As hams, we are aware—or should be aware—of the spectral purity requirements spelled out in the Part 97 rules (§ 97.307). The purpose of these rules is to prevent unintentional interference. Well, as the recent brouhaha over the 5G rollout here in the United States has pointed out, it’s not just about transmitters.
In a word, the airlines were upset about the 5G rollout, especially near airports, because they contended that 5G transmissions in the 3.7 to 3.98 GHz band could possibly interfere with aircraft altimeters receiving signals in the 4.2 to 4.4 GHz band. The FAA have said aircraft at 50 U.S. airports might possibly be vulnerable to this interference.
There’s a good explanation of this situation here, but the crux of the matter is that the altimeter receivers weren’t designed with enough filtering to reject the 5G signals. The airlines could replace those altimeters with newer ones with better filtering, but that’s expensive and takes time. Hence, the conflict between the airlines and cell providers.
So, in order to avoid this kind of thing from happening in the future, new FCC Chairwoman Jessica Rosenworcel is planning to launch a Notice of Inquiry (NOI) that would try to determine what, if any, rules are needed for radio receivers to ensure that services occupying adjoining frequency allocations don’t interfere with one another. An Urgent Communications article reports that this NOI may get underway as early as April. The article quotes Rosenworcel as saying, “We face a hard truth. Greenfield spectrum—open and cleared for use—will not be as simple or easy to find. We will have to invest in new technologies to promote efficiency and use a range of spectrum policy tools, including shared access, priority and preemption, lightweight leasing, and dynamic database coordination to ensure access to our airwaves.”
She also noted, “This inquiry would ask how receiver improvements could provide greater opportunities for access to spectrum. It would explore how these specifications could come in the form of incentives, guidelines, or regulatory requirements—in specific frequency bands or across all bands. And it would seek comment on legal authority and market-based mechanisms that could help create a more transparent and predictable radiofrequency environment for all spectrum users—new and old.”
So, while the current focus is on the 5G/FAA situation, be aware that this will affect amateur radio sometime in the future.
EU already has this. Receivers are expected to be state of the art, and they should be able to operate in a hostile environment, where adjacent frequencies are occupied.
Frankly, this sort of thing is way overdue for the US and other areas. As radio amateurs we spend a lot of thought and time over designing/building/buying radios that have superior front ends, to reject all the garbage that’s out there.
Now, what’s sauce for the goose is sauce for the gander. Transmitters must also clean up their act, since dumping garbage in another receiver’s passband is never a win-win situation.