Sinusoidal Tone Versus Modulation Operation

The main synthesizer has two modes: narrow and wide, corresponding to 10 kHz and 200 kHz loop bandwidths, respectively. During single tone (sine) generation, the narrow loop bandwidth is selected for the best possible phase noise performance. The specified phase noise is based on narrow loop bandwidth. Override the loop bandwidth defaults if your application requires it.

Ideally, narrow loop bandwidth should be used when modulation is turned on; however, the modulation implemented on the PXI/PXIe-5650/5651/5652 requires that the wide loop bandwidth is used, except for OOK modulation. Choosing wide loop bandwidth increases phase noise from 20 kHz and greater; the phase noise close to the carrier does not change. Loop bandwidths do not affect far out noise density; that is, the far out noise of the system remains unchanged.