Table of Contents | 
Down-conversion | Down-conversion: Code differences
Table of Contents | Down-conversion | Down-conversion: Code differences
The first down-conversion routine used the same half-band filter as used for the up-conversion. The resulting image suffered from severe ringing on the edges so a different filter was needed that would reduce this effect. The magnitude response of the filter used is shown in figure 4.
Figure 4 - Magnitude response of the down-conversion filter
This filter was developed using a similar technique to the up-conversion filter with a modified version of the 'brute-force' search C++ code. The filter has twelve taps and has been designed so the fourth and ninth taps are zero giving a number of 'active' filter taps equivalent to the up-conversion filter.