Section 11.2: Spectrum and Station Sites #

Where you put a station, and who else uses its band, can change how you may operate. A repeater may share its frequencies with radar, a home may sit near a protected receiver, and an antenna may rise near an airport. Check those conditions before treating a band allocation as the whole answer.

Who Else Uses the Frequency? #

On 70 centimeters, amateurs are a secondary service, sharing the band with government radiolocation (radar) systems. A repeater can stay within its amateur allocation and still interfere with one of them. As the secondary user, the repeater has to give way.

Key Information: If a radiolocation system experiences interference from a 70-centimeter repeater, the repeater’s control operator must cease operation or make changes to the repeater that mitigate the interference.

Until a change in frequency, power, antenna, or filtering stops the interference, the repeater stays off the air.

Location adds another check in the lower part of the same band. Canada’s amateur band starts at 430 MHz, leaving 420–430 MHz to other services there. To protect them, an agreement between the two countries draws a boundary called Line A.

Key Information:

• Line A is a line roughly parallel to and south of the border between the US and Canada.
• Amateur stations located in the contiguous 48 states and north of Line A may not transmit in the 420–430 MHz segment.

Section 97.3 gives its exact course, which dips well south of the border near the Great Lakes, so check a site against it.

What Receivers Need Protection? #

Some receivers need protection because of what they listen for. An FCC monitoring facility must hear signals well enough to do its work. A nearby amateur transmitter can overload its receiver even when the amateur’s signal is clean.

Radio astronomy listens for far weaker signals: natural radio noise from space. The National Radio Quiet Zone shields that work. It covers parts of Maryland, Virginia, and West Virginia.

Key Information:

• An amateur station must protect an FCC monitoring facility from harmful interference within 1 mile.
• The National Radio Quiet Zone is an area surrounding the National Radio Astronomy Observatory.

Part 97 still uses that name, though the telescopes at Green Bank, West Virginia, now operate as the Green Bank Observatory. The zone doesn’t forbid all radio use, but some stations there must notify the observatory first.

Broadcast listeners get a different kind of protection. Suppose an amateur station interferes with domestic broadcast reception on receivers of good engineering design. Section 97.121 then keeps it off the frequencies causing the trouble from 8 to 10:30 p.m. local time, and on Sunday from 10:30 a.m. to 1 p.m. as well.

Key Information: If an amateur station causes interference to domestic broadcast reception on receivers of good engineering design, the FCC may require it to avoid transmitting during certain hours on the frequencies that cause the interference.

Which Authority Governs the Structure? #

Tower height brings aviation into the picture. A structure more than 200 feet tall needs FAA notice and FCC registration. Aircraft fly low near runways, so close to an airport a shorter structure can matter too. Local zoning is a separate matter. Local governments have legitimate reasons to regulate structures, and amateurs need antennas that work. A 1985 FCC ruling known as PRB-1 sets the balance between them.

Key Information:

• When erecting an amateur station antenna structure at or near a public-use airport, you may have to notify the Federal Aviation Administration and register it with the FCC as required by Part 17 of the FCC rules.
• PRB-1 applies to state and local zoning regulations.
• PRB-1 requires state and local regulations affecting amateur radio antenna size and structures to make reasonable accommodations for amateur radio.

Reasonable accommodation does not mean a tower of any height anywhere. Local rules may still limit an antenna if they are the least regulation needed for a legitimate local purpose. Two other sets of rules sit outside PRB-1 entirely: a homeowners association’s private covenants and the aviation rules above.