Tech
FCC and receiver specs
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.