The CN Tower Story

Broadcast Transmitters at the CN Tower Beginnings

It was in the late 1960’s that the Canadian Broadcasting Corporation (CBC) found that TV and FM coverage from their tower on Jarvis Street in Toronto was being blocked in several directions because of taller buildings which had developed. Their tower was less than 500-feet in height while the Toronto-Dominion Centre, the Bank of Montreal and others, had risen to 800-feet or more. Other stations were having similar problems. For instance, CKFM’s signals from the Bank of Commerce were being blocked in the Hamilton area because of the higher Toronto Dominion Centre.

One of the CBC’s initial plans was for a guyed tower on the east side of the Don Valley Parkway just north of Lawrence Avenue. They may have planned to also locate new studios and offices at that site. But this plan for a tower site was bypassed when the two railways, CPR and CNR, jointly began planning for a broadcasting tower on the railway lands to the west of the Union Station on Front Street. Their planning was done in coordination with the CBC which was expected to be the largest single user of a broadcasting tower and which, like the CNR, was a federal agency.

As plans progressed, Howard Hilliard, CBC’s Regional Director of Engineering, held several meetings with other Toronto broadcasters to encourage them to cooperatively plan to use the proposed CN-CP Tower for all of Toronto’s television- and frequency-modulation stations. In an initial concept described by Howard, the structure was to consist of three cylindrical concrete towers on a common base with two levels high up on the towers which linked all three of them together. These strong, large links were to be several stories high to accommodate the transmitter plants. The antennas were to be at the top of the highest of the three masts. Later, this was totally revised, perhaps as a result of wind tunnel tests.

Final Design

The final plan had the lower 1480 feet being a single, tapered, triangular mast of reinforced concrete with three buttress-type wings to strengthen the mast. At the top of concrete a steel structure extended the height to 1815 feet above grade level. The chief designer was Ned Baldwin of the architectural firm Andrews and Baldwin.

Beginning at the 1100-foot level several floors were built which collectively were called "the Upper Accommodation". The lowest of these floors is an open area for microwave antennas which has a cloth radome surrounding the outside to protect these antennas from the weather while still allowing the radio signals to pass through. The whole floor is pressurized to keep the cloth expanded and away from the antennas. The next floor up is an Outdoor viewing area encircling the Tower. Next is an enclosed Lookout Observation floor. Above that is a Restaurant level with a floor which slowly rotates once every hour around the Tower so diners have an ever-changing view. Each of the next higher floors house, respectively, the television transmitters, then the frequency modulation transmitters, then the power transformers with the ventilation fans. The Roof Level is open with a railing at its edge. Fifty feet above the Roof Level a small-area floor houses large water tanks for fire protection.

From the Roof Level the concrete portion of the mast extends up a further 272 feet where the concrete ends and the steel mast is mounted on it. Around the mast the various broadcasting antennas are mounted. The steel also supports arms which extend radially outward beyond the antennas to support fiberglass radome panels which enclose and so protect the broadcast antennas from the weather. When the steel rose to a height of 1,815-feet above ground, it became the tallest self-supporting structure in the world.

By 1973 Howard had convinced most of Toronto’s broadcasters that they should all move onto this "CN/CP Tower" when it was built. But about that time CP had become uneasy with their part in financing and owning half of the Tower, and they backed out. However the Canadian National Railway liked the project and decided to proceed alone. Thus it became known as the "CN Tower".

Developments by Broadcasters

Perhaps because the initial five television (tv) broadcasters each owned their own antenna they were able to proceed with their plans relatively quickly. However the frequency-modulation (fm) broadcasters had to work in a more cooperative style as they would have to use one common antenna for all fm stations. Also the CBC engineers who had done the initial coordination work had so much work to do in planning the tv aspects of the CN Tower that they were unable to spend much time on the fm systems. They were responsible for CBLT on Ch 5, CBLFT on Ch 25, and TV Ontario on Ch 19 with the last two being combined onto one antenna.

After about 6-months of delay the fm broadcasters themselves invited those who were interested to a preliminary meeting to plan an fm broadcasting system for all users on the CN Tower. The meeting held promise and another was set up two weeks later. Then every two weeks the FM people held another meeting until they were well organized. Wes Armstrong of CHUM-FM was a key policy man, A. H. C. Lewis of CHFI-FM, owned by Rogers Broadcasting was a leader in the financial area, while Clive Eastwood of CFRB/CKFM was chairman and secretary of the meetings. Also from CFRB/CKFM, Peter Searle did the detailed accounting during the initial planning. (Peter, in 2003, still handles the accounting for MFML.) The group was very democratic as even CKEY, an amplitude-modulation station in Toronto which did not have an fm license, was invited and became involved. In the end, CKEY’s application for an fm license was turned down by the Canadian Radio Television Commission.


The construction of the tower began in February 1973 with an excavation for the foundations. Because the base of the foundation was below the level of the adjacent Lake Ontario a ring of about 60 wells were drilled around the edge of the site and a pair of diesel-engined pumps were temporarily installed. This kept water out of the working area but to do so at least one pump had to be operating continuously.

The man in charge of the overall construction of the CN Tower was Malachy (Mal) Grant,- an Irish engineer from Belfast who gained everyone’s respect. For instance, one day when the concrete work was nearing completion, steel cables were being used to lift forms to just below the top of concrete where they would be fastened in place and used to contain reinforcing rods and fresh cement to form the Upper Accommodation. However, after the form was lifted twenty feet or so off the ground the clamps holding the form onto the hoisting cables slipped letting the form slide down. Even after many tests no one could figure out why the clamps slipped on the cables. Then Mal had an idea,- he sent samples of the cable out for a hardness test. The results showed that these cables were too good in that they were harder than specified thus the clamps could not "dig into" the cable to hold its grip. Those cables were replaced with ones which had the correct hardness and the form was lifted 1100-feet with no further problem. It was securely anchored to the concrete mast to enable completion of the Upper Accommodation levels.

One interesting feature of the CN Tower is that there are two "counterparts" mounted at the one-third points of the steel portion of the structure. They are large rings weighing ten-tons each. They are flexibly hung from the mast and are driven by any of several hydraulic rams to counteract swaying caused by winds. There is a pendulum sensing device which feeds information on how much the Tower is leaning to a computer which controls the actions of the rams.

The first transmissions from the CN Tower were on May 1st of 1976 with CBC-TV and CFTO-TV. The FM stations came on air later that month.

Coordinating Committee

As the television and frequency modulation broadcasting stations developed plans for their antennas, transmitters and equipment rooms there were some conflicts both in the use of space,- particularly in the mast and in the microwave radome,- and in the use of frequencies. The Tower’s staff were not familiar with the technical aspects of these problems so a Coordinating Committee was set up with representatives from each station plus people from the CN Tower. The original and long-term chair of that committee was Helmut Berger, the chief engineer of CFTO-TV.

After a new frequency for the CN Tower has been licensed by the Department of Transport the Committee distributes the pertinent information relating to the Tower to all members of the Coordinating Committee. This is because the use of one frequency could cause problems for several other stations, perhaps in different ways for each station. Committee Members included operators of the microwave and other communication antennas on the Tower as well as Broadcasters. There were several types of communications companies, telephone companies, paging companies and radio messaging services operating from the CN Tower. Further, each broadcaster would have at least one license for a remote news pickup channel, some for radio only, while others had channels for television news pickup as well. All these uses had to be coordinated so they did not interfere with each other.

If, after information had been distributed, and there were no objections at the next monthly meeting of the Coordinating Committee, the application was approved to allow its installation at the CN Tower to proceed. Where there were objections, sometimes the Committee could clear them by setting out specific conditions for such a new channel. At other times further sub-meetings would be required to develop procedures which were satisfactory to all Tenants and to the Owner, the CN Tower. One such general policy procedure was that for transmissions in the same frequency band, receiving antennas and transmitting antennas were required to be at separate levels of the Tower. Otherwise a transmitting antenna might be too near a receiving antenna, thus overloading the receiver. Thus receiving antennas for news reporting were usually in the Microwave Level while their transmitting antennas were usually located much higher, on the face of the concrete structure above the Upper Accommodation.

Master FM Limited

The planning for the CN Tower provided space for only one antenna through which all fm stations were to operate. Thus there was a need to purchase a (master) antenna, plus a combiner unit for each station to allow it to operate on that antenna. A company called Master FM Limited was set up by the fm broadcasters to purchase these and to rent space from the Tower for the combiners.

I thought that the financial planning for the fm stations was quite ingenious. It created a new company, Master FM Limited (MFML), which was to own and operate the antenna and the combining networks. Each fm station signed a rental agreement with MFML for the lease of their portion of these facilities, with rent to be paid monthly. These lease agreements were taken to a bank and a loan of 1.6 million dollars was requested. The bank looked at the leases and even though the five stations were established, reliable broadcast companies, the bank requested, and received, agreements of "lease and license" whereby if a station defaulted on their payments the bank became the virtual owner of that station. On this basis the bank agreed to provide the loan to MFML.

Each of the five stations had invested $2,000, so the total initial cost to set up the Company was only $10,000 yet through the leases it provided for an initial capital fund of $1,600,000. The monthly rental payments from each station to MFML provided for repayment of the loan and for space rental. Each station also had to pay its own monthly rent to the CN Tower for their transmitter floor space and for their right to radiate from the Tower.

In 2002, MFML installed and began operating a Digital Radio Broadcast System (DBRS), which was "...intended to ultimately replace FM broadcasting.". These were FM stations that had been on air on a commercial basis previously.

Canada adopted DBRS - the "Eureka 147" system which is used in the United Kingdom and most of Europe as well as Taiwan, Singapore. In the US, standards are being developed to enable digital broadcasting on the existing AM & FM channels simultaneously with existing broadcasts with a minimum of interference to the existing broadcasts. 

As at January 1, 2003, broadcasting services on the CN Tower included 7 television stations, 8 FM stations and 12 DRBS stations.

By 2017, the antenna broadcast over 30 Toronto television and FM radio signals across Southern Ontario in addition to wireless paging and cellular telephone signals.

Author - Clive Eastwood, Chairman & Secretary of the original committee, and Vice President, Engineering of CFRB (retired)

January, 2003

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