I think the "Radio filter" mentioned is NOT the standard ADSL Microfilter you may be thinking about. I worked for BT for 23 years and we often had to fit filters to stop local AM broadcast transmitter interference being picked up by newer electronic phones and microphones. It was never a problem with old dial types and carbon granule microphones. Broadband was not common at that time, and I'm left wondering how one of these would affect ADSL signals....