Earlier quoted context omitted.
You can be using a device and it might not harm you personally, but it could harm anyone around you using these frequencies. This includes airplanes and ground control, and boats. Your device's interference could cause problems or even life threatening dangerous situations. That's why it's illegal in many countries to cause too much radio interference (there's always some).
> but it could harm anyone around you using these frequencies. Not really. Part of the FCC certification process is that devices need to accept interference from other devices operating within the limits. Go read the FCC sticker on the bottom of any nearby device if you don’t believe me. It’s spelled out in the text. The only reason the author had a problem is they put it right next to, quite literally, a highly sens…
Note that only some classes of device have this requirement to accept all interference from devices operating within the limits. For some classes of devices if a consumer device interferes with then the consumer device's owner is responsible for stopping the interference even if the consumer device is operating entirely within limits.
The FCC regulations are divided into several parts, covering different devices and services. For example Part 87 covers various aviation radio services and devices, Part 97 covers Amateur Radio, and Part 20 covers mobile phones.
For any given frequency there might be devices or services covered under several different parts that can radiate on that frequency. There will generally be some kind of hierarchy among them where devices are not allowed to interfere with devices higher in the hierarchy and must accept interference from devices higher in the hierarchy.
The Part that covers much of consumer electronics other than mobile phones is Part 15. For most common consumer devices, if it is not a mobile phone and you did not need to get a license from the FCC to use it it probably falls under Part 15. This includes "intentional radiators", which are devices that are intended to emit radio such as WiFi routers, "unintentional radiators", which are devices that intentionally generate radio frequency energy within the device but it is meant to stay within wires or within the device, and "incidental radiators", which are devices that aren't intended to generate radio frequency energy but do so as a side effect such as DC motors and mechanical light switches.
Part 15 is at the bottom of the hierarchy.
For Part 15 devices, 47 CFR 15.5(b) says:
> Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by industrial, scientific and medical (ISM) equipment, or by an incidental radiator.
Other Parts can have quite different rules. For example Part 95 Subpart C, which covers radio control such as is commonly used in RC models, says this:
> (a) RCRS stations must not cause interference to:
> (1) Authorized radio operations in the 72–76 MHz band, including radio remote control of industrial equipment on the same or adjacent channels; or,
> (2) Broadcast television reception on TV Channels 4 or 5.
> (b) RCRS operations are not afforded protection from interference caused by the operation of:
> (1) Industrial, scientific or medical devices (see part 18 of this chapter) operating in the 26–28 MHz band; and,
> (2) Fixed and mobile stations in other services operating on the same or adjacent channels.
For Amateur ("ham") Radio, the interference rules are much more extensive, because hams are authorized to use a lot of frequency bands that overlap other services. Here's a link if anyone is curious [1].