4. Begin designing the matched FIR filter.
Use the space bar to display both the filter response and the burst spectrum on the
same plot.
Use the Z key to shift the bursts main lobe up to the top horizontal line of the graph.
This makes it level with the filters peak lobe, which is always drawn tangent to the same
top line.
Figure 28 Example of a Poorly Matched Filter
5. Begin with the FIR length that was chosen previously in the Pb command, and use the
N and W keys to set an initial bandwidth equal to the reciprocal of the pulse width.
The main lobes of the two plots should more-or-less overlap. Experiment with changing
the FIR length and bandwidth to achieve a
filter with the following properties.
• The
filter width should be no greater than the burst spectral width. A wider
passband reduces the SNR of the received signal because out-of-band noise would
be allowed to pass.
• The DC gain should be as small as possible, preferably less than -65 dB.
• If there are conspicuous interference spikes at particular frequencies, try to adjust
the location of the
filter’s zeros so that the interference is maximally attenuated.
RVP900 User Guide M211322EN-J
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