Here is the answer to the RCA connector on the bottom of the
docking station.
Thank you for contacting us. The RCA port on the back of the SonicHub docking station is used to handle video output from different devices. Currently only the Simrad brand of products can support video into the unit. This connection will not apply to the HDS units by Lowrance. The SonicHub is compatible with both Lowrance and Simrad units by Navico. Please feel free to contact us if we may be of further assistance. Regards,Navico Customer Service.