2004

Interference to Air Traffic Control
By: Shaun Morgan

Shaun Morgan

Shaun Morgan is a Spectrum Management Officer with the Spectrum Management Program. He works in the Vancouver Island District Office in Victoria, BC. 

As a Spectrum Management Officer, my primary duties focus on the orderly management of the radio frequency spectrum, which includes all manner of radio waves, from about 3 kHz to 300 Ghz. Spectrum management accomplishes this by issuing authorities (such as radio station licenses) and maintaining and ensuring its continued health through the enforcement of the Radiocommunication Act, and associated regulations, policies and standards. Part of my job involves the issuance of these authorities and the resolution of interference problems that can jeopardize the use of these authorities. Spectrum Management Officers work to make sure that the radio frequency spectrum is operating smoothly.

The following case story illustrates one small but vital facet of the work a Spectrum Management Officer may be called upon to perform, the suppression of Harmful Radiocommunication Interference:

It’s January 2, 2004 – I receive a call from the Air Traffic “Area Control Centre” (ACC) at Vancouver International Airport. They advise me that pilots along high altitude flight paths within the Vancouver ACC zone are reporting hearing superfluous chatter on the prescribed radio channel. At times, the aircraft are unable to hear Air Traffic Control directions over the interference. This represents a safety hazard, as communications between Air Traffic Control and aircraft are being compromised. The Air Traffic Control stations on the ground can’t hear the interference. The signal is too weak. They’ve called us to enlist our help in resolving this aeronautical interference problem. 

Initial information provided by Air Traffic Control states that aircraft flying at elevations of 30 000 feet have reported hearing interference on the ACC radio channel while flying over Vancouver Island, from south of Victoria to north of Campbell River – a distance of approximately 300 kilometers! I request that Air Traffic Control try and get as many details as they can from the pilots experiencing the interference, such as names of people, places, radio call signs, etc., and the times they were heard. This type of information can be vital to resolving a problem of this nature. They say they will try. Given the large area, and few details, there is not much information to go on.

February 2, 2004 – Air Traffic Control has tried to gather as much information as they can with respect to times, names, or places that pilots may have picked up. The information they’ve gathered, however, is limited. We’ve just caught part of a radio station call sign: VE7. That is the prefix assigned to Amateur Radio stations operating in BC. 

Now we have a lead. 

Little by little we pick up tidbits of conversations heard by the high-flying aircraft: “Jack and his wife Linda ...” “Wayne and Jerri have paid off their mortgage...” and other such statements. There is nothing definitive, but the information provided by Air Traffic Control may help us identify the source. 

I’m now using a remote monitoring station that our office has set up in Nanaimo, BC, to record voice traffic heard on the ACC channel in question. I am hoping our Remote Automated Monitoring System (RAMS) might be able to capture some of the interference heard by the pilots. 

It’s February 18th – I get the break I was looking for. RAMS has recorded a brief conversation between two amateur radio operators. They used their call signs and referenced a location in Nanaimo! Unfortunately, I am still unable to pinpoint the source, as the call signs I recorded are not very clear. The amateur radio operators I contact claim they were not on the air at the time I recorded the interference. The call signs recorded is too garbled to be clearly heard. I’m going to need some help on this problem.

I contact one of our local radio suppliers who is actively involved with the Amateur radio community and ask if he can make some discrete inquiries within the amateur community. He agrees, and I provide him with the bits and pieces of conversation we’ve gathered. 

It’s now almost the end of the day and I receive another offer of assistance from the BC Amateur Radio Coordination Council ( BCARCC ), who coordinate repeater operations among amateur groups.

I guess word travels fast within the amateur community, because I hear back from BCARCC, and they claim that the interference is likely coming from a station operated by the Nanaimo amateur radio club. Someone there knows someone who has paid off their mortgage. 

I speak to some of their members, and with the information I’ve recorded with RAMS, we confirm the identity of the radio station operators, and the amateur radio repeater station they’re using.

The club agrees to turn off their repeater until we can determine what is causing the radio station to radiate a spurious signal falling onto the Aeronautical Communications band. They are being very cooperative and immediately shut down the offending station. They are also working with us to identify the mechanism responsible for causing the problem. 

Monday, February 23rd – I receive an email from the a club member that says they have identified a faulty Duplexer, and that it will be replaced. (A duplexer is a passive device that allows a transmitter and a receiver to share the same antenna.) The Nanaimo club has agreed to keep the station off the air until I can attend, to ensure the problem has, indeed, been dealt with.

Tuesday, Feb. 24th – I am overseeing the replacement of the problem device, and test the output of the repeater to ensure that the interference problem has been successfully resolved.

Once I am satisfied that everything is operating as it should, I advise Air Traffic Control and our Management team in Victoria that the interference has been resolved. 

This case, albeit a bit out of the ordinary, offers a snapshot of one of the many duties that the Spectrum Management Officers of Industry Canada perform each and every day across Canada. With the use of technology, skill, determination, diligence and, most importantly, cooperation, the Spectrum Management Program works to ensure that Canadians enjoy the many services and benefits that are provided through the use of our airwaves.