We consider single-hop radio networks with multiple channels as a model of wireless networks. There are n stations connected to b radio channels that do not provide collision detection. A station uses all the channels concurrently and independently. Some k stations may become active spontaneously at arbitrary times. The goal is to wake up the network, which occurs when all the stations hear a successful transmission on some channel. Duration of a waking-up execution is measured starting from the first spontaneous activation. We present a deterministic algorithm that wakes up a network in O(klog1/bklogn) time, where k is unknown. We give a deterministic scalable algorithm for the special case when b>dloglogn, for some constant d>1, which wakes up a network in time, with k unknown. This algorithm misses time optimality by at most a factor of O(logn(logb+loglogn)), because any deterministic algorithm requires time. We give a randomized algorithm that wakes up a network within rounds with a probability that is at least b34b63bab1da7adb1" title="Click to view the MathML source">1−ϵ, for any 0<ϵ<1, where k is known. We also consider a model of jamming, in which each channel in any round may be jammed to prevent a successful transmission, which happens with some known parameter probability p, independently across all channels and rounds. For this model, we give two deterministic algorithms for unknown k : one wakes up a network in time 47b">, and the other in time when the inequality b>log(128blogn) holds, both with probabilities that are at least 1−1/poly(n).