Cam - the shorting out theory is of course possible, if the film is conductive at its surface. A simple test with a ohm meter will establish that. Why not get a sample and test it but dont pierce the surface of the film. As stated, I was being very simplistic in my explanation. MY RF theory is a little rusty too, however I was not really trying to imply that it was acting as a shield, although it does read that way in retrospect. The more likely effect (as you have indicated) is reduced efficiency due to the ground plane effect of a large metalic surface laying across the aerial (window) surface. This will greatly affect the properties of the aerial and MAY cause loss of RF sensitivity at the desired frequencies. It may also increase sensitivity at undesired frequencies leading to increased noise to the RF amplifier. I suspect that the RF front end of the radio is not very sophisticated and relys on a band pass filter (500khz - 110Mhz) and a rather simple AGC system. So an increase in RF noise in these frequencies would reduce the RF amp gain and thus reduce the wanted signal being provided to the rest of the circuit. Just for clarity - this is opinion based on a little knowledge and some assumptions I have made (which may be dangerous). Until either I or someone else can provide catagoric facts it should be taken as such