For large-scale Wireless Sensor Networks(WSNs), cluster-based architecture is desirable. Conventional short range sensor radio, however, is often inefficient for the inter-cluster communication due to the large distance between cluster heads. One solution is to use a longer range radio for inter-cluster head communication. In this paper, we consider a dual-radio cluster head with IEEE 802.15.4 and IEEE 802.11b. A key issue is that 802.15.4 and 802.11b use the same frequency band at 2.4 GHz, so that they can potentially interfere with each other. We analyze this interference behavior via testbed experiments. Our results indicate that with a simple relaying mechanism, interference was quite high even when orthogonal channels are used for two radios. This strongly suggests the need of smarter relaying mechanisms.