Nothing sharpens the edge of the NFL preseason like lining up against an unfamiliar opponent. For the second consecutive summer, the Broncos will have joint practices before playing their third preseason game, working out against the San Francisco 49ers at Dove Valley.

The Broncos and 49ers will pair off Wednesday and Thursday the week of their Saturday, Aug. 29 preseason game at Sports Authority Field at Mile High. The teams’ joint practices will be closed to the public.

Last summer, the Broncos hosted the Houston Texans in spirited workouts. D.J. Swearinger, a safety with the Texans last year, relished in trash talking during 11-on-11 work, building tension leading into the teams’ preseason game. It boiled over when he caused a concussion in Broncos slot receiver Wes Welker with a hard hit.

Peyton Manning followed with a touchdown pass and taunted Swearinger — leading to an $8,268 fine from the NFL, which the QB called “money well spent.”

Footnotes. Broncos fifth-round pick Lorenzo Doss signed a four-year, $2.4 million contract Thursday. A cornerback who will compete for playing time as a rookie backup, Doss received a $197,000 signing bonus. … The Broncos also signed seventh-round pick Josh Furman to a four-year deal worth $2.332 million. The safety received a $52,784 signing bonus.

Troy E. Renck: trenck@denverpost.com or twitter.com/troyrenck