How to Design a Custom Digital Filter for the SBIII

How to Design a Custom Digital Filter
1. Select the Filter Detail Tab.

2. Select Proper Link, e.g., 851 Digital Filter for the SBIII 851-869 DL

3. Enter Filter Name, e.g., Filter 1

4. Enter Center Frequency. If multiple frequencies are passing through a particular filter, then this frequency will be the center of the band.
i.e., Ch1 855.9875MHz + Ch2 856.0125 MHz = Center Freq. 856 MHz

5. Select Filter Designer Tool

6. Highlight the Occupied Bandwidth number, and type in the desired bandwidth,
Note, all bandwidths must be entered in KHz. 

7. Highlight and enter the desired Adjacent Channel Offset, e.g. 100 KHz.  Typically, this number will be no greater that the closest Adjacent Channel.

8. Highlight and enter the desired Adjacent Channel rejection.  Default is set at 55 dB.  This can be increased as needed, e.g., 60 dB.

9. Passband ripple is set to a default of 0.5 dB.  This can be adjusted as needed.  Lowering the number will help to smooth out wider passbands.

10. Select Estimate, to allow the Filer Designer to calculate the filter and delay parameters.

11. Select Design. This will provide a graphical representation of the designed filter.  Once confirmed, select Save and Close.

12. Verify the filter settings on the Filter Tab.

13. Select Submit to program the filter.