Review on Enhance Your Audiovox Sirius Experience with the SIREXT50 Indoor/Outdoor Antenna Extension Cable - 50-feet, Black by Eric Power

Like most people who install Sirius radios outdoors, I've found that using the included car antenna actually works better than a directional indoor antenna (and it's flat, too). Note that this cable will not work with car antennas as they are usually L-shaped. This only works if the end of your antenna is straight. I don't know why it wasn't listed in the description. Also on the subject of water resistance. The instructions say to install in a specific direction. It looks like if installed in that direction there would be no water ingress. If installed upside down, it will fill with water. For the rest it works.