Name                                        Last modified       Size  Description

 Parent Directory                            09-Jul-2010 05:35      -  
 mdvh_AFC_FM_demo_WFM.grc                    17-Mar-2010 02:47    18k  
 mdvh_AFC_FM_demo_WFM.py                     17-Mar-2010 02:47     8k  
 mdvh_AFC_FM_demo_noaa_weather_satellite.grc 17-Mar-2010 02:47    18k  
 mdvh_AFC_FM_demo_noaa_weather_satellite.py  17-Mar-2010 02:47     8k  
 readme.txt                                  17-Mar-2010 02:48     1k  

Gnuradio AFC demo's

This directory contains gnuradio GRC and python example scripts for using AFC (Automatic Frequency Control) in an FM receiver.

There is not (yet) a AFC gnuradio block.
So these examples implement the AFC by lowpass filtering the FM demodulator output and putting the result in a variable sink.
The variable sink then sets the center frequency of the frequency translating channel filter.
This compensates any frequency offset or doppler drift.

To limit the performance penalty of calling python code from the samplestream, the code is only called once a second.

The critical settings of this feedback loop are:
AFC_gain        (float)
AFC_IIR_alpha   (float)
AFC_update_rate (float value: seconds between updates)

If you want to use this for a different FM signal type also make sure you set the right channel_bandwidth and max_dev (=Maximum FM frequency deviation in Hertz) 

Have fun

17 Mar 2010
Martin Dudok van Heel

Olifantasia