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Compiled by the ARRL Laboratory Staff
March 8, 2002
Who's on First? Spectrum Sharing and Unlicensed Devices
Let's talk about unlicensed radio transmitters and the rules that govern them. One thing that can be said about amateurs is that they are protective of their allotted amateur spectrum. The Lab receives inquiries almost weekly regarding unlicensed devices that operate in ham bands. A typical inquiry might be, "I just saw an ad from the XYZ Company about a remote-reading wireless thermometer that operates on 433 MHz. Should someone contact the FCC about removing this product from the market?"
The issue is not quite as simple as that. Unfortunately, most of the devices reported to ARRL are not illegal. They have been properly authorized by the FCC to operate at the power levels and frequencies described in Part 15 of the FCC rules. Intentional radiators must be certificated--as described in this Part--before they can be legally marketed in the US. All approved devices have a label that shows the FCC ID number associated with that device. But how can unlicensed transmitters operate in "our" ham bands?
Share, But Not Alike
Government use of spectrum is not regulated by the Federal Communications Commission; the National Telecommunications and Information Administration--in the Department of Commerce--regulates US Government stations and their operation.
One thing that many hams don't know is that other services and users can use the entire amateur spectrum as described in the FCC rules. In allocating spectrum the FCC sets up a pecking order in which some users have a status higher than other users. In many cases there may be several layers. Users that have protection from other users are called primary users. Users that must unconditionally not interfere with primary users are called secondary users. They are given the clear responsibility not to cause harmful interference to primary operation within that spectrum.
The 70-cm ham band is an excellent example because a number of radio services use it. On 70 cm in the US, the Government radiolocation service (radar) is at the top of the list. In recent months ARRL has received reports of strange signals in the 70-cm band. Various AWAC and other military radars that may be using these frequencies are deployed in US airspace in conjunction with the war against terrorism. Not only are these systems allowed on our band, they are primary and the Amateur Radio Service is secondary. If we hear such government use of the band, it is incumbent on us not to cause harmful interference.
 Experts on all types of interference problems contributed chapters to The ARRL RFI Book |
Many amateur bands, such as 900 MHz or 2.4 GHz, also use frequencies allocated to Industrial, Scientific and Medical devices. ISM includes such uses as RF heat-sealers or RF-driven lighting. They may or may not be designed to radiate, but ISM devices are not permitted to communicate information. However, within the ISM bands, no other operation using that spectrum--such as Amateur Radio--is offered protection from ISM operation. More information about the ISM bands is found in The ARRL RFI Book.
At the bottom of the list are the unlicensed devices regulated by Part 15 of the FCC rules. Part 15 outlines a number of different unlicensed devices: incidental radiators (such as power lines); unintentional radiators (such as computers) and intentional radiators (such as baby monitors and the remote-reading thermometer previously mentioned). The words frequency sharing do not apply to these devices--they operate entirely at sufferance to other users, not protected against interference under any circumstances and not permitted to cause harmful interference.
What are the Limits?
Part 15 sets two limits for RF emissions from unlicensed devices: an absolute limit on the field strength or power from a device, and a secondary requirement that unlicensed devices not cause harmful interference to other radio services. The manufacturer must meet the emissions or power limit, and the operator of the device is responsible for correcting any harmful interference that results from the use of the device.
Are the emissions limits enough to protect sensitive Amateur Radio reception? Unfortunately, no. As an example: on 2.4 GHz, devices are permitted to use up to 1 W of power with an antenna of 6 dBi gain. This signal can be heard for miles. The general limits for intentional radiators on HF--Sec. 15.209 of the rules--permit emissions of up to 50 mV/m at a distance of 30 m from the radiating source. To put this into perspective, this could result in a signal of S9+20 dB into an 80-meter dipole located 100 feet from such a legal source. W1RFI has worked 30 states on HF with a transmitter power of 10 milliwatts. The signal on the other end was figuratively buried in the noise. The only way that maximum emissions limits could protect this type of operation would be to set the limits tens of dB lower than they are now.
The FCC believes that it has set Part 15 device limits that will minimize the likelihood of harmful interference in most cases. Considering the pervasiveness of these devices and the length of time over which these devices have been operating subject to this requirement, these limitations are not likely to be changed any time soon. Any change that might be made would probably not require levels low enough to unconditionally protect all sensitive amateur operation. With the ever-increasing spectrum pressures from prospective users such as SAVI Technology, Inc--which is looking to expand Part 15 use of 70 cm--it will be hard enough for Amateur Radio to convince the FCC to keep the limits set as they now are.
Harmful Interference
However, the rules also stipulate that unlicensed devices are not permitted to cause harmful interference to radio services. The key words are harmful interference. The FCC rules define harmful interference as the serious degradation or repeated disruption of communication. Merely hearing an unlicensed emission in our bands is not harmful interference. After all, how would hams feel if the primary users of 70 cm or 30 meters said that they could hear hams in their bands, so we have to get out?
In one sense the protection against harmful interference is absolute and unconditional. In a practical sense though, there is a limit to how much protection the rules can offer. If a ham hears a strong signal in the ham bands and that signal disrupts the ham's ability to communicate, the operator of the device causing the signal is responsible for correcting the interference. In a crowded residential neighborhood that operator could be any of one's neighbors. In some cases it may be virtually impossible to locate the source. Even if a ham can find the operator, it will be difficult to convince the neighbor that the device he or she just bought at a local electronics outlet is being operated in violation of federal law. It will be a difficult conversation indeed. And what about the ham who lives on a prime location, overlooking a crowded urban area? He or she might be hearing the aggregate of hundreds of unlicensed devices. How can the rules protect against harmful interference in that case?
 FCC regulations require that most devices governed by Part 15 have this informational label affixed to the unit or replicated in the owners' manual. |
What Can Be Done?
ARRL is working on addressing the issues surrounding unlicensed operation. First and foremost, the League maintains contact with the industry. In addition to serving on the Institute of Electrical and Electronics Engineers (IEEE) Electromagnetic Compatibility (EMC) committee, the League has been in communication with manufacturers, the FCC and others who might be able to help. Whenever an FCC rule-making procedure regarding unlicensed operation is put on the table, the ARRL Washington team and ARRL Lab submit comments to the Commission, representing the interests of Amateur Radio. Over the years, the League has won some and lost some--just like every other user of spectrum.
The real issue is the question of actual, harmful interference. Manufacturers, and even the FCC, all acknowledge that under the present rules Amateur Radio is unconditionally protected from harmful interference. How much more protection can one expect than absolute protection? The maximum limits set by the present rules are so high that the only part that protects us is the requirement not to cause harmful interference. Manufacturers, the FCC and unlicensed operators simply must take this rule seriously. If everyone involved in an actual problem does not address his responsibilities fairly, the rules as written do not work.
Has the FCC gone to bat for Amateur Radio? In cases of power-line noise the Commission has been generally supportive, working with ARRL to help resolve cases voluntarily and writing letters to power utility companies in cases where voluntary cooperation is not enough. In a case involving interference from a wireless-internet-service provider--Darwin Networks--the Commission wrote to Darwin, asking how the company intended to resolve the reported interference. If the Commission continues to address actual cases of harmful interference the number of serious problems will remain relatively low.
Getting Help
The ARRL RFI Desk is looking for reports of harmful interference to Amateur Radio from unlicensed devices. ARRL HQ staff knows that there are more problems than the handful reported to the League. If you are having a problem with interference from an unlicensed device, ARRL will offer you information about the rules and how to proceed. Our staff will then contact the operator of the unlicensed device, if that is what you decide is the best remedy. If that is not effective, the League may then take the case to the FCC to seek resolution and to affirm the ARRL's expectation that the Commission will help out, if needed. If you experience harmful interference from unlicensed devices (examples are a neighbor's computer system or interference on 2.4 GHz from wireless devices), please send a report to the ARRL RFI Desk. Include a summary of your case, the names and addresses--and other contact information--of involved parties and equipment manufacturers.
More Information
The ARRL Technical Information Service and the ARRL Regulatory Information Branch have prepared Web pages containing more information about Part 15.
News Item: Electric Utility Company Announces Comprehensive RFI Program:
Many of the cases we have been working on have involved the FCC and it will be a pleasure to report to the Commission that there is some positive news on the front lines. The League extends its thanks to Mike Martin, K3RFI, and PEPCO for taking this very positive, proactive step toward resolving RFI problems.
ARRL received the following email announcement from the RFI Investigator at Potomac Electric Company:
To all customers of Potomac Electric Power Company: As the Interference Investigator for Potomac Electric Power Company (PEPCO), I want to ask for your patience in dealing with RFI/TVI problems which may or may not be caused by PEPCO's power lines or associated equipment. PEPCO has always and will continue to show our dedication to our customers by providing them with the best RFI/TVI locating services possible.
The reason for this letter is, as I'm in the process of fabricating the new PEPCO RFI Locating Vehicle, there may be a length of time where resolution to your complaints may be longer than the normal acceptable response time. For this I apologize. However, I am sure that when the job is complete, response and resolution timing will be back to normal if not faster.
This work is being done to help improve efficiency, safety, and customer satisfaction. As always, I'm available for assistance during normal working hours. You're welcome to call with comments, suggestions, and concerns at anytime. Thank you for you patience and understanding.
Mike Martin, K3RFI, Interference Investigator, Potomac Electric Power Company. Tel: 301-967-5230.
News Item: The ARRL EMC Committee:
At the January 2002 meeting of the ARRL Board of Directors, the Board gave the ARRL RFI Task Group a new name. The committee is now known as the ARRL EMC Committee. Neither the committee membership nor the scope of the committee's work has changed, but the new name is a better match for the terminology used by professionals in discussing what most hams still think of as "RFI."
Every ham who has an RFI problem needs a copy of The ARRL RFI Book. Experts in the various aspects of RFI affecting hams wrote the book. It starts with the real basics--how to deal with the interpersonal aspects of RFI. (Knowing all the technical solutions will do no good if your neighbor won't let you in the house to try them!) Chapters cover the topics of Electromagnetic Compatibility theory as it relates to transmitters, televisions, cable television, telephones, audio devices, computer and automotive RFI. Income from sales of The RFI Book helps pay for the ARRL RFI programs.
The RFI Update column is published monthly on ARRLWeb. The column features information on current activities in the RFI arena, interesting RFI cases handled by ARRL and tips for solving RFI problems. An archive of past RFI Update columns is available. If you have information you believe is useful to the ARRL RFI program, or if you need help solving an interference problem, contact the ARRL RFI team, call the ARRL Laboratory staff at 860-594-0214 or write to the ARRL RFI Desk, 225 Main St, Newington, CT 06111.
