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
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 LPF Model: File:Opamp-NE5532 lowpass-de-emp single.zip
Ltspice NE5532 dual op-amp library: File:NE5532.zip
High-Pass Filter (Pre-Emphasis)
LTspice HPF Model: File:Opamp-NE5532 highpass-pre-emp single.zip
LTspice NE5532 dual op-amp library: File:NE5532.zip