National Radio Quiet Zone

Most hams never give a thought to where their signal lands once it leaves the antenna. In one corner of Appalachia, people have to. The radio telescopes at Green Bank listen for signals from space so faint that an ordinary transmitter nearby could swamp them.

To protect those receivers, the federal government drew a box on the map more than sixty years ago. If you live in it, visit it, or plan to put a repeater or beacon there, here is what you should know.

What It Is and Where It Is

Part 97 defines the National Radio Quiet Zone as the area in Maryland, Virginia and West Virginia bounded by 39°15′ N on the north, 78°30′ W on the east, 37°30′ N on the south and 80°30′ W on the west. FCC rule 1.924 gives the same box with slightly more precise coordinates. The National Radio Astronomy Observatory (NRAO) describes it as about 13,000 square miles near the Virginia and West Virginia border.

The zone is not a ban on radio, and hams live and operate inside it. What it does is require coordination before certain licensed transmitters go up, so that the observatory can check whether they would cause trouble.

Why It Exists

The FCC established the zone in 1958, in Docket No. 11745, and the Interdepartment Radio Advisory Committee, which coordinates federal spectrum use, set it up the same year. Its purpose is to limit harmful interference to the observatory at Green Bank and to the Navy’s radio receiving facilities at Sugar Grove, West Virginia.

The largest instrument at Green Bank today is the Robert C. Byrd Green Bank Telescope, with a 100 meter effective aperture and coverage from 0.1 to 116 GHz. Radio astronomers measure signals far weaker than anything a ham deals with, so they need the airwaves around their telescopes kept as quiet as possible.

The FCC Rules

The general rule is 47 CFR 1.924(a). It says that applicants and licensees planning to build and operate a new or modified station at a permanent fixed location inside the zone must notify the director of the NRAO in writing. The notice must give:

• The geographical coordinates of the antenna.
• The antenna height and directivity, if any.
• The channel.
• The emission type and power.

The notice can go before or at the same time as the FCC application. The FCC then allows 20 days for comments or objections. If the NRAO objects, for itself or on behalf of the Sugar Grove site, the FCC will consider the record and take whatever action it deems appropriate.

The NRAO’s zone office handles this coordination. It works out the expected signal level at the Green Bank Telescope and, if the numbers pass, issues a coordination letter. Its older coordination pages list Amateur Radio among the services covered, and the office welcomes voluntary coordination even where it is not required. You can read the current procedure on the NRAO National Radio Quiet Zone page.

What It Means for Hams

Beyond defining the zone in 97.3, Part 97 has one operating rule about it. Rule 97.203(e) says that before you set up an automatically controlled beacon in the National Radio Quiet Zone, or change its frequency, power, antenna height or antenna directivity, you must give written notice to the Interference Office of the NRAO in Green Bank. The notice must list:

• The antenna coordinates, ground elevation above mean sea level and antenna height above ground.
• The antenna directivity.
• The proposed frequency and type of emission.
• The transmitter power.

If the NRAO objects within 20 days, for itself or for the Naval Research Laboratory at Sugar Grove, the FCC will consider the problem and act as it sees fit.

Repeaters have no separate quiet zone paragraph in Part 97 today. A repeater sits at a fixed site, though, so the general coordination rule and the NRAO’s process are where to start. The same is true if you are planning a permanent home station with high power or a large antenna. The rule text speaks of permanent fixed stations, so if you are unsure whether your plans count, ask the zone office before you build.

West Virginia State Law

West Virginia has its own Radio Astronomy Zoning Act, found in Chapter 37A of the state code. Within two miles of a radio astronomy facility’s receiving equipment, it is unlawful to operate any electrical equipment that interferes with the facility’s reception of signals from space.

Out to ten miles, the law sets limits on the field strength any electrical equipment may produce, with tighter limits closer in. Equipment that is built or shielded so it does not cause interference is allowed. This law reaches beyond licensed transmitters to all kinds of electrical gear.

Daily Life in the Zone

The strictest rules are on the observatory grounds. Green Bank asks visitors to switch off the wireless signals on their phones in settings before powering them down, and to turn off or leave behind other wireless devices. Digital cameras are limited to the Science Center and the observation deck, while film cameras can be used throughout the public areas.

Closer to the telescopes, only approved diesel vehicles are allowed, because the site policy counts gasoline vehicles as unintentional transmitters. The site policy also prohibits intentional transmitters unless their transmissions are turned completely off, and microwave ovens need a waiver.

Those are the observatory’s own rules for its grounds. Across the wider zone, the federal rules deal with licensed transmitters at fixed locations, and the state law covers electrical interference within ten miles of the telescopes.

Visiting or Moving There

A few simple steps keep you on good terms with your neighbors at Green Bank:

• On a Visit: Leave your handheld and mobile radio switched off on observatory grounds, and follow the staff’s instructions about phones and cameras.
• Passing Through: Keep in mind where the telescopes are, and save long transmitting sessions for when you are well away from them.
• Moving In: Before putting up a permanent station, especially a big one, contact the NRQZ office and ask whether coordination applies.
• Repeaters and Beacons: Coordinate with the NRAO before you build, and for an automatic beacon send the written notice that 97.203(e) requires.

For the wider rules, see our guide to Part 97 in plain English, and for what the telescopes do with all that quiet, read radio astronomy for hams.