Band intruders
| Band intruders | |
|---|---|
| What they are | Non-amateur transmissions inside amateur bands |
| Common examples | Over-the-horizon radar, military data signals, broadcast and voice traffic, fishing radios and buoys |
| Where it matters most | Bands allocated to amateurs exclusively, such as 20, 17, 15, 12 and 10 meters |
| Worldwide body | IARU Intruder Watch Service (formerly the IARU Monitoring System) |
| Monitoring | |
| Set up under | IARU Administrative Council Resolution 24-1 (2024) |
| Earlier US name | ARRL Intruder Watch |
| Newsletter | Monthly, published by IARU Region 1 |
| Region 2 reports | monitoring@iaru-r2.org |
| Not covered | |
| Amateur rule violations | Handled by the Volunteer Monitor program and the FCC |
Band intruders are non-amateur transmissions found inside the amateur bands, where they have no right to be. They range from powerful military radars that wipe out a whole slice of a band to fishing fleets chatting on 10 meters. Most come from outside the United States, so an intruder can't simply be reported to the FCC and shut down.[1] Instead, volunteers around the world identify and document these signals, and the International Amateur Radio Union (IARU) and its member societies ask the governments concerned to act.
Exclusive and shared bands
Whether a signal is an intruder depends on the band. Some amateur allocations are held by amateurs exclusively in most of the world; the 20, 17, 15, 12 and 10-meter bands are examples, as is 7.000 to 7.200 MHz on 40 meters.[1] Any non-amateur signal there is an intruder. Other bands are shared. On the 30-meter band, for example, amateurs are secondary users, so a licensed fixed station there is a legitimate user, not an intruder, and amateurs must avoid interfering with it.[1] Monitoring work concentrates on the exclusive allocations, where amateurs have the strongest case.
Common intruders
The monthly reports of the IARU monitors show the same kinds of signals again and again:
- Over-the-horizon radar. These high-power HF radars, used to watch aircraft and ships far beyond the horizon, sound like a loud buzz, rattle or sweeping tone and can occupy many kilohertz. Recent reports list Russian radars of the "Contayner" type and Chinese radars nicknamed "Foghorn" on 40, 30, 20, 17 and 15 meters.[2]
- Military and government data. Frequency-shift keying (FSK), naval Morse code and data links such as STANAG 4481 and Link-11 turn up regularly, especially on 40 and 20 meters.[2]
- Voice and broadcast traffic. SSB transmissions connected with the war in Ukraine, and occasional stations playing music, are reported on 40 and 20 meters, and AM voice stations turn up on 17 meters.[2]
- Fishing radios and buoys. Fishing fleets use SSB on 30 and 20 meters, and GPS buoys of the kind used to mark fishing gear have been heard beaconing on 10 meters.[2]
- Illegal users. On 10 meters, monitors regularly log Brazilian truckers and other unlicensed "outbanders" using AM.[2]
A software-defined radio or a panadapter makes intruders much easier to spot and identify, because the shape and width of a signal on the waterfall often gives away what it is.
The monitoring system
In the US this work was long known as the ARRL Intruder Watch. It later became part of the IARU Monitoring System (IARUMS), a worldwide network of volunteer monitors organized by region under regional coordinators.[1] In 2024 the IARU Administrative Council adopted Resolution 24-1, which replaced the monitoring system's terms of reference with those of the IARU Intruder Watch Service (IWS).[3] Under it, member societies are encouraged to appoint a national coordinator who leads volunteer monitors, and a steering committee coordinates the work.[3] Region 1's monthly newsletter has used the new name since April 2025.[4]
In the Americas (IARU Region 2), the monitoring page still uses the older name and asks monitors to send observations to the regional coordinator.[5] A useful report gives the frequency, the date and time in UTC, the mode, the signal strength, any identification heard and remarks, and an audio recording, preferably as a .wav file, if possible.[5]
What happens to reports
Monitors have no authority over the signals they find; their job is to identify and document them.[1] When a case is well documented, it goes to the member society in the country concerned, which can raise it with its own government.[3] Governments, not amateurs, deal with one another over harmful interference, and the IARU contacts the International Telecommunication Union only through its International Secretariat.[1][3] Results come slowly but do come: the Region 1 monitors reported success against SuperDARN research radar transmissions on 20 meters in 2023 and saw a clandestine station go silent in 2022.[4]
Interference from inside the United States is different. The FCC has no power to order a foreign station off the air,[1] but it does enforce the rules against domestic violators. Problems caused by amateurs, such as deliberate interference or operation outside license privileges, are outside the intruder service's scope;[3] in the US they go to the ARRL's Volunteer Monitor program or the FCC.
See also
- International Amateur Radio Union
- Volunteer Monitor program
- Radio frequency interference
- WebSDR
- Shortwave listening
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 ARRL / IARU Monitoring Program, ARRL.
- ↑ 2.0 2.1 2.2 2.3 2.4 IARU IWS Newsletter, IARU Region 1, September 2026.
- ↑ 3.0 3.1 3.2 3.3 3.4 Resolution 24-1: Revised terms of reference for the IARU Monitoring System, IARU Administrative Council, 2024.
- ↑ 4.0 4.1 Intruder Watch Service (IARU IWS), IARU Region 1.
- ↑ 5.0 5.1 IARU Monitoring System R2, IARU Region 2.