low-pass filter

RO r 1,00 i R3 *R0+141 = 22 k RL = 4k7 6.5kHz Most communication receiver de- signers assume that "anything above 3 kHz can be cut out" and sometimes a series of four RC filters in a row are given in the receiver. It is obvious that frequency characteristics drop- ping by 12 dB or more at frequencies between 2.5 and 3 kHz are far from ideal. The real object of the exercise is to remove the broadband noise without affecting the frequency characteristics within the range re- quired. In other words, it is better to remain at 1 dB with as sharp a cutoff as possible after 2.5 or 3 kHz. The configuration described here already fulfils this function with only one section. The circuit contains 80546 AM, medium-fi: C2 = 6n8 C3,C4 = 10 n RL = 10 k C5 = 33 n Notch characteristics: — 6 dB: 6 kHz —54 dB: 9 kHz ripple: 1 dB nothing but a single IC and a few other components. Although it ap- pears to be decoupled through C5, this is in fact not the case, because the input circuit is part of ...