"The main purpose of the CN Tower is a telecommunication tower," said Jamil Mardukhi, a principal at NCK Engineering.
"Now it's both telecommunications and tourism, but it still plays a major role in telecommunications services in downtown Toronto."
Back in 1973, Mardukhi was given the job of supervising construction crews on the tower's site, and nearly 45 years later he's still involved as the tower's lead structural engineer.
Mardukhi explains that TV stations, FM and AM stations, and cell services use the tower for transmission...
My guess is that he is referring to the HD channels piggybacked on to FM stations, that simulcast AM stations.
ref. - http://www.cbc.ca/news/canada/toronto/c ... -1.4249393