Spectrum Management - From the Early Years to the 1990s

by Laval Desbiens

Page 09 of 26

Locating Electrical Interference


In the first years of the Radio Branch, few people had a driving permit and very few inspectors. At the time, it was also thought to be dangerous for inspectors to drive a vehicle at the same time as they were looking for sources of interference. The Department thus employed drivers specifically to drive the vehicles, while the inspector - with or without a permit - worked the equipment!


In time, locating line interference became the job of these "drivers" and they were eventually reclassified as "electricians". A few of them remained employees of the Department until the late 1960s; they really did not need inspectors or technicians to locate line interference although they did train many of them.


Quebecs' old timers remember Horace Boucher who trained many in the Montreal district to recognize the various noises caused by electric installations and identify the source and/or cause. Alban Violette relates "... a sincere man, who had many children and a meagre salary, ... he would guess the distance of the source of the noise quite well by the intensity of the harmonic and would easily identify the defective part upon reaching the source."


The Quebec City district also had one of these skilled electricians, by the name of Desrochers, on its staff. On the west coast, George Smith was also a gifted technician who worked until 1958. All had been promoted to radio-electrician because it was quickly noted that these people could easily do the work without the help of an inspector.


The methods to locate interference established by engineer Horace O. Merriman in the 1920's are the same ones used today. Except for the mallet, which still looks the same, the equipment has improved and some instruments have been added. (Photos of tools appended)

The steps to locate interference are:

ˇ    Ensure that the interference is coming in on the receiver's antenna. Is the receiver faulty or is it inductive interference?

ˇ    Is it atmospheric static or inductive interference?

ˇ    Is there a fault in the electric circuits or in any of the electric appliances in the household?

ˇ    How large is the area affected by the interference?

ˇ    Test all suspected sources.

When on patrol for interference, inspectors naturally had to get as close as possible to the noisy area and that was done by using all-wave receivers, whip and directional antennas and probes.


For inductive interference, the principle was to begin by identifying the noise at the complaining party's home so as not to set off on a wild goose chase. It was important to look for the cause of the main noise affecting the receiver in the residence first, and it was very easy for a less alert listener to pick up the wrong noise once outside!


Naturally, before going outside, care was taken to ensure that it was not the receiving set that was faulty, and also that the source of the problem was not inside the home. Substituting another receiver or interrupting the power supply could give some good indications.


Second, once the noise was identified with the test receiver outside, inspectors had to listen to the noise and approach its source by tuning the receiver to increasingly higher frequencies. They then had to manipulate the attenuators, gain control and directional antenna (dipole or Yagi) and finally, in the case of noise caused by an electric installation, for instance, conduct a visual inspection, do a mallet test, shake the guy wires of poles and interrupt the power supply, depending on the circumstances, in order to identify the source.


Some inspectors with a well-trained ear could identify the probable cause by the sound: thermostats, motors, isolators, posts or struts, secondary current distribution, 25 kV primary, 130 kV or more, and work accordingly.


In 1945-1950, some lighting lamps were good generators of parasitic oscillation because of the material used for the filament. Paul L., an inspector at the Quebec City district office in the 1950s relates "... I had already picked up such a lamp and I brought it with me for occasional demonstrations. One day, at a hotel in Gaspé, I could not listen to my favourite radio program because other clients were in the lobby listening to a political speech. I remembered my lamp, went up to my room and set it up. I went back downstairs and there was such a noise on the radio that everyone left, grumbling... I went back upstairs, removed my lamp and returned downstairs smoking my pipe. A good program..." (a bad example) Paul was a small, nervous man and very crafty. He had been a radio operator on the Lady Grey, a government ship that sank in Quebec City.


Of all the equipment used to detect line interference, the most useful turned out to be the ultrasound microphone equipped with a reflector that made the device very directional. Without fail, it allowed identification of a defective bolt, washer or insulator at an installation, as long as the spark causing the interference was in the open air(and even in enclosed areas). When I was at Centre St. Rémi centre in Napierville, a representative for a major supplier told me about a microphone that telephone company employees used to detect gas leaks in their pressurized lines. I figured that it could be very useful for interference. After conducting some conclusive tests and making the appropriate recommendations, the Department provided some for all its offices.


No less useful for this type of work was the mallet - but we had to be careful. Some inspectors had the fright of their life when they saw insulators or mechanical parts go flying by their head after they had given a pole a good blow with the mallet.

Around 1994, a decision was made to convince the hydroelectric power companies, the industry and the public to take charge of locating interference. Many reasons served as an argument for this change.


For instance, the Department was doing work that was the responsibility of the hydroelectric power companies. There were numerous occasions when we spotted defects that, had they not been reported by staff working on interference, could have caused major outages.


It was also not the Department's actual responsibility to check the appliances or installations of people who complained of interference to determine whether they were faulty. Year after year, statistics showed a large proportion of cases where receiving sets were the source of the problem. The Department was providing a free service.


The changing climate in government caused the Department to reexamine its role, and as a result, it no longer offers services deemed non-essential or that could be delivered more effectively by the private sector. Investigating and locating sources of interference are two such services.


Spectrum Management - From the Early Years to the 1990s

by Laval Desbiens