Originally published on the WeChat public account "对讲机世界" (Dianchu Ji Shi Jie)Original link:
Purpose of reprinting: To comply with radio management regulations, protect the rights of one's legitimate radio station, and to combat illegal stations. Respect life, and avoid using handheld radios or other prohibited transmitting devices in situations where their use is not permitted.
This article is submitted by a hobby radio enthusiast: Hello everyone, I am BA7XXX (the last three digits are not disclosed), and recently, while browsing some materials, I discovered that the secondary emissions of 430MHz handheld radios can seriously interfere with certain companies' wireless monitoring devices. The two images below are from the relevant pages of the user manual for this wireless monitoring device, which we can see requires a frequency range of 863～930MHz. Dividing both ends of the frequency range by 2 gives us: 863/2=431.5MHz to 930/2=465MHz. This means that it may interfere with handheld radios operating in the nearby frequency range of 431.5～465MHz, causing secondary emissions interference. Because for most transmitters, it is difficult to completely eliminate secondary emissions; we can only say that they meet specific standards, such as Class A standards. When this wireless monitoring system receives secondary emission strength from nearby handheld radios (such as security radios) greater than the signal strength of the useful signal, interference will occur, manifesting as packet loss and errors. If at this time, a physiological alarm signal occurs, it will delay the transmission of the alarm signal, leading to a delayed rescue opportunity.
In addition to interference from second harmonic emissions, it may also be interfered with by the 800 MHz digital cluster (ranging from 870 MHz), as well as by GSM-R systems used on railways (refer to the "Two Way Radio World" article: "Frequency Planning and Characteristics of Railway GSM-R"). Therefore, even if we do not consider the frequency requirements for biomedical remote monitoring devices in the latest version of the "Technical Requirements for Low Power Short Range Wireless Transmission Equipment" (the closest allowable frequency range is 608～630 MHz), it can still be interfered with by legally established radio stations, which can also cause important physiological alarm signals to be delayed or not transmitted in a timely manner, delaying rescue efforts.
Considering the specific use case and compliance requirements, since wireless remote monitoring devices fall under the category of biomedical remote monitoring equipment as described above, and the 86-930 MHz range mentioned in the manual does not fall within the aforementioned technical requirements (as shown in the figure), it is therefore non-compliant from a regulatory perspective.
Perhaps it's because the maximum transmission power is small (only 0.1W) and it's used internally, so there hasn't been any obvious external interference (i.e., it may be difficult to detect outside the hospital). This allows for a situation where "no one reports, no action is taken." Finally, the article states: This discussion is not directed at any company. Screenshots from the instructions can be blurred, and we call on the industry to pay attention to frequency planning and guide proper, legal use of frequencies. Reducing harmful interference and protecting lives are important! Based on my analysis above, can you explain these risks from a technical perspective? This is very important for public safety!
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