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The History of

ELECTROMAGNETIC COMPATIBILITY ADVISORY BULLETINS

W. J. ( Bill) Wilson

 

By the mid-1970s the number of radio stations operating in support of commercial activities was probably close to half a million. Most of these stations were operating in the built-up areas of the country on frequencies above 30 MHz. While we had placed a ceiling of 125 watts effective rated power on the most popular class of station, land mobile base stations, many stations still continued to suffer harmful interference that resulted from this spectrum congestion. Most were operating properly on different frequencies and even in different bands. Additionally, off-air television reception was increasingly affected by transmitters which, of course, were operating outside the TV bands. Only subscribers to CATV were spared this trouble.

 

We had about reached the point where that kind of interference could no longer be corrected by the way transmitters were designed and installed. It had come to the point where manufacturers had to design and build receivers with sufficient immunity to transmitted signals outside the receivers' desired pass-band. Just how to help them understand what needed to be done was the problem that concerned me.

 

One day I developed a dandy head cold and rather than give it to the staff of Radio Regulations I decided to stay at home for a few days. Because we were having problems of a different kind with the General Radio Service, I thought it would be a good time to listen to the GRS band in the Ottawa area and find out, if I could, what was happening. My receiver at home was a general coverage set with flywheel tuning and a slide rule dial. I turned it on and spun the tuning knob to move the pointer across the dial from about 10 MHz to the 27 MHz band. As the pointer passed over certain spots on the dial there was a great burst of signals, and in between those bursts relatively quiet spots. I got out a copy of our frequency allocation table and found out that the loudest bursts occurred when the pointer hit an HF broadcast band. The bursts were not quite so loud on the Fixed, Maritime Mobile, Amateur and GRS bands. On the Ottawa NRC Time Signal frequencies the signals were, of course, much louder but very, very narrow in width.

                                                                  

 It suddenly dawned on me that my receiver was giving me a picture of the "radio environment" below 30 MHz around my home in Ottawa. I felt "environment" was the right word as I was concerned with external radio conditions in the immediate surroundings in which people live and work. Had my receiver been tunable above 30 MHz I would have had a picture of the radio environment above that frequency.  Thus if one wanted to communicate by radio in my area, for example, the receiver would have to be designed to operate in that radio environment just as my body would have to be able to breathe in Ottawa's atmospheric environment if I wanted to live in Ottawa.

 

Some years prior to this we had had in the Department two kinds of high frequency radio spectrum scanners but they had been acquired to find clear high frequencies to be used for H.F. radio communications circuits across and to northern Canada. We had never thought of them as showing us the radio environment because we had had so few H.F. stations that the interference problems of the kind that we were now experiencing had never occurred.

 

Clearly, radio receiver manufacturers had not taken into account the "radio environment" of large municipalities where the receivers they made were expected to operate satisfactorily. Surely we, as managers of the radio spectrum for the Department of Communications in Canada, who knew well about radio frequencies, radiated powers, antenna heights and locations, now had a responsibility to describe that environment if Canadian engineers were to be able to research, design and build radio equipment that would serve licensees properly in the radio systems that we authorized and they installed.

 

A few days later I returned to work and went immediately to see Garth Roberts, our engineering expert on electromagnetic compatibility matters to get him to prepare a public information document describing the crowded radio environment in the built-up areas of Canada. I suggested to him that he prepare a graph showing the radio frequency spectrum from 100 KHz to 10 GHz along the X axis. The signal strengths in microvolts per meter that might be expected in each frequency band used in any Canadian built-up area could be represented by vertical bars parallel to the Y axis. The bar heights could be related to the signal strengths they represented. There was some discussion as to how field strengths might be determined but I suggested that could be calculated based on information found in our frequency lists and licensing records. The interference problems we faced would have to be explained and the graph and solution be supported by the information document.

 

Garth gave my idea a cool reception. He said, "Bill this just won't fly." However, I persuaded him to see what he could do anyway. He took on the job with the assistance of  Nihat Yazar, an engineer on his staff.  Nihat, who had considerable experience in resolving the compatibility problems involving many radio transmitters and receivers operating simultaneously in close proximity, understood the problem well. In a few months I was very pleased when Nihat sent me the very first copy of "Electromagnetic Compatibility Advisory Bulletin 1" entitled "Immunity of Electrical/Electronic Equipment Intended to Operate in the Canadian Radio Environment (0.014 – 10,000 MHz). A handwritten note on it to me said, "W.J.W. Your baby graduated 6/9/77." and was signed, "N. Yazar".

 

             Many months later after I had retired I met Garth at a Radio Advisory Board of Canada meeting and he greeted me with, "Bill! Was I ever wrong about EMCAB 1. I never really expected it would do so well. And we've had all kinds of requests for copies of it from across Canada and from countries around the world."   I confess that I've felt a little warm about EMCABs ever then and that I've kept the copy which Nihat sent me.

 

Since 1977 the Department has updated the first bulletin to take into account developments in technology and spectrum usage and issued additionally EMCAB 2 on criteria for resolving immunity complaints and EMCAB 3 on implementation and interpretation of the interference-causing equipment standard for digital equipment.  

 

W. J. ( Bill) Wilson

Ottawa, November 5, 2003.  

 

 

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