1. The length of wave meter and sampling rate of DDS signal source should be considered comprehensively when selecting carrier frequency. As we know, the phase step of DDS is directly related to the length of wave table and sampling rate. Once the carrier frequency is too large, the phase step of DDS will also be too large, which will inevitably lead to the decline of the number of waveform points of the carrier in each cycle. The smaller the waveform point is, the worse the spectrum purity of carrier signal will be.
2. When using arbitrary waveform generator to realize frequency scanning, the length of wave table of modulated wave should be considered. Because no matter how complex the sweep type you are editing, you are essentially editing the wave table of the modulated wave, so the larger the wave table of the modulated wave, the more complex your modulated wave can be edited, and the more complex the sweep mode can be realized. On the other hand, the larger the modulated wave table is, the higher the frequency variation accuracy of the output sweep signal will be.
3. The frequency of the modulated wave should not be too high.
This is similar to what is mentioned in point 1. When the frequency of the modulating wave is too high, the modulating wave itself is also a DDS signal source, so the waveform points of the modulating wave will be reduced. When the waveform points of the modulated wave are reduced, the details of the modulated wave will be missing, so the output sweep signal will be incomplete, and some key frequency points may be lost.
To sum up, when using arbitrary waveform generator to realize frequency scanning, only by comprehensively considering various restrictions, can better meet the needs of frequency scanning.