The Seven Network has surprised viewers in Sydney, Brisbane and Perth overnight by switching it's 7HD channel to a simulcast of the primary channel.

DeciderTV understands Seven has made the change to allow for broadcasting of it's summer sport schedule in High Definition for all Metro markets.

Seven has broadcast rights for the Sydney to Hobart Yacht race, and a number of tennis tournaments including The Australian Open.

7HD (channel 70) normally broadcasts the primary Seven channel only in Melbourne and Adelaide, while viewers in Sydney, Brisbane and Perth normally receive a HD feed of 7Mate.

At the completion of Summer, 7HD will return to broadcasting 7Mate in Sydney,Brisbane and Perth for the AFL season.

Seven has made an agreement with the AFL that it will broadcast all games in High Definition.

7HD is not currently available in regional Australia. 

Earlier this week Seven confirmed it would provide a free online streaming service for the Australian Open with live coverage of 600+ matches. Fans will also have the option of paying for an upgraded HD steam with reduced commercials for a fee of $9.99