29-07-2015, 07:15 PM
(This post was last modified: 29-07-2015, 07:17 PM by Geordie McBoyne.)
Here's the circuit of the Dickert sound interference limiter.
In the Spreadbury book it took four pages to describe on how the circuit works. Here's a concise description. The negative going demodulated audio is developed across the diode load resistors R1 and R2. Both have the same value, say 50Kohms. The detector diode also functions as a clamp ensuring that the output never goes positive. The audio developed across R2 is exactly half that of the total load resistor, R1 & R2. The average value of the signal is developed across C2, 0.5mfd. R3 is typically 1megohm. Under normal conditions diode D2 cannot conduct. When a high amplitude interference spike comes along D2 conducts and the spike is dumped into C2.
Normal TV practise dictates that the sound channel bandwidth is much greater than an AM radio receiver, this ensures that the interference spikes are preserved. It begs the question will this type of interference limiter ever work in a radio receiver?
Geordie McBoyne.
In the Spreadbury book it took four pages to describe on how the circuit works. Here's a concise description. The negative going demodulated audio is developed across the diode load resistors R1 and R2. Both have the same value, say 50Kohms. The detector diode also functions as a clamp ensuring that the output never goes positive. The audio developed across R2 is exactly half that of the total load resistor, R1 & R2. The average value of the signal is developed across C2, 0.5mfd. R3 is typically 1megohm. Under normal conditions diode D2 cannot conduct. When a high amplitude interference spike comes along D2 conducts and the spike is dumped into C2.
Normal TV practise dictates that the sound channel bandwidth is much greater than an AM radio receiver, this ensures that the interference spikes are preserved. It begs the question will this type of interference limiter ever work in a radio receiver?
Geordie McBoyne.
