1. EMI Filter for Audio Equipment By K5PA March 5, 2014

2. Problem Statement During amateur radio transmission, our audio equipment would pick up the transmission, especially during CW operations Design and installation of simple RC and pi (C- L-C) network filters in the input of the stereo equipment solved the problem

3. Schematic (1 of 2 Channels for Stereo) L2 Uses Amidon Core, Type FB-73-2401, A L =2500, 35 turns of magnet wire, approximate inductance calculated is 3 mH SPICE Model Created Using Ltspice IV

4. Formula for Calculating Inductance

5. Ferrite Cores Used Ferrite Core Characteristics and Source: http://www.amidoncorp.com/fb-73-2401/

6. Bode Plot of Pi Filter In/Out Response Output Amplitude Output Phase Input Amplitude and Phase (Green)

7. Subwoofer EMI Filter Much lower frequency response requirement for subwoofer allowed a single pole, RC filter to be used

8. Bode Plot of RC Filter In/Out Response Output Amplitude Output Phase Input Amplitude and Phase (Green)