A method for a wireless local area network performed by an access point (AP) configured to communicate over a primary subchannel and a secondary subchannel. The AP transmits a frame including a quiet channel element to a receiving station. The quiet channel element indicates that the secondary subchannel is to be quieted during a quiet interval in which the AP tests the secondary subchannel for a presence of radar transmissions and the receiving station does not send any frame to the AP. The quiet channel element includes an AP quiet mode field indicating whether a communication to the AP is allowed within the primary subchannel during the quiet interval. The primary subchannel and the secondary subchannel are quieted during the quiet interval if the AP quiet mode field indicates the communication to the AP is not allowed with the primary subchannel during the quiet interval.