RFI Mitigation

The Green Bank Observatory is a unique resource for Radio Astronomy.  We are located in the National Radio Quiet Zone (NRQZ) which provides protection from permanent, fixed, licensed transmitter services. Our location, surrounded by National Forest and the mountainous terrain of West Virginia, also serves to protect observations. Additionally, the West Virginia Radio Astronomy Zoning Act allows us to prohibit the use of any electrical equipment within a ten mile radius that causes interference to Radio Astronomical Observations.

On the Green Bank Site itself, our protection policy differentiates two zones, one for the laboratory, housing, and visitor facilities (Zone 2), and one for the Radio Astronomical Instruments themselves (Zone 1 aka the Radio Astronomy Instrument Zone) as illustrated on the following map:

Zone Map

In Zone 1, the “ground zero” of our instruments, the general philosophy for interference mitigation is a preventative, proactive approach; interference potential is assessed through testing, and equipment is shielded, filtered, etc. as necessary before installation. We require that all installed equipment be RFI tested and mitigated to comply with the limits stated in ITU-R RA.769, assessed with respect to the prime focus point of the GBT at its highest elevation. We additionally attempt to protect this most sensitive zone by limiting motorized traffic to diesel vehicles to avoid strong broadband emissions from spark plugs. We also instruct all visitors to leave their smartphones and digital devices behind when they go on the site tour, whether by bus tour or foot traffic. So, for Zone 1:

  • All digital cameras, cell phones, fitness trackers or similar devices should be left at the Science Center (lockers are provided for this purpose), Jansky Lab, or in your car or residence. All tour buses are also fitted with a Faraday cage for storing items temporarily.
  • If your work or research involves installing equipment in Zone 1, bear in mind that it must be tested in the anechoic chamber and mitigated to the required levels before you install it.
  • For portable equipment, bring only what is absolutely necessary for your work into Zone 1, and don’t leave it there – that counts as “installed”.
  • Only diesel vehicles are allowed in Zone 1.
  • Remember that the GBT isn’t the only instrument on site; we have many projects sharing our facility. Hence, coordinating with the GBT observation schedule does not protect other research; please be considerate.

In Zone 2, the laboratory, housing, and visitor facilities, we differentiate between intentional radiators and unintentional radiators. An intentional radiator is any electronic device that intentionally transmits radio waves. All intentional radiators except for a select list of coordinated devices which are absolutely necessary for safety (the 43 MHz site radios, for instance) are strictly prohibited in Zone 2. Prohibited devices include cordless telephones, and wireless networking devices. A good rule of thumb is, if it uses RF energy to communicate, it almost certainly exceeds the ITU-R RA.769 limit, and we ask that you please don’t use it here. With regard to unintentional radiators, such as your laptop without its wireless card, we request that you use them as needed, and power them off when not in use. Certain unintentional radiators in Zone 2, particularly those that have particularly strong emissions, such as microwave ovens, and those that need to be powered on 24/7, such as the network servers, are confined to shielded rooms or shielded enclosures.  Employees who live in observatory housing are bound to these regulations by a clause in the housing lease. As a visitor, all you need to remember for Zone 2 is:

  • Intentional radiators are prohibited, please leave them at home or powered off and in your car.
  • Use electronic equipment as necessary, but please power it off when you’re not using it.

Following these simple guidelines goes a long way towards preserving the relatively RFI-quiet environment here. Your cooperation is vital to protecting the research that goes on here. If you have any questions or concerns regarding our on-site RFI policies, please contact the interference protection group (gbipg <at> nrao <dot> edu).

While there is currently no RFI monitoring antenna on site, the GBT is used periodically to monitor the sky at different frequencies to look for interference. The monitoring scans are available both online and through a site-based gui. The gui allows for significantly more data to be displayed and uploaded, while the web-based system provides a quick and easy look into the GBT’s RFI environment for everyone.