The HD switching is looking for about 55dBf to switch from analog to HD. Also, the signal must be in the neighboorhood of +50 S/N to allow switching. Some antennas do contribute noise, especially the amplified ones, which is a no-no. My Terk FM -Pro does not work well on HD. An antenna that contributes little noise is a coxial sleeve. In addition, perfect impedance match is also important because it causes self-inflicted multipath. Don Scott
HD radio and old antennas
Does anyone know if old AM/FM antennas (like the ones made by Terk) will still work with HD radio? Some of Terk's products are listed as "digital ready" (not the ones I own) but I don't see any reason why the antenna technology would change.