Hello Laurence, Thank you for sending this information to the list. Your 30 - 40 db noise attenuation agrees very well with my own findings at 400 kHz: 40 dB for a concrete building and 32 dB for a b
Equipped with rubber gloves and rubber boots and dark goggles, , connect "earth" of the power supply to your door frame..??? Maybe measure DC PD first but not such sense of adventure. G3GVB Consideri