Use an external modulator which switches the radio's antenna input from the car radio antenna to the Sirius signal as you turn the Sirius unit on and off. My radio remains tuned to my favorite local station which has a strong and full quieting signal throughout my travels, but when I turn my XM unit on, the XM unit completely overpowers the local station. This method has the added advantage of not transmitting any noticeable signal to other drivers on the road, making you a more responsible neighbor. With a half dozen installs over the past decade, this is the only way I ever have installed and ever would install.