bb29-f89d-43e5-9243-56b18b80a070 url=https://storage.hamcq.cn/2025-11-23/1763888230-650975-0a1224f2295c602aadf77f1df356f3de.jpg alt={TEXT?}]

这个信号占频宽约0.2MHz，快跟WFM差不多了，而且疑似由于杂散，这里还能收到西安北站对讲机的声音……

用别的设备也可以收到这种干扰吗？看这种波形应该只会导致 FM 接收机的静噪被打开，不会干扰到通联。

@"BI1XJT"#p87891 会的，而且干扰很严重，西安直频都跑到438.710上了

我也听到过。有一位HAM改到438.505，听到到效果还可以。。不过，还是改变频点到另外的位置比较好些

报给当地的无线电管理部门吧，测向应该可以找到干扰源的

持续时间多长？最好拍个视频

这是重复间隔大约5uS的脉冲，有可能是宽度调制

@"BI4OAE"#p87958 找了，他们找的当天干扰没开机

@"bg4uvr"#p87969 能不能仔细讲一下？因为我们目前测这些信号的不太了解这个

@"BD6MM"#p87960 [这里](https://www.kechuang.org/z/m/weu8bc?type=comment)

Help request: Does anyone recognize the modulation method of this signal?

BI9BUM

The amateur radio frequency of 438.500 MHz in Xi'an has been experiencing interference from this signal for about 2 to 3 months. The interference consists of isolated vertical lines, with virtually no analog modulation signals. Changing the QTH (location) also resulted in the same interference pattern, as shown in the image.

BI9BUM

This signal occupies a bandwidth of approximately 0.2 MHz, which is very close to WFM. Furthermore, it appears that due to scattering, I can also receive the voice from the Xi'an North Station walkie-talkie here…

BI1XJT

Can other devices also receive this interference? Based on the waveform, it should only cause the noise in an FM receiver to be activated, without interfering with the communication.

BI9BUM

BI1XJT Yes, and the interference is very severe; Xi'an Direct Frequency has even reached 438.710.

BG7NQF

I've also heard about that. One person switched to 438.505, and reported that it worked reasonably well. However, I still think it's better to change the frequency to a different location.

BI4OAE

Report this to your local radio management authority. They should be able to identify the source of the interference.

BI9BUM

BI4OAE I looked for them, but they didn't find it working on the same day.

BD6MM

How long does it last? It would be best to take a video.

BI9BUM

BD6MM Here

bg4uvr

This is a pulse with a repetition interval of approximately 5µs, which could potentially be a form of width modulation.

BI9BUM

bg4uvr Could you please explain this in more detail? We're not very familiar with how we should be measuring these signals.

bg4uvr

BI9BUM I'm also not very familiar with it; my guess is that it involves some kind of data transmission.😅

BI9BUM

I recently called a relevant department to inquire about this frequency, and they confirmed that it was not used in their primary business operations, so it must be interference.

seagulls

Is it arranged like this?

BD6JYO

First, manually determine the direction of the signal. Then, identify what kind of device is transmitting it. Assume it's a malfunctioning radio.

BI9BUM

BD6JYO They say it's simple to measure direction, but we've been doing it for several months now, and it still requires multiple signal measurements to determine the direction.

BD6JYO

BI9BUM This intermittent signal can be best measured using the FNJ directional antenna. If that's not possible, manual direction finding should be used, selecting multiple locations and recording the direction corresponding to each peak value.
If all else fails, use a more basic approach by identifying multiple points and starting with measurements from those locations. Then, gradually narrow the search area until you get closer to the target.

BI9BUM

BD6JYO I've successfully obtained the Doppler direction finder. Thank you. @BI9CLP I spent a lot of money on a surveying instrument, but according to FNJ, because I couldn't determine whether it was transmitting without a carrier signal, it might not work. In any case, I bought it now and will see how it performs later.

BD6JYO

Regarding this spectrum plot, I had previously recorded similar signal characteristics, which appeared to be...Shenhua MeiThe 8th default channel on the radio. Frequency: 438.495 MHz, Sub-audio DCS026. This unit exhibits significant dispersion even when viewed with an SDR; it has not yet been tested with a spectrum analyzer to measure the dispersion. Previously, another station discarded this unit during unified testing.
ThisShenhua MeiThe walkie-talkies have been approved, and the approval was for the frequency-tuned handheld device (for amateur use), with a specified power.<=5W, which may be between cost and reducing the filter in subsequent production.

BI9BUM

BD6JYO It shouldn't be a walkie-talkie. We counted the signal times, with a fixed transmission of 30 seconds, followed by a 40-second interval, then another 30-second transmission, and finally waiting for about 2 minutes and 20 seconds before repeating the cycle. Walkie-talkies don't have such precise timing.

BD6JYO

BI9BUM 只要有一个固定频率的峰值就相当于有载波了，比如各种FSK，从sdr上来看用FNJ测向没问题
另外这种频谱特别大的要考虑下杂散，可以试试上下调一下频率看能不能找到基准频率数传一般在400至510MHz中间

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