Opamp-filters

Single-Supply (no negative voltage required) first-order (single-pole, 6dB/Octave, 20dB/Decade) audio filters.

These filters are optimised to provide 6dB/Octave for the 1200Hz and 2200Hz tones required for Packet or APRS transmissions over FM.

• Prototype #1

veroboard with HPF (left) and LPF (right)

circuit board inside enclosure

2014-11-02 -- completed a first prototype housing both the LPF and HPF and ready for testing with the TNC-Pi and IC-207H. A dual-opamp package is used (NE5532) and since both designs work off a single-supply all grounds can be nicely connected together. Further testing will reveal if this design is up for the task.

Low-Pass Filter (De-Emphasis)

LTspice trace and schematic of the filter in action

LTspice LPF Model: File:Opamp-NE5532 lowpass-de-emp single.zip

Ltspice NE5532 dual op-amp library: File:NE5532.zip

High-Pass Filter (Pre-Emphasis)

veroboard prototype of the High-Pass filter

LTspice trace and schematic of the filter in action

LTspice HPF Model: File:Opamp-NE5532 highpass-pre-emp single.zip

LTspice NE5532 dual op-amp library: File:NE5532.zip