Some Bay Area television stations are switching frequencies, requiring a channel rescan by viewers who use an antenna.

KTVU (Fox 2) made the switch Monday, and the seven-week window for KGO, KNTV and KRON opens on Saturday. Several smaller stations are also scheduled to make the change this spring.

The channel number on the TV does not change, and the rescan will be done automatically for viewers who use cable or satellite service. Those who get free over-the-air broadcasts using an antenna, however, will need to manually initiate the rescan.

For most people, that requires just selecting “scan” or “autotune” from the TV or converter box menu. The process usually takes a few minutes.

In some cases, the antenna may need to be disconnected or the converter box rebooted to complete the scan.

Viewers can check the timetable for stations in their area on the websites of the Federal Communications Commission and the National Association of Broadcasters. Those sites also have more information on how to run the rescan.

The FCC’s consumer hotline phone number is (888) 225-5322, option 6.