On 6/21/2014 9:21 AM, Ron Roscoe wrote:
> Radio stations are detected at low level inputs by the stray inductance and stray capacitance [and of course the diode] at the base-emitter junction or equivalent. This L and C resonate at some frequency often exactly at the frequency of a local broadcasting station. One of the most effective ways of stopping this kind of interference is to insert a low value resistor, say 470 ohms, in series with the input leads and as close as you can get it to the base emitter junction of the input transistor. This louses up the "Q" of the resonant circuit and reduces the sensitivity of the circuit to RF frequencies.
This does work. Adds noise, though.